bluuebunny/crossref_metadata_2025 huggingface dataset:
An Empirical Calibration of the StröMgren System for Late-Type Stars
Authors: Nelles B. , Richtler Th. , Seggewiss W.
Published: June 2019

The applicability of the Strömgren system for abundance determination of late-type stars has been shown by several authors (e.g. Eggen 1978b, Bond 1980, Ardeberg and Lindgren 1981). The aim of our contribution is not to present a completely new calibration. Rather we want to discuss the (b-y)-m1 diagram with an increased sample of spectroscopically analysed stars, hoping to eliminate some unsatisfying properties of previous approaches and to make improvements in terms of generality and reliability.
Spectroscopic Gravity Estimates for Late-Type Giants: Arcturus as an Example
Authors: Bell R. A. , Edvardsson B. , Gustafsson B.
Published: June 2019

The surface gravity of Arcturus is estimated from the strength of the MgH features (the Mg abundance being derived from MgI lines), from strong metal lines and from the FeI/FeII ionization equilibrium. The MgH lines give log g = 1.7 (cgs units) and 4375 K for the effective temperature. This value of log g is consistent with the gravity derived from the sample of strong pressure-broadened lines from FeI, CaI and NaI which gives log g = 1.6, and what we obtain from the ionization equilibrium of Fe, log g = 1.4. The corresponding estimates of the maximum error are 0.3, 0.2 and 0.5 dex, respectively. The mass of Arcturus is found to be in the interval 0.6–1.0 solar masses. It is concluded that the MgH features offer good possibilities for determining gravities of late-type stars, when good estimates of effective temperatures are available.
Infall of HVC's and the Origin of HI Supershells
Authors: Mirabel I.F.
Published: June 2019

Surveys for atomic hydrogen at very high velocities (|V| ≥ 140 km s–1) in the galactic center and anticenter regions of the sky reveal a net inflow of gas toward the Milky Way. In the anticenter, the collisions of infalling clouds with galactic material trigger the most energetic structural disturbance in the Galaxy, the “anticenter supershell”.
X-ray Haloes and Cooling Flows
Authors: Fabian A.C.
Published: June 2019

The properties of hot gaseous haloes in massive early-type galaxies are briefly reviewed. Gas flows in such haloes are complex yet so large-scale that they may guide us in the understanding of flows around disk galaxies. The intracluster medium is discussed as a further illustration of the properties of diffuse hot gas trapped in a gravtational well. Finally, the possibility of the existence of a significant diffuse medium in the Local Group, and in groups in general, is revived. Such a medium would generate a substantial disk-halo interaction with our Galaxy.
Opaque Spiral Disks: Some Empirical Facts and Consequences
Authors: Valentijn Edwin A.
Published: June 2019

A recent analysis of the surface brightness profiles of a complete sample of 9381 spiral galaxies extracted from ESO-LV (Lauberts and Valentijn, 1989) showed that many galaxy disks of especially Sb–Sc galaxies are opaque (Valentijn, 1990). This paper studied how the observed surface brightness μobs varies as a function of the observed axial ratio a/b, by fitting the data of samples of spirals with (1) assuming the a/b to give the inclination angle of the disks to the line of sight. A sample of galaxies that were fully transparent at the particular radius used for the test would have C ≃ 1, while C <~ 0.25 signifies opaque conditions, the transition value being heavily dependent on the spatial distribution of the absorbing material and the effect of multiple scatterings (Bruzual et al. 1988). The most frequently-used C values range from 0.5–0.9 (Holmberg 1975, de Vaucouleurs et al. 1976, Sandage and Tammann 1981). However, Valentijn (1990) derived C values well below 0.25 for large samples of spirals throughout the galaxy disks; this result is not significantly affected by selection effects in either magnitude, angular diameter or axial ratio, nor by the presence of bulges (at least for types Sb and later).
Boiling-Steaming Galactic Disk: Vertical Dust Jets in the Disk-Halo Interface
Authors: Sofue Y. , Wakamatsu K. , Malin D.F.
Published: June 2019

Optical photographs of highly-tilted, dust-rich nearby spiral galaxies like NGC253 have revealed numerous vertical dark filaments which we call vertical dust jets (VDJ). The VDJ exdend more than a few kpc from the disk in an almost coherent manner, while they are as thin as a few tens of pc. They are most likely due to boiling-steaming galactic disk, which ejects gas into the halo. The coherency suggests that VDJ trace large-scale poloidal magnetic lines of force.
The Galactic Gravitational Potential
Authors: Creze M.
Published: June 2019

Observational constraints on the galactic potential and modelling aspects are reviewed. The following conclusions come out. The mass distribution generating the galactic gravitational potential should include a bulge to account for the innermost features of the rotation curve, an extensive massive corona responsible for a flat rotation at large radius, and a disc able to produce a rotation curve as given by Rohlfs and Kreitschmann (1988) and a vertical force law Kz as from Bienaymé et al. (1987). We still know very little about the potential more than 1500 pc above the galactic plane.
Hydrostatic Equilibrium of Gas-Field System in the Galaxy and its Stability
Authors: Stephens S.A.
Published: June 2019

The stability of the gas-field system in the Galaxy is examined to show that it is difficult to maintain a stable configuration due to numerous energy releasing phenomenon occurring in the Galaxy. However, it is argued that, as in the case of our atmosphere, hydrostatic equilibrium is expected in the Galaxy on a global scale. A summary of the advances made in the study of the global equilibrium is presented. The major postulates and predictions from some of these studies are compared with the observations. The usefulness of detailed observation of nearby edge-on galaxies in radio and X-ray regime is brought out.
Static versus Dynamical Cosmic-ray Halos
Authors: Jones Frank C.
Published: June 2019

