bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamical Aspects of the Taurid Meteor Complex
Authors: Štohl J. , Porubčan V.
Published: June 2019

Unusually long activity of the Taurid meteor complex, extending over 3-5 months according to new estimations based on various orbital similarity criteria, has been evoking controversies about the possible origin and dynamical evolution of this unique complex of meteor streams. It even casts doubts on the reality of the extension of the complex. In the present paper orbital elements and the extension of the Taurid meteor complex are re-examined on the bases of the most precise photographic meteor orbits available from the IAU Meteor Data Center in Lund. The results are evaluated and discussed from the viewpoint of various proposals on the origin and dynamical evolution of the complex.
The Unprecedented Light Variations of NGC 2346
Authors: Méndez R.H. , Gathier R. , Niemela V. S.
Published: June 2019

The central star of the planetary nebula NGC 2346 is now well confirmed as a single-lined spectroscopic binary, with P = 16d (Méndez and Niemela 1981, Ap. J., 250, 240). Unexpected photometric variations were recently reported by L. Kohoutek (1982, IAU Circular 3667). From additional photoelectric measurements and visual estimates we have found that these variations are periodic, with the same period as the orbital motion of the A-type primary component. From previous observations we can ascertain that such variations did not exist before, and must have started in 1981. The light minimum occurs at phase 0.75, that is to say when the A-type component is moving towards us. Radial velocities measured on spectrograms obtained during the light minimum are more positive, by about 40 km s−1, than expected from the orbital motion; while the radial velocities corresponding to the light maximum agree with what is expected from the orbital motion. The spectral type of the A-type star does not change significantly as a function of brightness.
Some Recent Results from UV Observations
Authors: Seaton M. J.
Published: June 2019

UV observations with IUE have led to recognition of the importance of di-electronic recombination in PN, for the calculation of ionization equilibria and for production of the features C II λ1335 and C III λ2297.

The determination of C abundances is discussed. In high-excitation nebulae one must allow for absorption of C IV λ1549 by dust. It has been shown that C/O ≤ 0.5 for five PN with a silicate IR feature and that C/0 ≳ l for four with a SiC feature.

Dust opacities τD have been deduced from observed ratios (C IV λ1549)/(C III λ2297) and (C II λ1335)/(C I λ4267). The values obtained, τD ≃ 0.1, are consistent with the observed strength of thermal infra-red emission.

Earlier UV observations of PN were made by Pottasch et al. (1978) using ANS. Results obtained using IUE support neither their downward revisions of star temperatures nor their claim that a number of stars with TZ(He II) >> TZ (H I) are optically thick for H I.

From IUE observations it is concluded that the planetary κ 648 in M 15 has C/O = 2.4 and that its central star has a temperature of 30 000 κ and a luminosity of 1700 L⊙.
Recombination Processes
Authors: Storey P. J.
Published: June 2019

The role of resonances in the photoionization cross-sections of ions is discussed in relation to the radiative recombination coefficient. The calculation of dielectronic contributions to the recombination coefficient is reviewed for nebular conditions, and the importance of autoionizing states close to the first ionization threshold is illustrated. For those ions for which dielectronic recombination is not important at nebular temperatures, an assessment of the accuracy of the best available recombination coefficients is given.
Physical Processes in Nebular Shells and the Interpretation of Nebular Spectra
Authors: Harrington J. Patrick
Published: June 2019

Computed models are now recognized as useful tools for interpretation of the spectra of planetary nebulae. However, even the most detailed models need geometrical parameters such as filling factors which are poorly determined by observations. Some effects may be seen more clearly by modeling the stratification than by just using total fluxes. A simple model for NGC 6720 is presented which reproduces the behavior of (Ne III) λ3869 observed by Hawley and Miller (1977), clearly showing the effects of charge transfer. The behavior of C II λ4267 remains puzzling. Finally, we comment on the interaction of high velocity stellar winds with nebular shells. Non-equilibrium particle distributions at the contact between the shocked stellar wind and the nebula may result in the rapid cooling of the shocked gas.
Evolution of Unstable Red Giant Envelopes
Authors: Tuchman Y.
Published: June 2019

Two main observable phenomena are directly connected with the dynamical behaviour of Red Giant (R.G.) envelopes: The variability of Mira stars and Planetary Nebulae (P.N.) ejection.
Numerical Models of Dynamical and Spectral Evolution of Planetary Nebulae
Authors: Okorokov V. A. , Shustov B. M. , Tutukov A. V. , Yorke H. W.
Published: June 2019

Numerical models of planetary nebulae (PN) dynamical evolution are calculated under the assumption of spherical symmetry and discussed in the light of infrared, radio and optical observations. The set of hydrodynamical equations is solved simultaneously with equations for nongrey radiative transfer.
HBV 475 as a Candidate Proto-PN
Authors: Tamura S.
Published: June 2019

The symbiotic nature of this object has been investigated by optical spectroscopy and photometry in the near infrared region. There are three components, which are (i) the ionized expanding envelope consisting of two layers of low and high excitation species, (ii) the late type component corresponding to a blackbody of 2500 K and indicated by TiO absorption band, (iii) the hot remnant star whose temperature is estimated indirectly as 150 000 K or more.
Mass Loss from Central Stars of Planetary Nebulae
Authors: Perinotto M.
Published: June 2019

