bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Observing Station at the PIC Du Midi Observatory for the Absolute Calibration of Stellar Radiation
Authors: Peyturaux Roger H.
Published: June 2019

A new observing station designed for the absolute calibration of stellar and solar radiation has been built in the last few years at the Pic du Midi Observatory, France, at an elevation of 2860 meters. The stellar observations may begin next summer. The main improvements with respect to the calibration experiments carried out during the last decades are the use of a new type of blackbody source and an optical arrangement which is free of systematic errors in the measurements of the star/blackbody ratio. The aim of the experiment is to establish a set of homogeneous standards (about 10 B and A stars) covering the whole northern sky.
On the Calibration of the Uvby Photometric System for Late-Type Stars
Authors: Ardeberg A. , Lindgren H.
Published: June 2019

An attempt has been made to calibrate the indices of the uvby photometric system in terms of MK classes equal to and later than that of the Sun. Results are presented for stars of luminosity classes V and III; b-y and c1 data are given. For stars on the main sequence, the relation between m1 and b-y is discussed for stars of solar type.
The Response Function S(λ) of the UBV Color System - A Problem Again and Again?
Authors: Lamla Erich E.
Published: June 2019

By comparing the numerical data for the response functions of the UBV color system originally given by Matthews and Sandage (1963) with the improved functions published by Ažusienis and Straižys (1969), taking into account of the extinction values given by Melbourne (1960), the response function of U and B is found corrected for a printing error and other mistakes.
Lte-Blanketed and Unblanketed Models for SDO Stars
Authors: Rossi L.
Published: June 2019

Sd0 stars have particular importance in astrophysics due to their position in the HR diagram between the hot horizontal-branch stars and the precursors of the white dwarfs. A careful determination of their parameters is therefore highly desirable.
The Neutral Halo in the Inner Galaxy
Authors: Lockman Felix J.
Published: June 2019

Neutral gas extends out of the disk to form a modest halo over most of the inner Galaxy except for the area at R ≲2.5 kpc. The HI halo probably consists of several populations including a relatively quiescent layer and a cloudy component that has peculiar velocities. This latter component often appears between 150 and 400 pc from the plane. Most of the neutral gas at |z| ≳500 pc has the same kinematics as the gas below it.
Hot Gas in the Disk, Halo, and Disk-Halo Interaction
Authors: Cox D. P.
Published: June 2019

The interstellar medium and its hot gas component are very different from common conception.
The High-Latitude Sky at IR, Optical, and UV Wavelengths
Authors: Désert F. X.
Published: June 2019

We review the current data on the not-so-dark sky covering infrared, visible and ultraviolet wavelengths. Here, we are mainly concerned with the emission from the interstellar gas and dust above and below the galactic plane. Zodiacal light is not discussed in detail and emission from unresolved stars is briefly mentioned. Recent improvements in these studies have been made with the use of new satellite UV data, the use of high-performance CCD in the visible spectrum and extensive analyses from the Infrared Astronomical Satellite (IRAS). We show that cirrus clouds which subtend a large solid angle at high galactic latitudes are made of neutral gas and dust, are within a few hundred parsecs of the Sun, and are almost optically thin up to UV wavelengths. The brightness of these clouds, expressed as vIν = λIλ, is estimated to be within 10–8 and 10–7 W m–2 sr–1 at almost all wavelengths from λ = 0.1 to 300 μm and peaks at 150 μm, for a typical column density of 3 × 1020 H cm–2. They may yield the fundamental limitation to all extragalactic and halo studies.
NGC 891: A Summary of Observations
Authors: Allen R. J. , Sukumar S.
Published: June 2019

Three questions are posed, the answers to which are relevant to our understanding of the physical processes which shape the radio continuum morphology of normal spiral galaxies. Observations of the edge-on galaxy NGC 891 have been made for many years by several groups with the intention of contributing at least partial answers to these questions. We review here the work which we have recently done on this subject.
The Diffuse Ionized Gas Perpendicular to the Plane of NGC 891
Authors: Dettmar R.-J. , Keppel J.W. , Roberts M.S. , Gallagher J.S.
Published: June 2019

Hα images and long-slit spectra of NGC 891 show the presence of a thick layer of diffuse ionized gas (DIG) in this edge-on galaxy. Hα emission originating in the DIG of NGC 891 is detected out to several kpc above the midplane with a typical scale height for the electron density ne(z) of he~ 600 pc. The distribution of the gas is very inhomogeneous with a large scale asymmetry and filamentary structure. Individual Hα emitting structures can be traced out to 4-5 kpc above the midplane. The emission line ratios of [NII] and [SII] to Hα vary with height above the disk. We compare these properties with the analogous gas phase in our Galaxy.

The distribution of the DIG is related to star formation in the underlying galactic disk and we conclude that in NGC 891 the interstellar medium is heavily effected by processes related to star formation.
Slow Rotation of Gas in the Halos of Edge-on Galaxies M82 and NGC 4631
Authors: Sofue Y. , Nakai N. , Handa T. , Golla G. , Reuter H.-P. , Wielebinski R.
Published: June 2019

The rotation velocity of molecular gas in the halos of M82 and NGC4631 decreases with the height from the galactic plane. The slower rotation of halo gas can be explained if the gas is supplied from the central region of the galaxies due to some ejection.
Some Problems for Galactic Hydrostatic Equilibria
Authors: DE BOER H.
Published: June 2019