The dynamical halo of the Galaxy offers a natural explanation for the form of the variation of cosmic-ray path length with energy. The variation above 1 GeV per nucleon can be understood as due to the variation of the diffusion coefficient, and hence the resident time in the galaxy, with energy. The flattening of the curve below 1 GeV per nucleon is seen to mark a transition to a convection dominated regime where the variation of the diffusion coefficient is no longer a determining factor. It is possible that the random motion of the cosmic rays about the galaxy that prevents us from seeing their sources in a clear manner may enable us to extract information about the galaxy at large and learn something about its large scale motions.
A Few Points on the Stability of the Solar System
Authors: Laskar J.
Published: June 2019

The secular equations which were used to exhibit the chaotic behaviour of the solar system (Laskar, 1989) are established here in a Hamiltonian framework. The integration of the former secular equations over 400 Myr showed that the two resonant arguments and given in (Laskar, 1990) present both transitions from libration to circulation. During the circulation of the first argument, temporary libration of the argument is observed, revealing resonance overlap beetween these two resonances, which explains the existence of a large chaotic zone for the motion of the solar system.
Numerical Experiments on the Motion of the Outer Planets
Authors: Quinlan Gerald D.
Published: June 2019

We have integrated the motion of the four Jovian planets on Myr timescales in fictitious solar systems in which the orbits differ from those of the real solar system. A change of ≲1% in the major axis of any one of the planets from its real value can lead to chaotic motion with a Lyapunov exponent larger than 10-5 yr−1. A survey of fifty solar systems with initial conditions chosen at random from a reasonable probability distribution shows the majority of them to be chaotic.
Puzzles and Prospects in Planetary Ring Dynamics
Authors: Goldreich Peter
Published: June 2019

I outline some of the main processes that shape planetary rings. Then I focus on two outstanding issues, the role of self-gravity in the precession of narrow rings and the dynamics of Neptune's arcs. By airing these well-defined but unsolved problems, I hope to encourage others to join me in the quest for their solutions.
New Results on the Motions of Asteroids in Resonances
Authors: Dvorak R.
Published: June 2019

In this article we present a numerical study of the motion of asteroids in the 2:1 and 3:1 resonance with Jupiter. We integrated the equations of motion of the elliptic restricted 3-body problem for a great number of initial conditions within this 2 resonances for a time interval of 104periods and for special cases even longer (which corresponds in the the Sun-Jupiter system to time intervals up to 106years). We present our results in the form of 3-dimensional diagrams (initialaversus initiale, and in thez-axes the highest value of the eccentricity during the whole integration time). In the 3:1 resonance an eccentricity higher than 0.3 can lead to a close approach to Mars and hence to an escape from the resonance. Asteroids in the 2:1 resonance with Jupiter with eccentricities higher than 0.5 suffer from possible close approaches to Jupiter itself and then again this leads in general to an escape from the resonance. In both resonances we found possible regions of escape (chaotic regions), but only for initial eccentricitiese> 0.15. The comparison with recent results show quite a good agreement for the structure of the 3:1 resonance. For motions in the 2:1 resonance our numeric results are in contradiction to others: high eccentric orbits are also found which may lead to escapes and consequently to a depletion of this resonant regions.
Resonance p:p+q in Satellite Orbits
Authors: Grosso Pedro R. , Sessin Wagner
Published: June 2019

In this paper we consider the motion of a satellite whose mean motion is commensurable with the frequency of the rotational motion of the planet in the ratio p:p+q.
Rotational Behavior of Cometary-type Bodies
Authors: Bois Eric , Oberti Pascal , Froeschlé Claude
Published: June 2019

The present paper deals with a general dynamical qualitative study of the rotational motion for cometary-type bodies submitted to gravitational torques. Numerical experiments of the evolution of comet nucleus attitude have been then performed, including the Sun and Jupiter's disturbing torques in the model. Results show small effects of the solar gravitational perturbation for Halley-type orbits. Only a very close-approach with Jupiter induces notable effects. The latter configuration presents some interesting sensitivity to initial conditions.
Planetary Nebulae: An Introductory Review
Authors: Aller Lawrence H.
Published: June 2019

Planetary nebulae constitute a popular field of investigation because they offer a unique opportunity to study the final stages of stellar evolution before a star dies. They supply challenges not only to the stellar evolution expert but also to the spectroscopist, to the student of galactic structure, and to all observers, whether one works in the optical, ultraviolet (UV), infrared (IR) or radio-frequency (r.f.) ranges. They offer insights into properties of dusty, low-density plasmas which may help unravel problems of the interstellar medium (ISM) and quasars. Finally, many are aesthetically beautiful art creations.
New and Misclassified Planetary Nebulae
Authors: Kohoutek L.
Published: June 2019

Since 1978 85 new objects have been classified as planetary nebulae. They are listed in Table 1 which gives the designations, names, coordinates and the references to the discovery. In the list of misclassified planetary nebulae (Table 2) 33 objects have been included. Principal criteria have been summarized which can help to distinguish planetaries from other objects. They refer to observable properties and are valid only in a statistical sense.
Recent Work on Bipolar Nebulae
Authors: Cohen Martin
Published: June 2019