Stellar winds have been revealed in a large fraction of central stars of planetary nebulae from P Cygni profiles observed with the IUE satellite. The relevant lines are essentially the resonance lines NV λ 1240, Si IV λ 1397, CIV λ 1549 and the subordinate lines OIV∗ λ 1342, 0V∗ λ 1371, NIV∗ λ 1579. Edge velocities are of the order of 1000-3000 km s−1, similar to the case of population I O stars. Detailed determinations of the mass loss rate have been performed for NGC 6543, NGC 2371, IC 2149 and IC 3568 with values between 4.10−9 to 7. 10−7 Mo yr−1. The accuracy of these determinations is not well known. It is however clear from the variety of observed profiles in these and in several other objects that properties of the winds (ionization structure, etc.) varies considerably from object to object and that very likely the mass loss rate will span over a large interval. Some possible consequences of these winds are discussed.
A Powerful Method for Deriving Mass-Loss Rates from Planetary Nebulae and Other Objects: The First Order Moment W1 of Unsaturated P Cygni Line Profiles
Authors: Surdej Jean
Published: June 2019

For the case of optically thin lines, we show that the relation existing between the first order moment

of a P Cygni line profile and the quantity n (level) (cf. Castor, Lutz and Seaton, 1981), where is the mass-loss rate of the central star and n (level) the fractional abundance of the relevant ion, is in fact independent of any Sobolev-type approximations used for the transfer of line radiation. Consequently, all results established in the context of “very rapidly” expanding atmospheres (see Surdej, 1982) and mainly referring to the non-dependence of W1 on various physical (underlying photospheric absorption line, limb darkening, collisions, multiplet line transitions, etc.) and geometrical (radial and rotational velocity fields, size of the atmosphere, etc) effects remain unchanged for arbitrary (e.g. non-Sobolev type) outward-accelerating velocity laws.
IUE Observations of Central Stars
Authors: Heap Sara R.
Published: June 2019

Despite similar evolutionary histories and a common ultimate fate as white dwarfs, central stars of planetary nebulae have surprisingly diverse spectral properties. Their visual spectral types encompass all varieties known for hot stars, including Wolf-Rayet, O and Of, subdwarf O, white-dwarf, and continuous (Aller 1968, 1976), and O VI-emission types (Smith and Aller 1969, Heap 1982). Their spectroscopic temperatures range from less than 30,000°K (e.g. He 2-138, Mendez and Niemela 1979; the WC 11 stars, Houziaux and Heck 1982) to upwards to 150,000°K or more (e.g. NGC 246, Heap 1975; Abell 30, Greenstein 1981). Their atmospheres range from demonstrably helium- and carbon-rich (e.g. the WR stars, Barlow and Hummer 1982, Benvenutı et al. 1982) to apparently normal (e.g. the Of stars, Heap 1977a,b), to helium-poor (e.g. the nascent white dwarfs in Abell 7 and NGC 7293, where gravitational settling appears to have already taken effect, Mendez et al. 1981).
Planetary Nebulae in Local Group Galaxies
Authors: Ford Holland C.
Published: June 2019

Recent surveys for planetary nebulae have given the first identifications in Fornax, NGC 6822, M33, IC 10, Leo A, Sextans A, Pegasus, WLM, NGC 404, and M81, and extended the identifications in the SMC, the LMC, and M31. Observations of planetaries have established chemical compositions in old or intermediate age populations in 8 Local Group galaxies. The chemical compositions show that i) the helium abundance is higher in planetary nebulae than in H II regions in the same galaxy, and ii) nitrogen is overabundant relative to H II regions by factors of 4 to 100. Planetary nebulae are not a major source of helium in star-forming galaxies, and are a major source of nitrogen. The planetary in Fornax has a relatively high O abundance, and, together with Fornax's carbon stars, establishes the presence of at least 2 stellar populations. The abundance gradient derived from 3 planetaries in M31 is very shallow, and gives high abundances at ~ 20 kpc. By using planetary nebulae as standard candles, upper and lower distance limits have been set for 10 Local Group candidates, and a new distance estimated for M81.
High-Resolution Spectroscopy of NGC 7026
Authors: Solf J. , Weinberger R.
Published: June 2019

Up to now, the geometrical and kinematical structure of the well-known bizarre nebula NGC 7026 has not been discussed in the literature. Using the large vertical Coude spectrograph of the 2.2 m telescope on Calar Alto, Spain, we obtained long-slit spectra covering the nebula at 5 different position angles, in the ranges from 4730 to 5050 Å and from 6470 to 6770 Å. The high spectral (up to 6 km s−1 FWHM) and spatial resolution (seeing-limited ≲ 2″) reveals a rather complex structure in the lines of Hα, Hβ, (OIII) λλ 4959, 5007, HeI 6678, HeII 6560, (NII) λλ 6548, 6583, and (SII) λλ 6716, 6731. Generally, the lines exhibit a double “bowed” appearance; both components consist of several condensations of small angular extent. The velocity field suggests a non-spherical expansion of an elongated thin shell structure. The observations can be explained by an ovoidal or “bipolar” configuration of the nebula consisting of an expanding equatorial toroid (Vexp = 54 km s−1 in (SII)) and two blobs moving at higher velocities outwards along the polar axis (inclination angle with respect to the line-of-sight: 75°). The geometrical and kinematical structure observed in the lines of various excitation degrees indicates a pronounced ionization stratification and allows to derive the dependence of the expansion velocities on the radial distance inside the nebulae. No noticeable extinction within the nebula has been found. The bipolar structure of NGC 7026 resembles that of some other planetary nebulae and might be caused by an equatorial concentration of the circumstellar material lost during the late phase by the progenitor asymptotic giant-branch star. Using distances and interstellar extinctions of 48 stars within 1° of the planetary, we determined a distance of 2180 (≈ ± 700) pc for the nebula.
Radiative Transfer Effects due to Curvature and Expansion in a Dusty Planetary Nebula
Authors: Peraiah A.
Published: June 2019