Although locally a static, stable equilibrium seems consistent with observations of the interstellar medium (ISM), the extrapolation towards other galactic regions is not straightforward. Basically, the variation with galactic radius of the gravitational acceleration cannot be reconciled with the approximate constancy of the HI scaleheight. Moreover, halo gas located in the outer galaxy is prone to thermal instability and subsequent collapse towards the galactic plane.
Cosmic ray powered Fountains and Winds
Authors: Völk H.J.
Published: June 2019

The dynamics of galactic halos is discussed with special emphasis on the role of Cosmic Rays. Whereas Cosmic Rays should at best play a minor role for galactic fountain flows they appear essential in driving a wind from galaxies like ours. Active galaxies with a very hot interstellar medium (T ≥ 107K) have winds due to the thermal gas alone.
The X-ray Appearance of Supernova Remnants in Tenuous Media
Authors: Cioffi Denis F.
Published: June 2019

By estimating the X-ray intensities of old supernova remnants in the disk-halo interface, deductions can be made about the ability of isolated supernovae to have created a coronal halo.
Dynamical Implications of Diffusive and Convective Cosmic ray Propagation in Galactic Halos
Authors: Breitschwerdt D. , Mckenzie J.F. , Völk H.J.
Published: June 2019

On the basis of our present knowledge about Cosmic Ray (CR) propagation, it is argued that galactic halos should mainly consist of two parts, namely a lower region, extending from the disk-halo interface to a few kpc, in which CR diffusion prevails and an upper region, where convection dominates. The upper part is the possible site of galactic wind formation due to the strong coupling of the CRs to the thermal plasma via (mainly outwards propagating) Alfvén waves as a mediator. In the lower halo and also in the disk, the gas will be effectively static, the wave field will be almost random in its direction (due to stochastic gas motions), and the CRs must diffuse through the gas to escape. We present a model that describes both the upper and the lower halo and briefly discuss simple analytic solutions for the diffusion and numerical results for the convection region.
Large-scale Gas Dynamical Processes Affecting the Origin and Evolution of Gaseous Galactic Halos
Authors: Shapiro Paul R.
Published: June 2019

Observations of galactic halo gas are consistent with an interpretation in terms of the galactic fountain model in which supernova heated gas in the galactic disk escapes into the halo, radiatively cools and forms clouds which fall back to the disk. The results of a new study of several large-scale gas dynamical effects which are expected to occur in such a model for the origin and evolution of galactic halo gas will be summarized, including the following: (1) nonequilibrium absorption line and emission spectrum diagnostics for radiatively cooling halo gas in our own galaxy, as well the implications of such absorption line diagnostics for the origin of quasar absorption lines in galactic halo clouds of high redshift galaxies; (2) numerical MHD simulations and analytical analysis of large-scale explosions and superbubbles in the galactic disk and halo; (3) numerical MHD simulations of halo cloud formation by thermal instability, with and without magnetic field; and (4) the effect of the galactic fountain on the galactic dynamo.
Secular Variations in Optical Observations of Planets: Summary
Authors: Seidelmann P. K.
Published: June 2019

The conversion in 1984 from constants, reference frames, time scales, and ephemerides, all essentially based on theories and constants by Newcomb, to the IAU 1976 system of constants, new definitions of time scales, FK5 reference system, and integrated ephemerides has produced the expected accuracy improvements. These changes included a correction to the precession constant of 1.13 arcseconds per century, a correction to the equinox motion of the FK4 of 1.23 arcseconds per century, and a new expression for the Greenwich Mean Sidereal time.
Numerical Simulations of Dense Collisional Systems with Extended Distribution of Particle Sizes
Authors: Salo H.
Published: June 2019

The dynamical evolution of dense planetary rings, such as Saturn's rings, is mainly governed by the mutual impacts between macroscopic icy particles. The local equilibrium state is determined by the energy loss in partially inelastic impacts and the viscous gain of energy from the systematic velocity field. Due to frequent impacts the time-scale for the establishment of local energy equilibrium is very short, as compared to the time-scale for radial evolution, which is determined by viscous spreading, and in some cases also by the angular momentum exchange with external satellites. Therefore, local and radial behaviour can, to a large extent be studied separately. This fact is utilized by the local simulation method (Wisdom and Tremaine, 1988; Salo, 1991), following the orbital evolution in a small co-moving region inside the rings with periodic boundary conditions. Compared to previous simulation methods (Salo, 1987) this enables much higher surface density. With the presently attainable number of particles (up to several thousands), realistic modeling of dense regions is possible, taking simultaneously into account the particle size distribution, rotation of particles, as well as vertical self-gravity. By combining several local simulations with different surface densities, it is possible to deduce the expected radial behaviour as well.
A Collisional and Self-Gravitational Model to Simulate Numerically the Dynamics of Planetary Disks
Authors: Gama Filomena Pereira , Petit Jean-Marc , Scholl Hans
Published: June 2019

The dynamical evolution of the planetary rings is simulated by means of a numerical model in which particles interact through mutual attraction and inelastic collisions. We use a mixed simulation: a deterministic integration of the N - body problem for large distances (“particle-mesh” method with an expansion of density and potential in spherical harmonics) and a Monte Carlo treatment for the close encounters. The implementation is done in the Connection Machine in order to be able to make a detailed simulation using a greater number of particles (of the order of 105). The deterministic calculation of the action of a shepherding satellite on the particles will allow us to study the effect of resonances on the formation and the evolution of the sharp edges of the rings.
A Determination of the Mass of (704) Interamnia from Observations of (993) Moultona
Authors: Landgraf W.
Published: June 2019