Recent results obtained from studies of bipolar nebulae with a variety of techniques are described. Nebular polarization maps and spectropolarimetry, near-infrared spectroscopy, far-infrared photometry, radio maser and continuum work all have contributed to our knowledge of this heterogeneous class of objects. Some are certainly pre-main-sequence; others are likely to represent the rapid transition from red giant to planetary nebula. At least one dust-shrouded carbon star (CIT 6) and one visual binary with an O-star primary (MWC 349) have bipolar structure. Equatorial dusty disks must be common occurrences at different phases of stellar evolution.
Radio Observations of Planetary Nebulae
Authors: Scott P. F.
Published: June 2019

A discussion of radio observations for the period up to 1979 forms part of the general review given at the 1979 IAU General Assembly by Terzian (1980) and I shall be concerned here mainly with later results. With the advent of improved radio telescopes and techniques, in particular the coming into full operation of the Very Large Array (VLA), there has been an increasing interest in compact and proto-planetary nebulae and I shall discuss these observations in a separate section of this review.
Sulphur Abundances in Three Halo Planetary Nebulae
Authors: Barker T.
Published: June 2019

The intensities of the (S II) 6717, 31 Å and (S III) 9532 Å lines have been measured for the first time in the three known extreme halo planetaries. Preliminary estimates of the S/H ratios are: (4.7 ± 6.5) x 10−7 for 108 – 76o1, (1.4 ± 0.6) x 10−7 for K 648, and (2.0 ± 1.3) x 10−7 for 49 + 88o1. The S/H ratio in K 648 (the planetary in M 15) is 0.014 of that measured in the Ring Nebula (Barker, 1980, Ap. J., 240, 99), consistent with the Fe/H abundance of about 1/100 solar found (Cohen, 1978, Ap. J. 223, 487) in the stars in M 15. The average of the S/O ratios in the halo planetaries is an eighth the value in the Ring Nebula, similar to the low Ar/O ratios found previously (Barker, 1980, Ap. J. 237, 482). The implication is either that the abundances of lighter elements such as O have been enhanced by nuclear reactions in the planetary progenitors or that S and Ar were synthesized galactically at a slower rate than lighter elements. In either case, it appears that S and Ar may be more representative of the true heavy metal abundances in planetaries than O.
Deduction of Planetary Nebulae Properties from Long Period Variable Precursors
Authors: Bessell M. S. , Wood P. R.
Published: June 2019

Infra-red (JHK) photometry of long period variables (LPV) in the Magellanic Clouds has shown that the LPV's can be divided into core helium burning supergiants and asymptotic giant branch (AGB) stars. Application of the pulsation theory allows masses to be derived for the LPV's while stellar evolution theory allows core masses to be derived for the AGB stars. By considering evolution of the LPV's in the (Mbol,P) diagram, estimates of planetary nebula mass and planetary nebula nucleus mass are derived as a function of initial mass. Spectra of the LPV's suggest that many low mass planetary nebulae in the Magellanic Clouds should be carbon rich while the more massive nebulae may be nitrogen enhanced.
Comparison of Planetary Nebulae and Symbiotic Star Emitting Regions
Authors: Keyes C. D.
Published: June 2019

The spectra of symbiotic stars generally display many emission lines seen in moderate to high-excitation planetary nebulae, but are superposed upon a strong continuum characteristic of a cool star, typically of type M. Furthermore, the spatial distribution of symbiotics has been noted to resemble that of planetaries. These similarities suggest that the symbiotic stars and planetary nebulae might have some relationship (causal or otherwise) or that they might arise from similar progenitors.
Planetary Nebulae and Seyfert Galaxies - Similarities and Differences
Authors: Osterbrock Donald E.
Published: June 2019

Knowledge gained in the study of planetary nebulae has been, and can be further, transferred to understanding active galactic nuclei. Photoionization is the main energy-input mechanism in the narrow-line regions, and probably although by no means certainly in the broad-line regions as well. There are many detailed differences because of the much “harder” input spectrum in active galactic nuclei, compared with planetary nebulae. A tentative model of the structure of the gas distribution in a Seyfert-galaxy nucleus is presented.
The Kinematical Structure of the Bipolar Nebulae M2-9 and M1-91
Authors: Carsenty U. , Solf J.
Published: June 2019

Both nebulae are of similar appearance consisting of a central core and two highly symmetrical, elongated lobes. Using the large vertical Coude spectrograph of the 2.2-m telescope on Calar Alto, Spain, we obtained long-slit spectra in the red of high spectral (12 km s−1 FWHM) and spatial (2″) resolution from various positions within the nebulae. Our data indicate high similarity in the kinematical structure of both nebulae. The central cores are dominated by very broad emission lines. The Hα profiles (width ≈ 1600 km s−1 at 5% level in M2-9) exhibit an absorption feature blue-shifted by ≈ 20 km s−1 relative to the emission maximum, similar to profiles observed in some Herbig-Be-stars.
Low Temperature Dielectronic Recombination Coefficients for Ions of C, N and O
Authors: Nussbaumer H. , Storey P.J.
Published: June 2019

Dielectronic recombination coefficients have been calculated for some ions of C, N and O by Storey (1981, Mon. Not. R. astr. Soc., 195, 27P). Using the same approach, we have extended those calculations to all other ions of C, N and O for which a dielectronic contribution to the total recombination coefficient might be expected at nebular temperatures. Recombination coefficients have been calculated in the temperature range from 5000 K up to the temperature at which the Burgess general formula becomes valid. The total dielectronic recombination coefficients are fitted to a simple function of the electron temperature.
Detection of T-Tauri Star Candidates in the Canis Major Star-Forming Region and its Implications
Authors: Wiramihardja Suhardja D. , Kogure Tomokazu , Nakano Makoto , Yoshida Shigeomi
Published: June 2019