We have investigated the effects due to curvature and radial expansion in a planetary nebula, with hydrogen and helium. We have solved the radiative transfer equation with spherically symmetric approximation in the rest frame. We have included dust in static as well as in expanding media. The effects on the internal sources and the mean intensities at the internal points have been calculated. It is found that the effect due to the presence of dust is to reduce the mean intensities, and curvature effects on the internal sources are more pronounced than the effects due to radial expansion of the gas.
The Formation of Resonance Lines in Gaseous Nebulae Partially Filled with Dust
Authors: Wehrse R.
Published: June 2019

The radiation field for a resonance line is calculated for a gaseous nebula which consists of a dust-free and a dust filled layer (1/2 or 1/4 of the total volume). For comparison we compute also the line profiles for corresponding homogeneous configurations, with and without dust.
Physical Conditions in the Compact Planetary Nebula Sw St 1
Authors: Cohen M. , Flower D.R. , Goharji A.
Published: June 2019

Sw St 1 is a compact and possibly young planetary nebula which has been recently observed at infra red (Aitken et al., 1979) and radio (Kwok et al., 1981) wavelengths. In the 8-13 μm region, a silicate emission feature is observed, suggesting that the nebular envelope is oxygen rich. The high emission measure determined from the radio observations implies a large value for the electron density.
The Ionization Structure of NGC 6720 and NGC 7009
Authors: Barker T.
Published: June 2019

Measurements of line intensities over a spectral range generally as great as 1300 Å to 11,000 Å have been made in four positions in the Ring Nebula and eight positions in NGC 7009. Ionic abudances determined from optical and UV lines are in good agreement, except that the C2+ abundance inferred from the optical 4267 Å recombination line is as much as 10 times higher than that measured from the 1906, 1909 Å CIII) lines. In both nebulae, this discrepancy is greatest nearest the central star. At the present time the most attractive explanation seems to be that the 4267 Å line is affected by resonance fluorescence due to light from central stars of planetaries.
Apparent Magnitudes of Planetary Nebulae Nuclei
Authors: Shaw R.A. , Kaler J.B.
Published: June 2019

B and V magnitudes for the central stars of a number of planetary nebulae are presented. The observations were obtained between 1971 and 1981 with the University of Illinois one-meter telescope at Prairie Observatory. The average magnitudes presented are accurate extractions of the stellar continuum flux from the total (stellar plus nebular) measured flux (see Kaler, 1976, Astrophys. J., 210, 113).
UBV-Observations of Variable Planetary Nebulae
Authors: Kostyakova E.B.
Published: June 2019

The UBV- and spectral observations of several variable planetary nebulae were continued at the Crimean Station of Sternberg Astronomical Institute.
Wind-Blanketed Stellar Atmospheres
Authors: Abbott D.C. , Hummer D.G.
Published: June 2019

Radiation scattered by a stellar wind back into the photosphere alters the temperature-depth relation and thus the stellar flux distribution. The fraction of the radiation returned to the star at every wavelength has been calculated using stellar wind models accounting for approximately 10 000 lines. Model stellar atmospheres containing hydrogen and helium, both with and without the assumption of LTE, have been computed allowing for the reflected radiation. For realistic wind and stellar parameters relevant to central stars of planetary nebulae, we obtain a 25% increase in the surface temperature and in the optical brightness temperature, and a 2 order-of-magnitude increase in the flux in the He II continuum.
Measurement of Magnetic-Field Strengths in Molecular Clouds: Detection of OH Line Zeeman Splitting
Authors: Kazès I. , Crutcher R. M. , Troland T. H.
Published: June 2019

We report here the first results of an extended program to measure magnetic-field strengths in interstellar molecular clouds. The very large radio telescope located near Nancay, France, has been used to measure the Stokes-parameter I and V spectra of the 1665 and 1667 MHz lines of OH in emission and in absorption from extended (non-masing) molecular clouds. Signals in the V spectra are produced by Zeeman splitting of the spectral lines; we derive magnetic-field strengths or limits from these data.
A Southern Hemisphere Ammonia Survey
Authors: Peters W. L. , Forster J. R. , Gardner F. F. , Whiteoak J. B. , Kuiper T.B.H.
Published: June 2019

A spectral line survey for interstellar NH3 is being carried out using the 64-m telescopes at Parkes and Tidbinbilla. Both telescopes are equipped with K-band masers yielding system temperatures below 100 K. The preliminary survey was to be made with the Parkes antenna (beam = 1.5′ arc) with follow-up mapping of the more interesting sources at Tidbinbilla (beam = 0.9′ arc). Sources have in general been H II regions from the H2CO surveys made at Parkes. Approximately 70 sources (out of a target of (∼ 100) have been observed simultaneously in the metastable (1,1), (2,2) and (3,3) transitions. The (1,1) line has been detected in about 70% of the sources surveyed. The other lines which involve higher excitation are detected primarily in the more compact sources, particularly those associated with OH and H2O masers. Examples are given of spectra for different types of source.
21 cm Line Study of Large Scale Density Fluctuations in the Taurus Molecular Complex
Authors: Shuter W.L.H. , Dickman R. L. , Klatt C.
Published: June 2019