On 1973 November 23, there was a close approach (0.013AU) between (704) Interamnia as the fifth largest minor planet, and (993) Moultona. It was made an attempt to determine the mass of Interamnia from its perturbations on the motion of Moultona, using 82 right ascensions, 72 declinations, and of 1 observation the portion normal to the apparent motion, from altogether 95 observations from 22 oppositions 1923 January to 1991 February with a mean error of 0.″51. For the mass of Interamnia was obtained a result of 0.37 ± 0.17 · 10-10 solar masses. Although its uncertainty, this result gives an independent information about the mass of Interamnia besides the estimation from the diameter and the suspected density, considering the uncertainty of these parameters.
Periodic Solutions for the Eccentricity and Inclination First Order Resonance
Authors: Nitto Marisa A. , Sessin Wagner
Published: June 2019

For the first order resonance, the problem of the motion of two small masses around a primary body can be of three different types: eccentricity, inclination or eccentricity-inclination. The eccentricity type resonance problem has been the subject of several works since Poincaré(1902). The inclination type resonance problem was studied by Greenberg(1973) who used a particular reference system to obtain an integrable auxiliary system. Sessin and Ferraz-Mello(1984) studied the eccentricity type resonance problem considering the eccentricities of the orbits of the two small masses. Sessin(1991) study the inclination type resonance problem for an arbitrary reference system. In this paper we will study a dynamical system that includes both types of resonance. This study is based in the models developed by Sessin and Ferraz-Mello(1984) and Sessin(1991). The resulting system of differential equation is non-integrable; thus, the families of trivial periodic solutions are studied.
IUE Observations of the Bipolar Planetary Nebula NGC 2346
Authors: Feibelman W. A. , Aller L. H.
Published: June 2019

The nucleus of NGC 2346 (=PK 215 + 3°1; α = 7h06m49.S7, δ = −0°43′29″, 1950) was recently discovered by Kohoutek (1982a,b) to be an eclipsing binary with a deep (~ 2.m2) minimum in the visible and an orbital period of 17.2 ± 0.4 days. We observed NGC 2346 with the IUE on 4 occasions between 1982, Feb. 24 and May 13 and obtained 6 SWP and 4 LWR low dispersion spectrograms. These were taken at different phases, using the large entrance aperture centered on the nucleus.
Infrared Spectroscopy of the Transition Objects CRL 618 and CRL 2688
Authors: Beck S.C. , Beckwith S.V.W.
Published: June 2019

We have observed CRL 618, an infrared object believed to be in transition between the red giant and planetary nebula stages, in seven lines of vibrationally excited H2 and the Brackett α and γ lines of ionized hydrogen. The H2 observations were made in 1979 and repeated in 1982, extending over more than four years monitoring of H2 emission from this source. The intensity of H2 emission approximately tripled between August 1977 and November 1979 and may have increased by another 15-20 per cent between November 1979 and February 1982. This increase in emission occurred during the same time period that the radio free-free flux roughly doubled (Kwok and Feldman, 1981). The object may now be in a more quiescent phase following a strong flare. The H2 lines appear to be in thermal equilibrium at ≈ 2000 K and to suffer only small extinction. The Brackett α and γ lines are more heavily obscured, with ≈ 2 mag. of 2.17 μm extinction. These results support the model that the compact H II region is behind and expanding into the dense molecular material where the H2 is found. The mass of hot H2 is, ≈ 4 × 10−4 M and of total ejecta ≈ .1 M⊙, so the mass-loss rate is probably > .
Ionization Equilibrium in Models of Planetary Nebulae
Authors: Péquignot Daniel
Published: June 2019

A critical picture of the results obtained by means of photoionization models during the 70's is presented. Some reasons for the relative failure of these modellings are advanced and a new perspective is proposed for future investigations.
Charge Exchange Reactions in Astrophysical Plasmas
Authors: McCarroll R. , Valiron P. , Opradolce L.
Published: June 2019

A review is presented of charge exchange reactions of multiply charged ions with atomic hydrogen and helium at thermal-eV energies, typical of the physical conditions encountered in planetary nebulae. The basic features of the processes are analyzed in the framework of the molecular model of atomic collisions. A discussion is given of the different theoretical approaches to the calculation of the collision cross sections. A comparison with recent experimental data is included.
Red Giants as Precursors of Planetary Nebulae
Authors: Renzini Alvio
Published: June 2019

Several physical processes taking place during the red (super)giant phase of intermediate-mass stars have direct observational consequences for the subsequent nebular stage. These processes include: the regular wind and the envelope ejection, the thermal pulses during the AGB phase, the dredge-up processes, and the dust formation in expanding circumstellar envelopes. In this paper it is briefly discussed how such processes affect the mass range of PN nuclei and their evolution, and the PN lifetime, composition and dust content. The last section is devoted to a cursory discussion of PNe which can be generated by binary stars.
Mass-Loss from Late-Type Stars: New Observational Evidence
Authors: Wannier P. G. , Sahai R.
Published: June 2019

Rapid mass-loss is observed in many late-type stars, yet the mass-loss mechanisms operating are not well understood. A survey of molecular emission from circumstellar shells has been carried out using millimeterwave molecular lines and suggests that radiation pressure alone may be inadequate to explain the observed mass-loss, especially in the case of carbon-rich objects which may display rates in excess of 10−5 M⊙/yr. Recent near-IR molecular line observations provide evidence for ejected material at several different velocities along the line-of-sight and may indicate the additional mass-loss mechanism at work. Resonantly scattered IR radiation spatially displaced from the central IR continuum source has now been observed for the first time and sheds new light on the IR absorption-line results, providing information about material within 1016 cm of the central star. These results are discussed along with recent high-resolution millimeterwave observations.
Influence of the Stellar Wind on the Nebular Ionization in NGC 1535 and 4361
Authors: Adam J. , Köppen J.
Published: June 2019