We have made a survey of Hα-emission stars in the CMa R1 region with the 105cm Schmidt telescope at the Kiso Observatory. In an area of about 37 square degrees, a total of 107 Hα-emission stars (V = 6-15 mag.) was found, and, for all of them, the photographic photometry in the UBV system has been carried out.
A Survey of the M17SW Giant Molecular Cloud for H-alpha Emission Stars
Authors: Shinohara Masao , Ogura Katsuo
Published: June 2019

The M17SW giant molecular cloud extends over 4° (∼ 160 pc) at the south-west of the giant H II region M17. The distance and the mass of the cloud are estimated to be approximately 2.2 kpc and 3x105 M⊙, respectively.
Infrared CO Emission from WL 16
Authors: Thompson Rodger I.
Published: June 2019

The Rho Ophiuchi source WL 16 is the second Young Stellar Object (YSO) found to have infrared CO emission bands. IRAS observations show that WL 16 is far less luminous (∼ 14 L⊙) than the first source of infrared CO emission, BN (> 5000 L⊙). Also in contrast to BN, the CO emission from WL 16 represents a significant fraction of the total luminosity. The 2.3 μm first overtone CO emission bands were observed with the Steward Observatory Fourier Transform Spectrometer at the 2.3 m telescope.
The Orion Nebula and the Sun as Probes of Galactic Chemical Evolution
Authors: Peimbert M.
Published: June 2019

The solar and the Orion nebula chemical abundances are discussed; their chemical compositions differ at least in the O/H, He/O and 12C/13C ratios. A review of processes that could be responsible for these differences is presented.
Induced Star Formation in M17: High Resolution NH3 and IR Observations
Authors: Felli M. , Massi M. , Stanga R. , Churchwell E.
Published: June 2019

A VLA radio continuum study of the H II region M17 (Felli, Churchwell and Massi, 1984) has shown the presence of an elongated sharp arc structure in the South Bar of the nebula, in a region of heavy obscuration. The arc has been interpreted as an ionization boundary, viewed edge on, located between the diffuse H II region, to the east, and a dense component of the extended molecular cloud, to the west. About 3″ to the west of this arc, an ultra-compact H II region has been found. This has a shell type structure, a linear diameter of 0.004 pc and probably is the result of induced star formation in the molecular cloud produced by the pressure front preceding the ionization front.
Images of Star Forming Regions in CO and H2
Authors: Gatley Ian
Published: June 2019

A collaboration between Nobeyama Radio Observatory and UKIRT has produced high resolution images in CO and H2 of the star forming regions DR21, Orion, and M17. In each case the images in the two species are remarkably similar. This is a striking result, for the H2 traces a very hot component of the interstellar medium, either shocked to temperatures around 2000 K or highly excited by ultraviolet fluorescence.
CO J = 3-2 and 4-3 Observations of Molecular Clouds
Authors: White Glenn J. , Rainey Ruth , Avery Lorne , Phillips Peter , Griffin Matthew , Monteiro Tania , Richardson Kevin , Cronin Nigel , Harten Ron
Published: June 2019

We report on extensive submillimetre wavelength observations in the CO J = 3-2 and 4-3 lines towards a sample of star formation regions. The observations have been obtained using the Queen Mary College Submillimetre Heterodyne Receiver at the UKIRT 3.8 m telescope. The data include observations and maps of NGC 2024, S88, W3, S140, CRL2591, NGC 2264, K3-50, G35.2-0.74, ρ Oph A, M17, W51, S68, S106, NGC 1333, DR21 and W49. Several new bipolar flow sources have been detected in NGC 2024, S88 and NGC 2264. Comparisons between the spectra in the CO J = 1-0, 2-1, 3-2 and 4-3 transitions will be discussed in terms of their excitation, in particular for the gas in the high velocity line wings, where we have attempted to estimate the densities and relative abundances of the flow material.
Relationship of OH and H2O Masers
Authors: Forster J. R. , Caswell J. L.
Published: June 2019

Detailed maps of 70 OH and H2O masers associated with star-forming regions have been made with the VLA at an angular resolution of ∼2″ arc. The absolute position accuracy is 0″.5 for both the OH and H2O observations, and the relative position accuracy of maser spots within a group is 0″.1 for each species. For about half of the sources compact H II regions are detected at 22 GHz with 0″.1 positional accuracy relative to the strongest H2O maser. Preliminary results are presented, with emphasis on the spatial relationship between the OH and H2O masers and compact H II regions.
VLA Search for Optically Thick H II Regions in Luminous Embedded Infrared Sources
Authors: Ho Paul T.P. , Rengarajan T. N.
Published: June 2019

We have searched for radio continuum emission at 15 GHz from a number of deeply embedded protostar like infrared objects, using the B configuration of the VLA. The aim was to get high resolution (1″) and high sensitivity maps. For 10 objects (NGC 7538-IRS 3, GL 989, GL 4029-IRS 1, GL 437N, GL 2789, NGC 1333-IRS 13, S235B, GL 4029-IRS 2, R Mon and OMC2-IRS 3) we did not detect radio emission, the 3 upper limit being 0.3 – 0.5 mJy. Positive detections were made for W33A, 0MC2-IRS 4, S 235-IRS 1 and NGC 6334V-IRS 4. The cleaned maps for these objects are shown in Figures 1-4.
S201: The Ionized Skin of a Molecular Blob
Authors: Felli M. , Cesaroni R. , Hjellming R. M.
Published: June 2019