21-cm spectra on a 41 × 31 grid, centered at 1950: RA 04h30m; DEC 27d00m, at points separated by a true angle of 0.25 degrees, were observed using the Arecibo telescope in October 1985. The identical grid had previously been observed in 13CO by Kleiner and Dickman (1984) with the FCRAO mm wave telescope. In this preliminary analysis we determined autocorrelation functions and power spectra for 21-cm self absorption “intensities”, for a cross passing through the central point. Both arms of the cross, aligned parallel to RA and DEC, show a power spectral peak at a frequency of 0.312 reciprocal degrees, corresponding to a period of 3.2 degrees on the sky. Assuming that the Taurus complex is at a distance of 140 pc, this corresponds to a correlation length of 7.8 pc, which is about a factor of two smaller than the value of 14 pc found by Kleiner and Dickman for 13CO.
A New Molecular Core in L1641
Authors: Takaba H. , Fukui Y.
Published: June 2019

L1641 is a large dark cloud which extends 6.3 degree2 to the south of the Orion nebula (Lynds 1962). This region contains a reflection nebula, NGC 1999, several emission line stars and Herbig-Haro objects and is thought to be a site of on-going star formation. A CO(J = 1-0) map obtained with the Nagoya 1.5 m telescope (Takano 1983) revealed that CO hot spots extend further to the north by ∼ 30′ from NGC 1999. This suggests that L1641 may contain other regions of recent star formation. Therefore, we have mapped the L1641 cloud to investigate if there are other star-forming regions in it.
The Magnetic Field Structure of the CMa R1 Star Formation Region
Authors: Vrba F. J. , Baierlein R. , Herbst W.
Published: June 2019

The CMa R1 association is embedded in a curved region of dark and reflection nebulosity which is part of a larger-scale ring structure of emission nebulosity thought to be a relatively old supernova remnant (Herbst and Assousa 1977, 1978), These investigators and Herbst, Racine, and Warner (1978) have argued that recent star formation in CMa R1 was induced by the supernova. Indeed, data for the emission ring, an associated expanding HI shell, and a nearby runaway star infer an age for the supernova remnant of 3x105 years; consistent with the age of most of the CMa R1 stars.
Comparison of CO and IR Emission of IRAS Unidentified Sources
Authors: Boulanger F. , Casoli F. , Combes F. , Dupraz Ch. , Gérin M.
Published: June 2019

IR observations with the IRAS satellite have revealed in the galaxy a lot of point-like unidentified sources: they have no optical or radiocontinuum counterpart, and cannot be known stars, nor H II regions. We have undertaken mm-wave observations of a sample of ∼ 100 of these sources with the Bordeaux telescope (beamsize = 4.4′ ∼ IRAS resolution). These sources seem to be associated with protostars or young stars still embedded in molecular clouds. Some of the sources present high-velocity wings, suggesting a bipolar gaseous ejection from the protostar.
Temperature Fluctuations and Evolution of Dust Grains in Dense Interstellar Clouds
Authors: Aiello S. , Barsella B. , Cecchi-Pestellini C. , Ferrini F. , Mencaraglia F. , Rosolia A.
Published: June 2019

Interstellar extinction studies (Chlewicki et al, 1984), as well as IR observations (Sellgren et al, 1983) require the presence in the interstellar medium of a substantial number of small (a≲0.01 μm) dust grains. The temperature of such small grains is subjected, because of their small steady-state energy, to large fluctuations as they absorb photons from the incident radiation, which could prevent the accretion on such grains (Greenberg and Hong, 1974).
Dynamic Structure of the Horsehead Nebula
Authors: Suzuki H. , Kaifu N. , Ohishi M. , Miyaji T. , Ishikawa S.
Published: June 2019

We have made a preliminary map of the Horsehead nebula in CO (J=1-0) using the NRO 45-m telescope. The HPBW is 15″, the grid spacing 10″, and the velocity resolution is ∼0.1km/s. Figure 1 shows the integrated intensity with a velocity interval 10-11.5 km/s, which we found represents well the shape of the dark globule of the Horsehead. The coincidence of the CO feature and the dark nebulocity is strikingly well, especially at the sharp edges in the south and in the west (from the neck to the ears). The quality of the data are not satisfactory, though. The typical noise level is 1 K rms in TA, and the accuracies of the pointing and the intensity calibration is rather low due to the bad weather during the observation. Some scanning effects in the intensities can be recognized in Figure 1. One of the reason why the gap obtically seen beneath the jaw is not clear in the CO map may be attributed to the pointing errors.
The Orion Star-Forming Complex
Authors: Hasegawa Tetsuo
Published: June 2019

High resolution images of the Orion Nebula in the millimeter wave emission lines of CS and CO taken with the 45-m telescope at Nobeyama are presented. They cover a field approximately 400″ square with a 15″ – 34″ resolution and reveal a wealth of information on kinematic and density structures. The images of the J=1-0 (49 GHz) and J=2-1 (98 GHz) lines of CS show a long (>1 pc) and narrow (∼0.1 pc) N-S ridge of dense molecular gas. On the ridge, two major clumps are recognized; one is associated with the KL object and the other is 100″ south of it. The images of the J=1-0 (115 GHz) CO line indicate interaction between the molecular cloud and the H II region formed by the Trapezium stars. Bright CO emission is found towards the edges of the denser part of the H II region delineated by radio continuum emission. The CO emission coincides with the emission of vibrationally excited H2 and the 3.3 μm dust emission feature. The CO images reveal filamentary structures (“streamers”) stretching radially from the KL region. On the streamers there are Herbig-Haro objects moving away from the KL region. They may be tracers of weak interaction between the ambient molecular gas and mostly unseen, highly collimated, high-velocity (>200 km/s) jets.
13CO(J = 1-0) Observations of the Orion Molecular Cloud
Authors: Sugitani K. , Fukui Y.
Published: June 2019