The high excitation planetaries NGC 1535 and 4361 were observed with IUE satellite in the short wavelength region at high dispersion. In NGC 1535 we found P Cygni profiles of NV 1238, 1242 and OV 1371 lines with a terminal wind velocity of about 2000 km/sec. In NGC 4361 these lines are narrow absorption lines (width 0.5 Å), probably of photospheric origin.
Non-LTE Model Atmosphere Analysis of Central Stars
Authors: Méndez R.H. , Kudritzki R. P. , Simon K. P.
Published: June 2019

This review will be concentrated on the determination of the main atmospheric parameters (Teff, log g, helium abundance) of PN nuclei, and of other subluminous objects, by fitting the observed absorption line profiles with theoretical profiles obtained from non-LTE model atmosphere calculations.
Physical Properties of the Central Stars of Planetary Nebulae in the Magellanic Clouds
Authors: Stecher T.P. , Maran S.P. , Gull T.R. , Aller L. H. , Savedoff M. P.
Published: June 2019

Absolute flux distributions in the ultraviolet continua of the central stars of three planetary nebulae of known distances have been derived from observations made with the International Ultraviolet Explorer. The observations confirm the existence of planetary nebulae nuclei with masses of ≈1M⊙ and indicate that the progenitors of the nebulae were carbon stars near the theoretical upper luminosity threshold of Mbol = −6.5. The derived masses, luminosities, and temperatures of the three stars indicate that they are currently on horizontal tracks in the HR diagram and probably have not yet attained their maximum luminosities. The present luminosities (≈ 4 × 104 L⊙) each are well above the Eddington luminosity for an 0.6 Mo star. The derived properties of the stars and associated nebulae (LMC P40, SMC N2, SMC N5) are consistent with a nebular ejection mechanism that involves radiation pressure on carbon grains.
A Radio Search for Galactic Center Planetary Nebulae
Authors: Isaacman Richard
Published: June 2019

This review summarizes the techniques and results of a λ21cm and λ6cm search with the Westerbork telescope for planetary nebulae within 2° of the galactic center. After accounting for background sources and compact HII regions it appears that there are ~ 300 planetaries within 300 pc of Sgr A. This is consistent with a galactic population of ~ 21000 and agrees with the birthrate of white dwarfs. The surface density of galactic center planetaries falls off with galactic latitude approximately as b−1 and is best accounted for by a bulge with a mass of 1 X 1010 M⊙.
Planetary Nebulae in the Magellanic Clouds
Authors: Jacoby George H.
Published: June 2019

The identification and masses of Magellanic Cloud planetary nebulae are discussed. The masses are shown to be uncertain and should not be directly compared to values for galactic planetaries.

The kinematics suggest that the planetary nebulae belong to a younger rather than an older population. Abundance analyses show the Magellanic Cloud planetaries to be deficient in most elements, but the abundances of helium and carbon are comparable to values found for galactic planetaries.
Planetary Nebulae and the Chemical Evolution of Galaxies
Authors: Serrano Alfonso
Published: June 2019

Tinsley (1978) has done an excellent review that illustrates the methods and concepts that can be developed to assess the effects of planetary nebulae (PN) on the long-term history of the galaxy. Tinsley concluded that research in PN could put constraints on the past rate of star formation and provide information on chemical enrichment by low mass stars.
Kinematics of Abell 30
Authors: Reay N.K. , Atherton P.D. , Taylor K.
Published: June 2019

We have obtained seeing limited spectra of the (OIII) λ 5007 Å line at a velocity resolution of 18 km s−1 over the envelope of Abell 30.
Ionic Abundances of S III, O IV and NeV from Infrared Observations of Fine Structure Lines in eight Planetary Nebulae
Authors: Shure M.A. , Herter T.L. , Houck J.R. , Briotta D.A. , Forrest W.J. , Gull G.E. , McCarthy J.F.
Published: June 2019

The Kuiper Airborne Observatory has been used to make measurements of the infrared forbidden lines of (SIII) 18.72μm, (NeV) 24.28μm and (OIV) 25.87μm in eight planetary nebulae. In all cases the beam was larger than the emitting region. The observed line fluxes are used to determine ionic abundances under the assumption of constant density throughout the relevant volume as determined by optical observations. In some cases the NeV near UV lines are used in conjunction with the infrared measurements to determine the electron temperature in the NeV emission regions. The (SIII) 33.47μm line can be used with the (SIII) 18.72μm line flux to characterize the clumping within the nebulae.
Observations of the 3.3μm Emission feature in Planetary Nebulae
Authors: Martin W.P.J.
Published: June 2019

Absolute fluxes of the 3.3μm features were measured for 12 planetary nebulae. Both narrow-band photometry and low resolution spectrophotometry were used. Photometry was performed with narrow bandpass filters centered at 3.28μm and 3.72μm(λ/Δλ = 14). Using a CVF spectrophotometer, the 3.1μm – 3.8μm spectra of four nebulae (IC 418, IC 2149, NGC 6543, NGC 6572) were obtained. The values of the fluxes measured with the two different methods agree well.
Profiles and Intensity Ratios of the C IV λ1548, 1550 Emission Lines in Planetary Nebulae
Authors: Feibelman W. A.
Published: June 2019