S201 is an optically visible H II region whose ionizing star is hidden to the sight by heavy obscuration. The radio continuum surface brightness distribution observed at 6-cm with the VLA can be described by two distinct components: a) an extended diffuse structure, which closely reproduces the shape of the observable nebulosity, and b) a sharp bright arc feature on the east side of the extended component, unresolved towards the outside at the resolution of ∼ 4″.
Hollow Cylindrical Lobes with a Helical Velocity Field of the L1551 Bipolar Flow
Authors: Uchida Yutaka , Kaifu Norio , Shibata Kazunari , Hayashi Saeko S. , Hasegawa Tetsuo
Published: June 2019

Observations of the structure and the velocity field in the L1551 bipolar flow were made with the 45m telescope at Nobeyama in the 115GHz 12CO J = 1 – 0 line with high spatial resolution. It was found that the bipolar flow lobes have a clear hollow cylindrical structure and show evidence of a helical velocity field. They appear to rotate in the same direction as the CS disk found by Kaifu et al. (1984). The velocity of the flow in the bipolar directions increases with distance up to ∼ 3′ from the central object, IRS 5. These characteristics coincide with those predicted by the magnetodynamic theory proposed by Uchida and Shibata and indicate the essential importance of the magnetic field in producing such flows and also in the star-formation process itself through the enhancement of angular-momentum loss.
Polarization Observations in the Near Infrared as a Probe of Bipolar Flow Regions
Authors: McLean Ian S.
Published: June 2019

It is shown that near infrared polarization is to be expected in star-forming regions and new observations with the UK Infrared Telescope (UKIRT) are reported which include the discovery of a molecular hydrogen reflection nebula in Orion and an extensive dust cloud around S106.
IR Line and Continuum Emission from Bipolar Outflow Sources
Authors: Smith Howard A. , Fischer J. , Mozurkewich D. , Schwartz P. R. , Geballe T. R.
Published: June 2019

Most of our understanding of BPF's is based on observations of the neutral and ionized gas in bright, high luminosity sources. Data on low luminosity (L ≲ 30 L⊙) objects has now become more available (e.g. Frerking and Langer, Astrophys. J. 256, 523, 1982) permitting a test of models at this end of the luminosity range. We have performed a series of multi-wavelength observations, emphasizing low luminosity objects.
Molecular-Line Studies of the Bipolar Flow Source GL490∗
Authors: Kawabe R. , Kaifu N. , Hayashi S. S. , Hasegawa T.
Published: June 2019

We have made HCO+ (J = 1-0), HCN (J = 1-0) and CS (J = 2-1) observations of a bipolar flow source GL490 (Lada and Harvey 1981; Snell et al. 1984) using the Nobeyama 45-m telescope with 20″ resolution. A HCO+ spectrum obtained toward a central infrared source (Harvey et al. 1979) has prominent line wings extending up to 15-25 km s−1 from the line center (Figure 1). Figure 2 shows a map of HCO+ high velocity emission more than 8 km s−1 off the line center. The emission has “head-tail”-structures in both the blue- and the red-shifted sides; a “head” with stronger emission and a “tail” with weaker narrow ridge emission extending to the opposite side of the “head” through the center. The “head” emission has the same bipolar structure as the CO flow. Intermediate velocity emission at 38 km s−1 from the line center shows (1) a narrow ridge elongated in the NE-SW direction, at the blue-shifted side, and (2) a pair of shell-like structures symmetrically placed SW and NE of the center of the high velocity emission, at the red-shifted side (Figure 3).
CS(J = 2-1) Observations of B335
Authors: Kameya Osamu , Hasegawa Tatsuhiko , Hirano Naomi , Takakubo Keiya , Seki Munezo
Published: June 2019

CS(J = 2-1) observations of B335 are carried out using the NRO 45-m telescope with a 16″ beam. We get many self-reversed profiles with good S/N ratio. Assuming that this region consists of a core and a halo, we get the molecular hydrogen density and the CS relative abundance in the halo. The CS wings are located within the cavity of the CO wing (Goldsmith et al. 1984).
The Circumstellar Environment of LkHα 234
Authors: Wilking B. A. , Mundy L. G. , Schwartz R. D.
Published: June 2019

We present high resolution (HPBW = 5 arcsec) continuum and molecular-line observations of the circumstellar environment of the emission-line star LkHα 234 made with the Owens Valley Millimeter-Wave Interferometer. These 98 GHz observations have revealed an unresolved continuum source coincident with the star and a 10 000 by 17000 A.U. ridge of enhanced CS(2-1) emission which peaks ∼ 4″ east of the star. The resulting spectral dependence for the radio continuum emission of ν1.5 is most easily interpreted as arising from a partially ionized stellar wind. Attempts are made to describe the properties of the CS emission in terms of a rotating molecular disk which would link LkHα 234 with large scale mass loss activity in the cloud. However, it appears most likely that the CS emission is arising from a dense (n(H2) ∼ 106 cm −3) condensation of gas adjacent to, but not dynamically associated with, the star.
Infrared Structure of OMCI
Authors: Nakada Yoshikazu
Published: June 2019

Although infrared observations are ideal to study a molecular cloud, an infrared spectrum alone is not enough to determine the physical parameters in the source (Rowan-Robinson 1980). An intensity gradient in sub-millimeter wavelengths was considered by some authors as a measure of the density fall off. But the derived distribution laws are still controversial (Scoville and Kwan 1976, Westbrook et al. 1976, Keene et al. 1982). Other parameters entering the interpretation of the infrared observations are the emissivity and the temperature distribution of the dust. In most models of molecular clouds, major efforts have been devoted to accurately determine the dust temperature for the assumed density gradient and emissivity (Jones and Merrill 1976, Leung 1976, Unno and Kondo 1977, Rowan-Robinson 1980).
Are Bipolar Jets Precessing?
Authors: Fukue Jun , Yokoo Takeo
Published: June 2019

No one has drawn attention as to whether bipolar jets precess or not. We examine here the possibility of precession of bipolar jets from a theoretical point of view (Fukue and Yokoo 1986).