We present new 13CO(J = 1-0) measurements of the Orion molecular cloud. The data were taken with the 4-m millimeter-wave telescope of Nagoya University with a beamwidth of 2.7′. The high velocity resolution of 0.1 km s−1 employed has revealed significant details of the 13CO emission toward the H II region.
The Rotational Excitation of OH in Orion
Authors: van Dishoeck E. F. , Melnick G. J. , Black J. H.
Published: June 2019

The Orion–KL region has been studied extensively by observations of lines originating from highly–excited rotational levels of CO (see Watson et al. 1985). The lines arise in the shocked gas that lies at the interface of the hypersonic mass outflow of a newly–formed star and the quiescent material in Orion. The CO line intensities are sensitive to the physical conditions in the shocked region, and have been interpreted with a kinetic temperature T ≃ 600 K and density n(H2)≃ 2 × 106 cm−3. Recently, pure rotational lines of OH have been detected as well in the far-infrared spectrum of Orion. Since the OH and CO molecules differ substantially in their energy level structure and in other properties, it is of interest to investigate whether the OH excitation probes the same physical conditions as the CO excitation or whether the two molecules reside in different parts of the shock.
Expansion of Ultra-Compact H II Regions
Authors: Moran J. M. , Reid M. J. , Sams B.
Published: June 2019

The dynamical properties of the ionized envelopes surrounding massive, newly formed stars can be probed by the measurement of radio recombination lines over a wide range of frequencies. In an expanding envelope, the centroids of the radio recombination lines move progressively to lower velocities with increasing value of the principal quantum number, n. This shift is caused by the free-free absorption on the near side of the envelope combined with non-LTE radiative transfer effects.
Hollow H II Regions: From Giant to Ultracompact
Authors: Montmerle T. , Dorland H. , Doom C.
Published: June 2019

H II regions around OB associations have a thick-shell structure (see, e.g., the Carina and Rosette nebulae), and yet the standard “Hot Interstellar Bubble” model (e.g., Weaver et al. 1977) predicts thin H II shells around a large X-ray emitting volume, when associated with stellar winds. Observations suggest that strong dissipation must occur at the edge of the wind cavity: (i) expansion velocities there are much smaller than predicted by the standard model (e.g., Chu, 1983); (ii) in bubbles around WR stars, overabundances of N, He, etc., are seen, hence the need to cool these WR-produced elements down to observable temperatures (Kwitter, 1981). Also, two theoretical developments are important: (i) new stellar evolution models for massive stars, including mass loss and overshooting in convective cores (e.g., Doom, 1985); (ii) a non-linear theory for heat conduction with steep temperature gradients (Luciani et al. 1985).
A Study of Shock Excited Gas in the Supernova Remnant IC443
Authors: White Glenn J. , Rainey Ruth , Hayashi Saeko , Kaifu Norio
Published: June 2019

Extensive molecular line observations have been made of a small region of the supernova remnant IC443 that is strongly interacting with, and shocking a nearby molecular cloud. The observations obtained at the Nobeyama 45-m, Kitt Peak 12-m, and UKIRT 3.8-m telescopes include detailed maps at 15 and 30 arc second resolution in the CO (J = 1-0) and 2-1 lines, and spectra in the CO (J = 3-2) transition. The shocked gas is characterized by a low density and a high temperature. The spatial distribution of the CO shows a remarkable correspondence to maps of shocked molecular hydrogen, and contains a very complex velocity structure, indicating extensive fragmentation. The masses of the clumps are 0.1-0.3 solar masses, and as a system are dynamically unstable. In addition we report a comprehensive molecular line survey towards two of the fragments in IC443, one characterized by the presence of high velocity, and the other by low velocity gas. These results are discussed in relation to the properties of shock-excited gas and theoretical shock-chemistry models. Several other regions in IC443, which appear as strong far-Ir emitters on IRAS images of the remnant, were searched, and also found to be strong emitters of characteristic shocked-gas profiles.
Star Formation and Supernovae
Authors: Rengarajan T. N. , Verma R. P. , Iyengar K.V.K.
Published: June 2019

We have searched for associations between supernova remnants (SNR) and IRAS sources. For this purpose we used 117 SNRs from the catalogue of van den Bergh and searched the IRAS Point Source Catalogue for sources associated with SNRs and having a flux density spectrum increasing with wavelength beyond 25 m. For each SNR a square box of area 2 deg2 was searched for sources. The difference between the observed number within the SNR (with 10% radial extension) and the number expected on the basis of source density in the box excluding the SNR itself, was termed the excess. The results are shown in Table 1. There are a few SNRs which show significant excess on an individual basis. The cumulative excess of the rest has a 4 significance. For 58 SNRs with well defined maps, the data in Table 1 show that the significance of excess increases in the shell area. Figure 1 shows the excess as a function of distance to SNR. Also plotted are average excesses for different distance intervals. The increase in excess as distance decreases, strengthens the hypothesis of association with SNR, since at shorter distances, more IRAS sources will be above the threshold of detection.
Observed Characteristics of Protostellar Disks
Authors: Kaifu Norio
Published: June 2019

Detailed structures in the central parts of several star forming regions have been observed with the Nobeyama 45-m telescope. The disk and flow systems observed in L1551, R Mon, GL490 and S106 regions show the following common characteristics: (1) Double-peaked appearance with a thin central part around the IR source, (2) Cavities exist on both polar sides of the disk, and the low velocity molecular flow fits the shape of the cavity wall and the pattern of the reflection nebula. (3) The flow seems to be accelerated gradually along the wall of the cavity. An empirical model based on these results is discussed.
Models of Shock Activity in the BN-KL Region of Orion
Authors: Hollenbach David , McKee C. , Chernoff D.
Published: June 2019