The C IV resonance doublet at λ1548, 1550 is an important diagnostic tool in the study of planetary nebulae. The predicted theoretical intensity ratio of 2:1 is, however, rarely observed in high dispersion IUE spectrograms. The observed values for a sampling of 15 objects of differing excitation class range from a low of 0.74 to a high of 1.99. Variations in optical thickness, extinctions due to nebular dust, and interstellar absorption have been proposed as the cause for the deviation. Line profiles for the C IV doublet vary for different nebulae, encompassing a wide range of shapes which include: 1) narrow symmetric (Gaussian) profiles, 2) wide symmetric, 3) asymmetric with steep blue edge and extended red wing, 4) asymmetric with steep red edge and extended blue wing, 5) P Cygni profiles, 6) split peaks due to expansion velocities, and 7) multiple peaked or chaotic line structure. In addition to the main features, occasionally weak (subsidiary or ghost?) features occur that do not agree in intensity with the main line ratios but are not attributable to lines of other ions. Ultraviolet radial velocity displacements are in good agreement with optical data. Similar diversity in profiles and intensity ratios have been observed in protoplanetary nebulae and symbiotic stars. (Paper to appear in Astron. Astrophys.)
Chemical Composition of the Peculiar Planetary Nebula YM29
Authors: Kwitter K. B. , Jacoby G. H. , Lawrie D. G.
Published: June 2019

YM29 is a nearby, filamentary, low surface brightness nebula whose spectrum exhibits lines of both high and low excitation. Johnson and Rubin (1971, Ap. J. 163, 151) observed YM29 as a weak radio source; despite uncertainties as to the thermal nature of the radio spectrum and their lack of a good optical spectrum, they classified YM29 as a peculiar planetary nebula. Based on photographic spectra, Liebowitz (1975, Ap. J. 196, 191) has reported that in YM29 the (N II) lines at λλ 6548, 6584 are several times the strength of Hα.
The Maser Strength of OH/IR Stars, the Evolution of Mass loss and the Formation of a Planetary Nebula
Authors: Baud B. , Habing H. J.
Published: June 2019

From observations we find that the OH luminosity LOH of an OH/IR star increases with R2, where R is the size of the masing region. From this correlation we deduce that the mass loss rate M, the expansion velocity ve and LOH are related by LOH ~(M/ve)2. Next we consider the large range that is observed in LOH and the steep OH luminosity distribution for OH/IR stars. Both facts can be explained by the postulate that these objects undergo accelerated mass loss, and thus steadily increase their OH luminosity. We propose that OH/IR stars are at the extreme end of the Asymptotic Giant Branch and that many of them are in the process of blowing off their entire envelope in a superwind phase. Their mass loss rate during this superwind, as deduced from OH observations of the circumstellar shell, is given by a simple modification of the Reimers equation. This modification connects the superwind continuously to the Reimers wind and it provides observational evidence for the formation of a planetary nebula.
Catalogue of Central Stars of Planetary Nebulae
Authors: Acker A.
Published: June 2019

The catalogue contains 460 nuclei of 393 true and 67 possible planetary nebulae; 87 of these were discovered after the publication in 1967 of the catalogue of planetary nebulae of Perek and Kohoutek.
Distance Determinations from 21 cm Interstellar Absorption-line Measurements
Authors: Pottasch S.R. , Gathier R. , Goss W.M.
Published: June 2019

HI observations at 21 cm have been made with the Westerbork Synthesis Radio Telescope in the direction of six planetary nebulae located in or near the galactic plane (N 7027, 2440, 6537, 6572, 7026, 7354).
Velocity Dispersion and Luminosity Function of Planetary Nebulae in the Nuclear Bulge of M31
Authors: Lawrie D. G. , Ford H. C.
Published: June 2019

We used a sequence of velocity-modulated photographs to find and measure the radial velocities of faint planetary nebulae in the center of M31. The photographs were made with a Velocity Modulating Camera (VMC) which consists of a temperature-tuned 2.1 Å (FWHM) (O III) λ 5007 interference filter, a cooled, two-stage image intensifier, and a calibrating photomultiplier. The camera was mounted at the Cassegrain focus of the Shane 3 m telescope at Lick Observatory. We identified 19 new planetary nebulae, bringing the total number of known planetaries within 250 pc of M31's nucleus to 45. From the plate series, we derived radial velocities and relative brightnesses from 32 of the nebulae and placed radial velocity limits on the remaining nebulae in the field. By applying the method of maximum likelihood to the observed radial velocity distribution, we derive a mean heliocentric velocity of −309 (±25) km s−1 and a velocity dispersion of 155 (±22) km s−1 for the planetary nebulae.
Spectroscopy of Extragalactic Planetary Nebulae in the Ultraviolet
Authors: Gull T.R. , Maran S.P. , Stecher T.P. , Aller L. H.
Published: June 2019

Three high-excitation planetary nebulae in the Magellanic Clouds were successfully observed with the International Ultraviolet Explorer. Emission lines as well as nebular and stellar continua were detected. Fluxes in the lines 1550 C IV, 1640 He II, 1663 O III, and 1909 C III were measured in spectra of LMC P40, SMC N2, and SMC N5 obtained with the IUE short wavelength spectrograph; 2422 Ne IV was measured in P40 with the long wavelength spectrograph. The data were analyzed together with groundbased observations by Aller in order to derive ionization models and the nebular abundances of He, C, N, O, S, Ar. The C abundances are as large as those typically found in galactic planetaries, although the interstellar media of the Clouds are notably deficient in C. Thus, the C was synthesized in the progenitor stars and presumably was lifted to the stellar envelopes by convection prior to the ejection of the nebulae. Other planetary nebulae in the Clouds, as well as the planetary nebula in the Fornax galaxy, may be observable with IUE.
Dense Cores and Young Stars in Dark Clouds
Authors: Myers Philip C.
Published: June 2019