We first characterize various models proposed for bipolar jets in the light of precession. That is, can they admit precession? If they can, how long is a precessional period P?
Magnetic Field Amplification and Polar Jet Formation in Protostars
Authors: Hinata S.
Published: June 2019

There is a simple relationship among moment of inertia I, rotational kinetic energy K, and momentum L given by (David Layzer, private communication), 2IK ≧ L. During the Hayashi phase a rotating protostar will amplify the trapped magnetic field by a dynamo-like process. Since the rotation is expected to be fast, many unstable modes will be excited and will grow exponentially in time until some nonlinear processes saturate the amplitude. However, it may happen that the reduction in rotational kinetic energy becomes so large that without increasing the moment of inertia the inequality given above may not be satisfied. The only way to increase the moment of inertia is to move the mass outward. This can be done by transferring the angular momentum outward through the magnetic field. So we will have a fast rotating mass shell at the outer edge of the star. Further transfer of angular momentum will push the shell against the accretion disk; the moving masses of the disk will divert the mass flow along the background magnetic field which extends perpendicular to the accretion disk. This results in the hollow cone jets from both poles because the outward motion is primarily on the equatorial plane.
The Effect of the Gravity of a Circumstellar Torus on Bipolar Jets
Authors: Fukue Jun
Published: June 2019

We examine the hydrodynamical wind-type jet in the funnel formed along a rotational axis of accretion tori surrounding a proto star, taking into account the gravitational field produced by torus-gas (Fukue and Yamamoto, in press, 1986). In the current models (e.g. Fukue 1982, 1983), an astrophysical jet was assumed to be accelerated along the funnel considering only the gravitational field of the central object.
A Single Fragmentation Law? Theoretical and Observational Evidence
Authors: Di Fazio A. , Capuzzo Dolcetta R.
Published: June 2019

In the light of the growing interest for the modes of formation of various astronomical objects, a relevant amount of data were collected and treated to obtain mass spectra. Statistical comparisons of the data suggest that a single process drives the formation of the various self-gravitating objects.
New Results on the Coagulation Equation
Authors: Bastien Pierre , Lejeune Claude
Published: June 2019

In attempting to reproduce the initial stellar mass function, we solved analytically the coagulation equation with an explicit time dependence in the coagulation rate in order to simulate the gravitational collapse of the fragments upon themselves as they move within the progenitor cloud. Two separate cases have been studied, with and without a mass dependence in the coagulation rate. The solution show that (1) inclusion of self-gravitation is very important and can change the results to the point of preventing coalescence to work altogether, depending on the values of the two free parameters, (2) the precise form of the mass dependence of the coagulation rate is not of prime importance in most situations of astrophysical interest, and (3) coagulation alone is not sufficient to yield a realistic mass spectrum and fragmentation must also be taken into account. Coagulation is more efficient for massive fragments and fragmentation for the smaller ones. These results are applied to different regions: star clusters, associations, and starburst regions.
Sequential Star Formation inside the Young Stellar Associations of the Magellanic Clouds
Authors: Lortet M. C. , Testor G. , Niemela V. , Heydari-Malayeri M.
Published: June 2019

While much work has been devoted to the history of star formation in the Magellanic Clouds at large spatial and time scales, little has been done on the details of sequential formation at the scale of a few 106 or 107 years and of less than 1000 pc.
Bursts of Star Formation in Galaxies
Authors: Wynn-Williams C. G.
Published: June 2019

A minority of spiral galaxies is currently undergoing bursts of intense star formation. This paper reviews studies that have been made of these galaxies at visible, radio, and infrared wavelengths, with an emphasis on results that have emerged since the IRAS survey.
Hyperactive Star Bursts in Clumpy Irregular Galaxies
Authors: Heidmann J.
Published: June 2019

Clumpy irregular galaxies have been identified as giant irregulars with a clumpy structure. Investigations in the visible, UV, radio centimetric, X-ray and far infrared demonstrated that the clumps are hyperactive bursts of star formation, each equivalent to a hundred giant HII regions like 30 Doradus or NGC 604. In spite of their strong activity, their linear size is smaller than half a kpc, leading to an “olive jar” model with very peculiar physical conditions. These could be related to the non-detection of the 2.6-mm CO line and to our discovery in a clump of the first known case of a strong, compact, variable radio source which is not a galactic nucleus.
Star Formation in the Spiral Galaxy M33
Authors: Viallefond F.
Published: June 2019

The spiral galaxy M33 has been observed at several frequencies from the ultraviolet to the radio regions. The observations at 2030 A have been presented by Milliard (1984); the radio data obtained with the WSRT and the VLA are presented and analyzed in a series of papers (Viallefond and Goss 1986, and references therein).
Anemic Galaxies: Evidence for a Threshold in Star Formation Processes
Authors: Guiderdoni B.
Published: June 2019