The observed H2, CO, OI(63 μm), SiII(34.8 μm) and H51α emission line intensities in the BN-KL region of Orion are modeled as arising from two types of shock waves. The molecular emission arises from non-dissociative shocks with low peak postshock temperatures (< 3000 K), traveling at speeds of vs ∼ 40 km/s into ambient gas of density n0∼105-6 cm−3 and transverse magnetic field B0 ∼0.5 milligauss. The OI(63 μm), Sill(34.8 μm) and H51α emission arises in the cooling regions behind faster (∼80 km/s) dissociative shocks with high peak postshock temperatures (∼105 K) and with preshock densities n0 >3x104 cm−3.
Observations of Molecular Flows in S140 and L723
Authors: Hayashi Saeko S. , Hayashi Masahiko , Uchida Yutaka , Kaifu Norio , Hasegawa Tetsuo , Shibata Kazunari
Published: June 2019

We have made 15″ resolution observations of CO J = 1-0 emission toward L723 and S140 using the Nobeyama 45-m radio telescope. The maps resolved the molecular flow structures clearly. The outflow in the S140 molecular cloud was resolved to be a bipolar structure with its axis being nearly perpendicular to the elongation of the dense core observed in CS emission and to the direction of the infrared polarization. The blueshifted and redshifted components in L723 were resolved into two pairs of bipolar outflows with a point-symmetric structure.
Role and Evolution of Ammonia Clouds in Bipolar Flow Sources
Authors: Takano T. , Stutzki J. , Fukui Y. , Winnewisser G.
Published: June 2019

Many bipolar flow sources have been found around infrared sources with a wide luminosity range. The bipolar sources are thought to be a common stage of early stellar evolution. Recently, compact dense molecular clouds have been detected, just around the exciting infrared sources of several bipolar flow sources (e.g. Torrelles et al. 1983). An investigation of the nature of these surrounding dense molecular clouds should be important to study the acceleration and collimation mechanisms of the bipolar outflow.
Diffraction-Limited Far-Infrared Imaging of “Protostars”
Authors: Harvey Paul M. , Lester Daniel F. , Joy Marshall
Published: June 2019

New mapping and analysis techniques for NASA's Kuiper Airborne Observatory are described which permit us to obtain information of size scales of order 10″ in the far-infrared. Basically, the focal-plane image is highly oversampled while the telescope is scanned smoothly and repeatedly over the region of interest with a slit of size λ/D. Maximum-entropy deconvolution is then used to obtain spectral frequency information down to scales of ∼ λ/2D.
Collimation of Stellar Winds by the Magnetic Field
Authors: Sakurai Takashi
Published: June 2019

The pinching effect of the magnetic field is studied as a possible mechanism for collimating stellar winds into bipolar flows in star-forming regions. Axisymmetric, steady, polytropic stellar wind models are constructed by solving numerically the magnetohydronynamic equation. The magnetic field is assumed to be radial near the star. Far from the star the magnetic field makes a spiral near the equatorial plane and the toroidal components build up. The pressure and the tension of the toroidal magnetic field deflects the wind away from the equator toward the rotation axis. This deflection continues until the flow becomes nearly cylindrical near the rotation axis. This state is a pinch configuration in which dense gas is confined into a collimated flow by the toroidal magnetic field. This mechanism works under very general circumstances in the magnetic stellar winds from rotating stars.
On Early Evolution of Accreting Stars
Authors: Shustov B. M. , Tutukov A. V.
Published: June 2019

Accretion is a dominant factor in the early evolution of stars. The first time an accretion regime settles in is when a dusty opaque core forms. The mass of adiabatically contracting core inside the isothermally collapsing envelope depends only on the optical properties of dust. Spherically symmetric models of dusty cores were constructed using the Henyey technique with accretion boundary conditions (Menshchikov 1986). It appears that all protostars with normal chemical composition should pass through the stage of a quasistatic dusty core. The evolution of dusty cores is similar to that of “normal” young stars with accretion. One could distinguish convective, radiative and central core contraction phases. The life-time tc of the core depends on the core mass Mc and the accretion rate Ṁ (for Mc = 0.01 M⊙ and Ṁ = 1.6x10−6, 1.6x10−5 M⊙/year tc = 1.2x104, 3x103 yrs consequently). After dust exhaustion in the core it collapses and a central ionized quasistatic region grows in several tens of years. A flash of infrared radiation at the moment is not excluded.
The Gem OB1/IC443/S249 Complex: A Case History of Stellar Evolution
Authors: Braun R. , Strom R. G.
Published: June 2019

The extended cloud complex containing members of the Gem OB1 association, the supernova remnant IC443, and the H II region S249 has been studied with IRAS observations at 12,25,60 and 100 microns and WSRT observations at 327 and 1400 MHz and in the 21-cm H I line. A skeleton-like framework of cool dust delineates the boundaries of the region, and physical parameters have been derived for the entire complex, individual H II regions and the shocked and recombined gas within IC443 using the radio and infrared data. IC443 is shown to consist of three interconnected, roughly spherical subshells of vastly different radii and centroids. The geometry is fully constrained by the structural and kinematic data. Two of the subshells together define the usually assumed boundaries of IC443, while the third includes the optical filaments which extend beyond the northeastern rim and which are shown to have well-correlated nonthermal radio components. The available evidence implies that the SNR shock has encountered a pre-existing high density shell. It is shown that the system of subshells is fully consistent with formation by stellar wind driven bubbles generated by association members within the inhomogeneous environment of the complex.
Density Wave Related Molecular Cloud Spiral Arms in M51
Authors: Rydbeck G. , Hjalmarson Å. , Johansson L.E.B. , Rydbeck O.E.H.
Published: June 2019