Dark clouds within a few hundred pc of the Sun contain hundreds of condensations with typical size 0.1 pc, density 104 molecules per cubic cm, mass 1 M⊙, and temperature 10 K. These “dense cores” are defined by maps of molecular lines, such as the (J,K)=(1,1) line of ammonia at 1.3 cm wavelength. They are associated with regions of opaque visual obscuration, groups of T Tauri stars, and other cores. They are closely correlated with steep-spectrum, low-luminosity (1-10 L⊙) IRAS sources! of about 60 cores with ammonia maps, half have an IRAS source within one map diameter. Thus cores form low-mass stars, which are probably precursors of T Tauri stars. Simple models indicate that time for a core to wait before collapsing, to collapse and form a star, and to disperse are each of order 105 yr. Cores with stars have broader lines and bigger velocity gradients than cores without stars, suggesting interaction between the star and the core due to gravity and/or outflow. Stars in cores have about 30 mag greater circumstellar extinction, and greater likelihood of CO outflow, than stars near, but not in, cores. Models of the 1-100 μm spectra of stars in cores suggest that inside of ∼100 A.U., the typical star suffers relatively little line-of-sight extinction but is accompanied by a source of significant luminosity at 5-25 μm. Models involving circumstellar disks provide good fits to the observed spectra.
Repeated Multiple-Frequency VLA Surveys of the ρ Ophiuchi Cloud
Authors: Montmerle T. , André P. , Feigelson E. D. , Stine P. , Bouvier J.
Published: June 2019

Our goal was to look for radio non-thermal emission from active PMS stars, as suggested by the presence of numerous, highly variable X-rays sources in the cloud (Montmerle et al. 1983), and by optical periodicities probably linked with starspots (Bouvier and Bertout, in prep.). Previous radio surveys have been done by Brown and Zuckermann (1975), and Falgarone and Gilmore (1981). Emission mechanisms are mainly thermal (free-free, from H II regions, winds, accretion flows; gyrosynchrotron), and non-thermal (gyrosynchrotron from flares; synchrotron in winds, White 1985; corotating interaction regions, Mullan 1984).
Observation of the Large Scale Structures of Dark Clouds
Authors: Tomita Yoshio
Published: June 2019

Owing to the drastic progress in infrared and radio observations of molecular cloud cores, the scenario of starformation seems to have been almost completed. However, the study of dark clouds as a whole, which is a stage of the starformation drama, is observationally insufficient. In order to understand the environment of a starforming region, it is important to study the large scale structures of dark clouds. And that gives the information about formation and destruction mechanism of dark clouds.
Stellar Kinematics in Star-Forming Regions
Authors: Mathieu Robert D.
Published: June 2019

High-precision radial-velocity studies of four star-forming regions: λ Orionis, NGC 2264, the Trapezium cluster and Taurus-Auriga, are completed or in process (in collaboration with Latham, Marschall and Hartmann). Single-order (∼ 50 Å, central wavelength 5200 Å) echelle spectra have been obtained for late-type pre-main sequence stars. Measurement errors of 0.7 – 1.5 km/sec are typical, although some stars do not permit any radial-velocity measurement due to stellar rotation or spectral peculiarities.
Star Formation in Taurus, the IRAS View
Authors: Harris Stella
Published: June 2019

In the course of its short existence the IRAS database has already proved an incredibly powerful tool for studying the classification of sources -both galactic and extragalactic- in a new and very exciting way. For the first time it is now possible to employ selection criteria based purely on the infrared properties of a complete (to very low intensities) and unbiassed infrared sample - thereby eliminating the selection biases which have critically limited any such previous classifications.
Cyanoacetylene Observations of B335
Authors: Hasegawa Tatsuhiko , Kameya Osamu , Hirano Naomi , Seki Munezo , Takakubo Keiya
Published: June 2019

B335 is now recognized as the smallest isolated star forming region. The detection of a Far-IR source and a bipolar flow were succesful, on the other hand, the distribution of the quiet gas is poorly understood. We are trying to determine the density distribution in B335. As the first step, we have carried out HC3N (J = 5-4 and 4-3) observations of B335. The observations of the J = 5-4 line have revealed a high density core with a 30″-60″ size. The Far-IR source is located just at the center of the core, and the core lies at the center of the bipolar flow. A mean hydrogen molecular density in the core of about 5x104 cm−3 is derived from the line ratio J – 5-4/4-3.
CO Observations of a Cometary Globule in IC1396
Authors: Nakano Makoto , Tomita Yoshio , Ohtani Hiroshi , Ogura Katsuo , Sofue Yoshiaki
Published: June 2019

A cometary globule in IC1396 named ”comet tail 6” by Osterbrock (1957), has been observed at CO and 13CO (J = 1-0) lines with a high spatial resolution, 14″, with the 45-m radio telescope at the Nobeyama Radio Observatory. The resolution corresponds to a linear size of 0.05 pc at the distance of 750 pc (Matthews 1979). Two possible pre-main sequence stars, LkHα 349 and LkHα 349/c (Cohen and Kuhi 1979), associated with small nebulosities nestle in the central part of the globule. We have obtained CO and 13CO spectra long NS and EW strips which cross each other at the position of LkHα 349 and have mapped a 1.5′x1.5′ area around the globule center at 13CO. Results from the observations are summarized as follows:
CO Observations of Draco Clouds, Unusual High Latitude Clouds
Authors: Ohashi Y. , Fukui Y. , Iwata T.
Published: June 2019