From a sample of Virgo Cluster and “field” disk galaxies, it is shown that a critical value of the HI surface density discriminates between RDDO anemic and “healthy” spirals. Below this threshold, at least massive stars do not form any more and the galaxy gets the anemic appearance. The influence of the HI content on the global star formation rate is discussed in the context of present models (Elmegreen 1979, Seiden and Gerola 1979, Dopita 1985), as well as the fate of disks in cluster and “field” environments. The existence of this threshold is an issue for the problem caused by the short gas consumption time scales derived from the observations of spiral galaxies.
Star Clusters in Local Group Galaxies
Authors: Olszewski Edward W.
Published: June 2019

In this paper I will try to give the flavor of two different concepts of stellar population, namely, the population of cluster systems within galaxies, and the stellar populations within individual clusters. I hope to show, in concert with other papers in this volume, that a generic vision of Population I and II has been outdated for a long time. I believe that it is still proper to talk about populations within individual objects; in the case of galaxies, one might make a correspondence of populations with the important star forming events in the history of a galaxy.
Stellar Populations at Large Redshifts
Authors: O'Connell Robert W.
Published: June 2019

It is now possible to probe stellar populations at large lookback times. The Butcher-Oemler Effect in distant clusters is unambiguous evidence for unexpectedly recent evolution of disk galaxies in dense environments, probably through starbursts induced by interactions. Recent applications of the “red envelope” test at z ≲ 1 indicate that some luminous galaxies formed ~ 10-13 Gyr ago.
New Mg2 Indices from New Model Atmospheres
Authors: Chavez M. , Malagnini M.L. , Morossi C.
Published: June 2019

A new set of spectral indices computed for the Mg feature at 5175 Å is presented. The spectral indices were computed using the most recent grid of model atmospheres and programs to produce synthetic spectra (Kurucz 1993; CD-Rom 18) for the temperature range 4000-6000 K, and gravity interval log g = 1.5-4.5. The indices reported here refer to solar chemical abundance.
Complete Stellar Models: Interior and Spectral Evolution of Massive Stars
Authors: Schaerer D. , De Koter A. , Schmutz W.
Published: June 2019

We present the first models of massive stars, where the interior structure is coupled to a spherically extended, metal line blanketed non–LTE atmosphere with a wind. This is accomplished with the Geneva stellar evolution code and the non–LTE atmosphere code of de Koter et al. (1993). The method described in Schaerer & Schmutz (1994) is used to treat line blanketing. A first account of this work is published in Schaerer et al. (1994).
Automating the Classification of Stellar Spectra
Authors: Jones Coryn A.L. , Von Hippel T.
Published: June 2019

We are automating the multi-parameter classification of stellar spectra within the MK system. The increased rate at which spectra are gathered by increasingly larger telescopes, fibre systems and efficient CCD detectors necessitates the need for automation of stellar classification. As well as greatly speeding up this process, an automated scheme would give reproducible results, would arguably be more objective, and would give quick and useful reporting of classification uncertainties.
A Project for Investigation of the Stellar Populations of the Galactic Disk
Authors: Straižys V. , Philip A. G. D.
Published: June 2019

All models of the visual Galaxy are verified only in fields with galactic latitude |b| > 20°. At lower galactic latitudes, all the broad-band photometric systems and the majority of medium-band photometric systems fail to classify stars due to interstellar reddening. For the Vilnius photometric system the interstellar reddening is not an obstacle.
Investigation of Suspected Red Horizontal Branch Stars in the Galactic Field
Authors: Tautvaišienė G.
Published: June 2019

The chemical composition of 11 suspected RHB stars in the galactic field was recently analyzed using high-resolution spectra obtained with the 6-meter telescope of the Special Astrophysical Observatory, North Caucasus. We summarize here some of the main conclusions obtained from comparison of the abundances of the RHB stars with available abundances of giants and dwarfs (hereafter G and D).
Evidence for Primordial Abundance Variations in the Globular Cluster 47 Tuc
Authors: Croke B.F.W. , Stathakis R.A. , Cannon R.D. , Hesser J.E. , Bell R.A.
Published: June 2019

The FOCAP multi-object system on the Anglo-Australian Telescope (AAT) has been used to observe 35 faint stars (V > 18, Mv > + 4.6) and 83 stars with V < 18 in 47 Tuc. The large sample of stars well below the turnoff permits us to examine abundance variations in relatively unevolved stars for the first time. Our spectral resolution (2.7Å) is greater than that used in previous studies.
Three New Contact Binaries Near the Centre of NGC 6121 (M4)
Authors: Menzies J. W.
Published: June 2019

The central 2×3 arcmin2 region of M4 has been observed as part of a programme to find blue stragglers in globular clusters. A preliminary analysis has been carried out of 58 V frames and 65 I frames obtained on two separate occasions with an RCA CCD on the 1.0m telescope at Sutherland.
Evolutionary Aspects of the CMD of NGC 6553
Authors: Catelan M. , Barbuy B. , De Freitas Pacheco J. A. , Ortolani S. , Bica E.
Published: June 2019