Results from a continuing study (Figure 1a) of the CO (J = 1-0) distribution in M51 are presented. The angular resolution (beam size 33″ = 1.5 kpc) and pointing stability (better than 4″) of the Onsala 20-m telescope have extracted a number of new features of the molecular cloud distribution and kinematics of M51 [1,2]:
Abundances of Classical Cepheids and Evidence for Secondary Star-Formation
Authors: Giridhar Sunetra
Published: June 2019

In addition to the well-known radial abundance gradient in the disc of our Galaxy, there are indications of small-scale variations (Talent and Dufour 1979, Giridhar 1983). We have compiled spectroscopic abundances for long period Cepheids and to eliminate the effect of differences in ages, derived their places of formation by calculating their galactic orbits backwards in time. The stellar orbits were calculated considering the axisymmetric gravitational potential as well as the spiral potential due to the density wave. The parameters related to spiral waves are taken from Yuan (1969). The equations of motion in the (ζ, η, ξ) system were numerically integrated using the Runge-Kutta method and birthsites were transformed to (ζ, η) in the reference frame of the spiral pattern. The details of the computations are described by Giridhar (1985). In addition to the accepted value of 13.5 km s−1 kpc−1 for pattern velocity, birthsites were also calculated for ωp = 11.5 and 15.5 km s−1 kpc−1. Figure 1 shows the birthsites in the galactic plane for the three values of the pattern velocity. The Cepheids in the figure can be identified through the serial number in Table I which contains our compilation of Fe/H and derived birthsites. It is obvious from the figure that the systematic shifts in birthsites for different pattern velocities are not large enough to affect the assignment of birthsites to different arms.
Molecular Clouds and Star Formation Near the Galactic Center
Authors: Bally J. , Stark A. A. , Wilson R. W.
Published: June 2019

We present the results of an extensive survey of 13CO and CS emission in the inner 1 kpc region of our Galaxy. The properties of the clouds are very different from molecular clouds observed in the galactic disc: 1) The mean gas density is more than one order of magnitude higher ( = 104 cm−3). 2) The internal velocity dispersion is greater by a factor of 5 to 10 (v = 20 to 50 km s−1). 3) Many of the clouds follow highly eccentric orbits about the center. 4) This region contains roughly 10% of the Galaxy's molecular mass, but much less than 10% of the newborn massive stars. Star formation may be inhibited by the large turbulent energy content of the clouds. Some of these properties may result from the large galactic tides in the inner Galaxy. In order for a cloud to remain gravitationally bound despite the shear induced by galactic rotation, the mean gas density must be greater than  = 104 cm−3. The velocity dispersion of the gas must be large to satisfy the virial theorem. The forbidden velocities and high latitude extent of some of the emission can be explained by the presence of a stellar bar and does not require a central explosion. Some of the thermal infrared and continuum features of the galactic center can be understood as the direct consequence of cloud-cloud interactions.
Young Stellar Objects in the Large Magellanic Cloud
Authors: Epchtein N. , Braz M. A.
Published: June 2019

We present the results of a search for compact infrared objects in the direction of type I OH/H2O maser sources discovered towards H II regions in the Large Magellanic Cloud.
Infrared Triplet in the Radio Arc Near the Galactic Center
Authors: Okuda H. , Shibai H. , Kobayashi Y. , Kaifu N. , Hayashi M. , Nagata T. , Gatley I.
Published: June 2019

An infrared complex has been found in the radio arc region near the Galactic center. The complex consists of three sources that are close (< 10″) to each other, and are almost identical in every point of their characteristics; having the same energy spectrum and the same polarization. The observed polarizations are large; 5% at the K-band, and are parallel to the galactic plane. Both behaviors are compatible to those of the galactic center sources, suggesting that the sources are located near the galactic center. The energy spectra are very similar to each other, with large infrared excesses, peaking near the M-band. The luminosity of each source is estimated to be as high as 3-5x105 L⊙, after correcting for interstellar extinction assuming that they are located near the Galactic center; their luminosity is comparable to those of supergiant stars. By CVF spectrophotometry no CO-band absorption nor Brγ emission has been detected, thus no evidence for either M-supergiant nor OB supergiant has been obtained. On the other hand, the very close linear distances, 0.5 pc among each other, suggests their physical relationship, i.e., they should be very young objects, otherwise they would have been dispersed far apart.
The Interstellar Medium in Star Burst Galaxies
Authors: Genzel R. , Lugten J. B. , Crawford M. K. , Watson D. M.
Published: June 2019

We report far-infrared observations of [0 I], [C II] and [O III] fine structure emission lines toward the nuclei of M82 and 7 other galaxies with a high rate of star formation. The far-infrared line emission is bright, contains about 0.5% of the bolometric luminosity in the central 60″, and is spatially concentrated toward the nuclei. In these galaxies between 10 and 30% of the interstellar gas near the nuclei is contained in a warm, atomic component. This atomic gas is probably located at the UV photodissociated surfaces of molecular clouds. The neutral gas in M82 has a temperature of ∼ 200 K, hydrogen density of ∼ 3 × 104 cm−3 and is very clumpy, indicating that the interstellar medium in this star burst galaxy is very different from that in the disk of our own galaxy. We discuss the implications of the infrared observations for the interpretation of mm molecular lines and for star formation at the nuclei of star burst galaxies.
CO Observations of the Nuclear Bar of IC 342
Authors: Hayashi Masahiko , Handa Toshihiro , Sofue Yoshiaki , Nakai Naomasa , Hasegawa Tetsuo , Lord Steven , Young Judith
Published: June 2019