Due to highly sensitive detectors and to the observers' efforts the observations of high galactic latitude clouds (HLC) have been improved in the last few years. The detection of infrared cirrus clouds, which were discovered by the IRAS (Low et al. 1984), strongly stimulated research on HLC. It is generally considered that HLC are small clouds which lie around 100 pc of the Sun (Blitz et al. 1984). This idea is consistent with their small velocity (VLSR) in the CO (λ = 2.6 mm) line.
An Optical Polarization Study of the Bok Globule B361
Authors: Seki Munezo , Hasegawa Tatsuhiko
Published: June 2019

B361 is an isolated, round-shaped globule in Cygnus. The results of FIR observations by Keene (1981) indicate that there are no internal heat sources while recent CO observations (Hiranoet al.1987) afford evidence for the existence of a few fragments in the core of the globule.
Recent Ideas on the Formation of Massive Stars in our Galaxy
Authors: Downes D.
Published: June 2019

The massive OB stars in our Galaxy form predominantly in the warm giant molecular clouds which constitute the spiral arms. The clouds are subject to a variety of mechanisms which retard or prevent further contraction, but are nevertheless able to form stable “cores”. In the regime of subsonic internal motions, the cores may be regarded as potential protostars. The formation of massive cores, which then form massive stars, may initially be determined by the statistics of fragmentation, but may then be a feedback process, once underway, due to the steep increase of the minimum Jeans' mass with increasing temperature of the surroundings. This concept is the basis for the model of bi-modal star formation, and its implications for the initial mass function and the distribution of massive stars and metallicity gradients in the Galaxy.
Fluorescent Line Emission of Molecular Hydrogen
Authors: Black John H. , van Dishoeck Ewine F.
Published: June 2019

The electric quadrupole vibration-rotation transitions of molecular hydrogen can be excited either by thermal collisions in regions of high temperature or by ultraviolet absorption and fluorescence that leaves the molecules in excited levels, v>0, of the electronic ground state in interstellar clouds located very close to hot stars. Predictions of this fluorescent emission (Gould and Harwit 1963, Black and Dalgarno 1976) have only recently been confirmed by observations in Orion (Hayashi et al. 1985) and toward the reflection nebula NGC 2023 (Gatley and Kaifu 1987). Most previous observations of the 2 μm H2 lines have been consistent with thermal excitation in shocked regions.
Relation Between Physical Environment and its Chemistry in Orion KL
Authors: Ohishi M. , Kaifu N. , Suzuki H. , Miyaji T. , Morimoto M.
Published: June 2019

Orion KL is a famous high-mass star forming region, and many investigations have studied its dynamical aspects. But the chemical aspects of Orion KL are still veiled. In this paper, from chemical and physical analysis, we show that there are differences in the chemistry among many “velocity elements” in the core of Orion KL.
A Submillimetre CO J = 3-2 Study of M17: The Interaction of an Ionization Front and a Molecular Cloud
Authors: Rainey Ruth , White Glenn J. , Gatley Ian , Hayashi Saeko , Kaifu Norio , Griffin Matthew , Cronin Nigel
Published: June 2019

We have adopted a detailed map in the CO J = 3-2 line of the M17 molecular cloud complex covering an area of about 60 square arc minutes. As well as the M17SW cloud core, the map covers the areas containing both ionization bars, and their surrounding molecular clouds. A complex dynamical picture will be presented, with evidence for fragmentation of the complex into a number of discrete clouds, as well as indications of wide-spread interaction between the ionization bars and the CO gas. The morphology revealed by the CO maps will be discussed in connection with the distributions of IR, radio and optical emission, and the overall dynamics of the whole M17 region.
Masers in SGR B2: Sites of Star-Forming Regions
Authors: Whiteoak J. B. , Gardner F. F. , Forster J. R. , Palmer P. , Pankonin V.
Published: June 2019

H2CO and OH masers in the H II-region/molecular-cloud complex Sgr B2 have been observed with the VLA and combined with other observations of OH and H2O masers. It is found that groups of the masers and compact continuum components are located along a north-south line extending across the complex. The overall alignment suggests that star formation is being triggered by a single large-scale event such as an interaction between molecular clouds.
Millimeter-Wave Mapping of the W3 Core Region at 4 and 6.5 mm
Authors: Akabane Kenji , Hirabayashi Hisashi , Sofue Yoshiaki
Published: June 2019

Radio continuum observations of the core region of the compact H II region W3 at 6.5 and 4 mm wavelengths were made using the Nobeyama 45-m telescope. The 6.5-mm map agrees with lower-frequency maps, showing a major contribution of free-free H II emission. At 4 mm an excess over the H II emission is found, which indicates a contribution from dust grains. Comparing with sub-mm and FIR data, we suggest the existence of two dust components: normal dust at 50 K, and low-temperature (7 K), large-size grains (or interstellar “stones”) in the region west of the W3 core.
Characteristics of H2CO Towards Star-Forming Regions
Authors: Dickel H. R. , Goss W. M. , Rots A. H.
Published: June 2019