We have investigated the V, B – V “clump” morphology of the globular cluster NGC 6553 (Ortolani et al. 1990, OBB90) through synthetic horizontal branch (SHB) models. Catelan's (1993) computations were extended to more metal-rich compositions, following Sweigart (1987) and Castellani et al. (1991), and transposed to the observational plane on the basis of VandenBerg's (1992) colour transformations and bolometric corrections. Observational scatter has also been added. In general, the SHB models are very clumpy, unlike the observed feature, which seems extended and peculiarly tilted. However, for particular combinations of helium abundance, metallicity, and mean mass on the HB, tilted models result, being however significantly less sloped and wider than observed. The NGC 6553 field is differentially reddened by ΔE(B – V) ≈ 0.06 (OBB90), which has been modelled, but which implies a CMD scatter which is smaller than the one originating from evolution away from the zero-age HB alone. We have also investigated the age of the cluster (ΔV method) and location of the red giant branch “bump,” in comparison with 47 Tuc. Since the helium and α-elements abundances are not known for NGC 6553, three chemical evolution scenarios have been considered, following the method of de Freitas Pacheco (1993). Details can be found elsewhere (Catelan et al. 1994).
Stellar Populations in the Pegasus Dwarf Galaxy
Authors: Lee Myung Gyoon
Published: June 2019

The Pegasus dwarf galaxy (DDO 216) is a resolved irregular galaxy. We present a study of stars in this galaxy based on BV RI CCD photometry obtained using the Palomar 1.5m telescope. The color-magnitude diagrams show (a) a dominant red giant branch (RGB) population, (b) a small number of asymptotic giant branch (AGB) population above the tip of the RGB (TRGB), and (c) a sparse popultion of massive young stars including the brightest red supergiants. The mean metallicity of the RGB has been estimated from the color of the RGB at MI = −3.5 mag: [Fe/H] = −1.5 ± 0.2 dex. The distance to this galaxy has been measured using the I-magnitude of the TRGB: (m – M)0 = 25.13 ± 0.11 mag (d = 1060 ± 50 kpc) (see Lee et al. 1993). This value is significantly smaller than the Cepheid distance estimate by Hoessel et al. (1990), (m – M)0 = 26.22±0.20 (d = 1750±160 kpc).
A Decoupled Nucleus in NGC 1052
Authors: Sil'chenko O.K.
Published: June 2019

The central part of NGC 1052 has been observed at the prime focus of the 6m telescope with the Multi-Pupil Spectrophotometer equipped with a two-dimensional IPCS. Ninety-nine spectra over the central 14.5″x11″ are registered in the spectral range of λλ4700 – 5400 AA and are used to map ionized-gas velocities (by [OIII]λ5007) and to derive radial profiles of absorption-line equivalent width for MgIλA5175, FeIλ5270, and Hβ.
Study of the Stellar Populations in NGC 3516
Authors: Serote-Roos M. , Boisson C. , Joly M.
Published: June 2019

Our aim is to quantify the stellar population within the nuclear regions of AGN by means of long slit spectroscopic observations in the optical range (5000-10000Å), including MgI, NaI, TiO, CN, CaIIT. We wish to determine whether there is a relationship between central activity and stellar population, and to determine the nature of the featureless continuum.
The UV Content of Virgo Cluster Galaxies
Authors: Brosch Noah
Published: June 2019

I present a preliminary analysis of three UV images of the Virgo cluster region, obtained by the FAUST experiment (Bowyer et al. 1993) in April 1992. FAUST is a wide-field imaging telescope covering an 8° area with effective resolution of 3′.5. The experiment was constructed by the Berkeley Space Astronomy Group together with the Laboratoire d'Astrophysique Spatiale of the CNES. It operated on board the Shuttle during the mission ATLAS-1.
Line-Strength Profiles in Early-Type Galaxies
Authors: Fisher David , Illingworth Garth , Franx Marijn
Published: June 2019

Line-strengths and their gradients in Mg, Fe, and Hβ have been determined for a sample of 9 brightest cluster (BCG), 7 elliptical, and 15 S0 galaxies in order to study their stellar populations and investigate their relationship to one another. We find that BCGs follow the same relationship between central Mgb line-strength and central velocity dispersion found for ellipticals while the S0 galaxies show significant scatter with respect to this relation. Brightest cluster galaxies are in agreement with the known trend towards more massive ellipticals having larger [Mg/Fe] ratios while the internal gradients within our BCG and E galaxies are consistent with a roughly constant [Mg/Fe] ratio. We find that a correlation exists between the central [Mg/Fe] ratio and average Hβ line-strength in the sense that BCG and E galaxies with larger [Mg/Fe] ratios have lower Hβ strengths. For our BCG and E galaxies, Hβ is the best predictor of [Mg/Fe] ratio. The Mgb metallicity gradients for BCGs and ellipticals are similar and consistent with a reduction in the mean metallicity of the stellar population by about a factor of 2 over a factor of ten in radius. No strong correlations are found between the metallicity gradient sizes and either kinematic or line-strength parameters of the E and BCG galaxies. The S0 disks display roughly constant Mg, Fe, and Hβ line-strengths with radius indicating that they have uniform age and metallicity throughout. S0 galaxy minor axes ‘bulge’ metal line-strength gradients are similar to elliptical gradients and fall to values lower than those found in the disks.
Synthetic Spectra for Single-Aged Populations
Authors: Milone A. , Barbuy B.
Published: June 2019

Spectra of single-aged old stellar populations of metallicities in the range −1.0 ≤ [Fe/H] ≤ +0.5 are built in the wavelength range 6950-7550 Å including TiO bands, by combining synthetic spectra of individual stars. Two approaches are applied: one for moderately metal-poor populations, entirely based on isochrones, and the other one applied to the metal-rich Galactic globular clusters, based on isochrones for the main sequence and data of observed colour-magnitude diagrams for the evolved stages. Abundance ratios of [α/Fe] = +0.3 are adopted for populations of [Fe/H] = −1.0, −0.5, and both 0.0 and +0.3 for the more metal-rich ones.