We have mapped the nuclear region of an Scd galaxy IC 342 in the CO (J = 1-0) emission with an angular resolution of 15″. This galaxy has a bright optical nucleus with a dark lane elongated in the north-south direction. A prominent molecular bar which has been discovered by Lo et al. (1984) using the Owens Valley Interferometer lies just on the dark lane. Their CO map was spatially limited by the primary beam pattern and the velocity coverage of their spectrometer was not sufficient. It is not known, therefore, whether the molecular bar is connected to the outer spiral arms or not. We made the highest resolution CO map accessible by a single-dish telescope with a sufficient velocity coverage.
A Neutral Hydrogen Cloud in the Vicinity of the Elliptical Galaxy NGC 4318
Authors: Bottinelli L. , Fraix-Burnet D. , Gouguenheim L.
Published: June 2019

NGC 4318, in the Virgo Cluster, has the following optical properties:

—

morphological type: E (Nilson, 1973)

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BoT magnitude : 13.8 (Nilson, 1973)

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photometric axis : 0.8′ × 0.6′ (Nilson, 1973)

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heliocentric radial velocity:

−300 km s−1 (Arakelian et al., 1975)

1247± 15 km s (Tonry, 1981)

1215 km s−1 (Huchra et al., 1983)
MRK 273: A New OH Megamaser
Authors: Bottinelli L. , Fraix-Burnet D. , Gouguenheim L. , Kazès I. , Le Squeren A.M. , Patey I. , Rickard L. J. , Turner B. E.
Published: June 2019

Since the first detection of OH molecules in external galaxies, in 1971, hydroxyl observations have led to several detections of absorption lines in extragalactic systems. Though more seldom, OH maser emission has been observed in the 1667 and 1665 MHz main lines in NGC 253 and in the 1667 MHz line in M82. More recently, very powerful masers have been observed in IC 4553, NGC 3690 and Mrk 231.
Infrared Luminosities of Markarian Starburst Galaxies
Authors: Willner S. P. , Deutsch L. K.
Published: June 2019

Optical observations (Balzano 1983) have found many galaxies with unusually blue colors, stellar or semi-stellar nuclei, and emission line spectra with narrow line widths and line ratios implying stellar ionization. Balzano concluded that these properties could be explained by a recent burst of star formation; since almost all of the galaxies were selected from the Markarian lists, they are referred to as “Markarian starburst galaxies.” We have compared the far infrared luminosities of these galaxies with a sample of normal spiral galaxies (Scoville et al. 1983). We have also compared the far infrared luminosities of the Markarian starburst galaxies to their blue light and Hα luminosities.
U-G and G-R Colors of the Clumpy Irregular Galaxies Markarian 297 and 325
Authors: Tamura S. , Heidmann J.
Published: June 2019

U-G and G-R colors of clumps in Mrk 297 and Mrk 325 are presented. In addition, colors of other interesting objects and radiation sources were calculated for the Kiso UGR system. These objects are used to interpret the intrinsic characteristics of our sample. The observed colors of the clumps in both Mrk 297 and Mrk 325 are bluer than Im galaxies as well as main sequence stars and show scatter over the extent of the U-G vs. G-R diagram.
Photometric, Spectroscopic and 21-cm Line Investigation of Selected UV-Excess KISO and Clumpy Galaxies
Authors: Bottinelli L. , Gouguenheim L. , Hamabe M. , Heidmann J. , Maehara H. , Takase B.
Published: June 2019

A survey of Kiso UV-excess galaxies (KUGs) has been made using the 105-cm Kiso Schmidt telescope. We selected three galaxies of Ic-type (i.e. irregulars with clumpy HII regions). KUGs 1618+373, 1624+404 and 1626+413, and observed them together with a clumpy irregular galaxy Mrk 297 to clarify their star formation activity (Maehara et al. 1986).
CO Observations of the Spiral Galaxy IC 342
Authors: Wiklind T. , Rydbeck G. , Hjalmarson Å. , Rydbeck O.E.H.
Published: June 2019

We present observations of the Scd galaxy IC 342 in the J = 1-0 transition of CO, performed with the Onsala 20-m antenna. The spectra were obtained in a beamswitch mode.
Development of Millimeter Low-Noise Receivers at Nagoya University
Authors: Ogawa H. , Mizuno A. , Fukui Y. , Okuyama K.
Published: June 2019

We report the present status in the development of the millimeter-wave low noise receiver at Nagoya University.
Stellar Evolution and the Population Concept after 1950; The Vatican Conference
Authors: Blaauw A.
Published: June 2019

In the development of the concept of stellar populations the classification scheme adopted at the Vatican Conference of 1957 represents a major milestone. Thirteen years after Walter Baade's seminal papers, the conference reviewed progress in relevant fields of research and formulated a classification of population types that would remain the principal reference for the next decades. I shall review developments preceding the Conference, the initiatives that led to the Conference, the new scheme, and a few developments of later date.
Stars in the Galactic Halo
Authors: Kinman T.D.
Published: June 2019

The field star halo is comprised of those field stars that are like the stars found in the halo globular clusters. We discuss the halo properties — in particular whether Vrot is a function of z. An analysis of recent surveys for blue horizontal branch stars is described; the halo that is defined by these stars is composite and contains both a spherical and flat component.
Globular Cluster Systems in Other Galaxies
Authors: Harris William E.
Published: June 2019

A hypothesis or theory is clear, decisive, and positive, but it is believed by no one but the man who created it. Experimental findings, on the other hand, are messy, inexact things which are believed by everyone except the man who did that work.