Small clusters of recently-formed massive stars with their associated compact H II regions are often found embedded in the dense cores of molecular clouds. The H2CO opacity is correlated with the compactness of the H II region and is especially high for those with associated maser activity although additional factors are involved for the ultra-compact H II regions (UCH II). VLA observations of H2CO at 2 cm have been made towards the UCH II regions of W49-north. The highest H2CO opacity of 1.0 is found towards region A which does not have maser activity; yet one of the most compact region C, has an H2CO opacity of only 0.3, For these sources the integrated H2CO opacity (over the entire profile) may be more indicative of compactness. This may be due to the broader H2CO lines which can occur towards the maser regions. For example, large line widths of 10 to 12 km s−1 ate found towards W49-north G where the most intense water masers are located and towards W49-north B which has OH masers. The H2CO line with the highest 2 cm opacity of 2.5 and a narrow width of 2 km s−1 is found towards the UCH II region ON 3 which has only weak H2O maser emission.
SiO Masers in the Star Forming Regions W51 IRS2 and Sgr B2 MD5
Authors: Ukita N. , Hasegawa T. , Kaifu N. , Morita K.-I. , Okumura S. , Suzuki H. , Ohishi M. , Hayashi M.
Published: June 2019

The maser emission of the J = 1-0 lines of SiO in vibrationally excited states has been detected in two regions of massive star formation, W51 IRS2 and Sgr B2 MD5. The SiO masers apparently coincide with strong H2O masers in each source within the uncertainties of < 5″. Their velocity ranges fall within those of the nearest H2O masers (Figure 1). In W51 IRS2 the maser emission is observed only in the v = 2 state, and the upper limit of the v = 1 line (3σ) is 1/15th of the v = 2 line intensity. The v = 1 emission found in Sgr B2 MD5 is five times stronger than the marginally detected v = 2 emission (Figure 2). Their luminosities are comparable to those from the corresponding maser in Orion.
Near-IR Observations of the Sharpless Regions S269, S271, S307 and S311
Authors: Ferrari-Toniolo M. , Persi P. , Shivanandan K. , Spinoglio L.
Published: June 2019

Using an InSb photometer/spectrophotometer attached to the 1-m ESO telescope (La Silla, Chile), we searched for the near-infrared emission from the Sharpless regions S269, S271, S307, and S311. These regions appear on the Palomar Sky Survey red plates, as bright visible nebulae, and have extended radio continuum emission.
New Infrared Observations of NGC 3603
Authors: Roth M. , Tapia M. , Ruiz M. T. , Persi P. , Ferrari-Toniolo M.
Published: June 2019

NGC 3603, one of the most massive H II regions in our galaxy, shows recent star forming activity (Frogel et al. 1977; Tapia 1981; Persi et al., 1985). In this paper we report new near-infrared maps and photometric observations in the complex region surrounding Irs 9, Irs 2 and Irs 8. Most data were gathered at the 1.5-m telescope of CTIO, using an InSb photometer. Tables 1 and 2 synthesize the observations and the results of the photometry. While the low resolution K map (Figure 1) shows basically the previously reported features, the high resolution K and L maps (shown superimposed in Figure 2), show that Irs 9 is the brightest source in the field, clearly resolved from Irs 2 and Irs 8. The presence of a previously unreported source some 22″N and 5″W of Irs 2, should be further investigated. The spectral distributions derived from our measurements and from previous ones by Persi et al. (1985) strongly suggest that the 10 and 20 μm fluxes reported by Frogel et al. (1977) at the position of Irs 2, probably correspond to Irs 9. Under this assumption, Irs 9 is probably a highly reddened massive star (1 μm to 20 μm luminosity, L∗ = 2.2 × 104 L⊙) while the luminosity of Irs 2 is less than 102 L⊙. We therefore conclude that Irs 9 is a young massive star surrounded by a warm (Tdust ∼ 250 K) dust envelope; Irs 2 seems to be the less obscured part of an associated H II region, as further corroborated by the Brγ emission and the free-free like spectrum and spectral distribution, as reported by Persi et al. (1985) and in this paper.
A Giant Stellar-Wind Shell and Star Formation Near the H II Region M16
Authors: Sofue Y. , Handa T. , Fürst E. , Reich W. , Reich P.
Published: June 2019

A large radio continuum loop of diameter was discovered at G16.5+0.7 on the Bonn 2.7 GHz and NRO 10 GHz galactic plane surveys. The loop is associated with the H II region M16, and the diameter is 60 pc at a distance of 2.8 kpc. Figure 1 shows the loop at 2.7 GHz in gray scale. The spectrum is thermal and the total H II mass is estimated at 3×103 M⊙. If the loop is due to a shell of the same diameter, the mean electron density on the shell is about 4 cm−3. The total thermal energy is about 6×1048ergs. The characteristics are summarized in Table 1.
Stellar Associations and Regions of Star Formation
Authors: Mirzoyan L. V.
Published: June 2019

The genetic nature of the OB and T-Tau stars connection with stellar associations is at present beyond any doubt. They present the characteristic population of the latter. From this important observational fact follows that all young objects connected with OB and T-Tau stars also originated in stellar associations, and hence, are genetically connected with them.
Spectra of Fast J-Shocks in Dense, Star-Forming Regions
Authors: McKee C.F. , Hollenbach D. J. , Jernigan T.
Published: June 2019

Stellar winds, bipolar outflows, and supernovae generate strong shocks in molecular clouds. If the molecular gas is magnetized and weakly ionized, shocks slower than about 40-50 kms−1 (C-shocks) emit primarily in the infrared. Faster shocks, or shocks in a weakly magnetized or more highly ionized medium (J–shocks), emit primarily in the ultraviolet and are thus harder to detect in dusty regions. J–shocks in molecular gas are usually dissociative, so that molecular emission lines from such shocks are produced by molecules formed behind the shock front. Observations of fast shocks in molecular clouds can provide valuable insights into energetic events occurring within them.