bluuebunny/crossref_metadata_2025 huggingface dataset:
Proposed Very Long Baseline Interferometry at 103 MHz in India
Authors: Bhonsle R. V. , Alurkar S. K. , Degaonkar S. S. , Bobra A. D. , Sharma R.
Published: June 2019

Three radio telescopes operating at 103 MHz are being installed at Ahmedabad, Rajkot and Surat separated by about 200 km from each other for observing interplanetary scintillations (IPS) of compact radio sources for study of solar wind plasma dynamics as well as radio source size measurements for cosmological studies. Of these, two radio telescopes at Ahmedabad and Rajkot have been commissioned and started synchronous daily observations of IPS of a few compact radio sources with relative time accuracy of about ± 1 millisec. The third telescope at Surat is expected to go in operation by the end of 1983. As soon as all the three telescopes go in for simultaneous operation, it is proposed to (1) augment the telescope sensitivity so as to detect sources with flux density ~ 1 Jansky (2) incorporate better time and frequency standards at each station which can be synchronised to better than μs relative time accuracy (3) develop suitable receivers and data acquisition system for generating interference fringes using a general purpose computer and (4) take advantage of the availability of three telescopes to incorporate ‘closure phase and amplitude’ techniques which eliminate undesirable atmospheric and ionospheric phase distortions.
Positional Astronomy and Stellar Masses
Authors: Heintz W. D.
Published: June 2019

In this paper are surveyed the combinations of data needed for mass determinations, the impact of radial-velocity and speckle observations, the 1983 catalog of visual-binary orbits, the current material for main-sequence and red-dwarf masses and the controversial methods and results on low mass objects.
Measuring Stars with High Angular Resolution: Results from Narrabri Observatory
Authors: Hanbury Brown R.
Published: June 2019

The stellar intensity interferometer at Narrabri Observatory was used to measure the angular diameters of 32 stars in the spectral range 05f to F8 and brighter than about V = +2.6. The results were combined with measurements of absolute flux and, in a few cases parallax, to find the emergent flux, effective temperature, radius and luminosity of the stars. The methods used to calibrate these measurements and their uncertainties are discussed. It is shown that in measuring emergent flux and effective temperature the major uncertainties were most frequently in the measurements of angular size.
Calibration in Temperature of Photometric Parameters
Authors: Hauck B.
Published: June 2019

It is very easy to use a Planck distribution to show that a color index is a temperature parameter, but it is more difficult to calibrate such a color index in terms of temperature because only a few Teff values are determined. A pioneering work is that of Kuiper (1938), who derived a temperature scale according to spectral type (from A0 to M2 for dwarfs and from G0 to M8 for giants) and a Becker index. The first study giving a relation between Teff and a photoelectric color index is that of Popper (1959) in which the author derives a relation between Teff and B-V for the A and F stars and for G8 to K5 (dwarf and giant) stars. On this occasion, Popper shows the relation between temperature parameters of two photometric systems, R-I from the six-color system of Stebbins and Whitford, and B-V. This work was followed by a quantity of others from numerous authors in various systems, one of the most important being that of Johnson (1966). The purpose of the present study is not to review all the relations to be found in the literature but to define a set of stars which can be used to determine a calibration of a photometric parameter in terms of Teff.
An Empirical Hγ - Luminosity Calibration
Authors: Millward Christopher G. , Walker Gordon A. H.
Published: June 2019

High signal-to-noise Reticon spectra for 87 members of 8 open clusters and associations together with 37 stars having reliable parallaxes (early A-type stars with reliable trigonometric parallaxes, eclipsing binaries, and visual binaries) have been used to calibrate the W(Hγ)-Mv relation for spectral types 0 to early A of luminosity classes III-V. The new calibration has a mean probable dispersion of ±0.28 mag. The distance modulus of the Pleiades is 5.54 ± 0.06 mag, which is in excellent agreement with other, recent determinations, as are the distance moduli for all the calibrating clusters. The use of visual-binary parallaxes implies a Hyades distance modulus of about 3.0 which is significantly smaller than the Hanson (1980) value of 3.30 mag. Although no spectral-type corrections are necessary, stellar evolution probably affects the construction of the new calibration and special care should be taken when determining distance moduli from slightly evolved cluster sequences or for individual stars. Systematic departures from the calibration may be present for stars with Vsin i ≥ 220–250 km/sec. Significant residuals are found between our values of W(Hγ) and those of Petrie in the range 1–13 Å equivalent width, which are due in part to systematic errors in Petrie's W(Hγ) measures. Our distance modulus of 11.11 mag for NGC 2244 is in excellent agreement with the photometric distance. The new calibration is compared to other early type star calibrations for main sequence stars. It is 1.2 mag brighter than Petrie's (1965) Hγ calibration at spectral type 06 and 0.7 mag brighter at A3. For types B1 and earlier the new calibration averages 0.4 mag brighter than the Balona and Crampton (1974) Hγ calibration. There is generally good agreement with the Blaauw (1963) MK calibration although the latter is 0.4 mag brighter at spectral type BO. The Crawford (1978) Hβ calibration is up to 0.5 mag brighter for the earlier spectral types and 0.4 mag fainter for later types. More complete discussions of the Hγ-luminosity calibration are available in Millward and Walker (1984, 1985).
Problems Concerning Planck's Blackbody Law
Authors: Galgani Luigi
Published: June 2019

For the calibration of radiation detectors, use is currently made of blackbodies, assuming they satisfy Planck's Law. The first problem considered here is then: how well has this law been checked experimentally? Now, it has been pointed out (Crovini and Galgani 1984) that essentially no new experiments have been made after 1921 (Rubens and Michel 1921), when the data were interpreted as fitting the theoretical law within 1%. But, in fact, this work made use of the value 14300 (in suitable units) of the second radiation constant, while the presently adopted value is 14388. When one inserts this value into the calculations, one finds that, indeed, Planck's Law has been checked only to 3%.
Effective Temperatures of Stars with “Standard” Angular Diameters
Authors: Glushneva I. N.
Published: June 2019

For 12 stars from the list of stars with “standard” angular diameters (Fracassini et al. 1983), effective temperatures, bolometric corrections, radii and luminosities were determined. These stars are included in the stellar spectrophotometric catalog of the Sternberg Astronomical Institute and three of them were used as spectrophotometric standards. A comparison was made of Teff obtained directly using angular diameters from the list of Fracassini et al. (1983) and by means of joint determination of Teff and θ (Blackwell and Shallis 1977). For 7 stars the differences in Teff values don't exceed 1–1.5% and the maximum discrepancies are about 6% for BS 2294, 2943 and 4% for the spectrophotometric standard α Aql (BS 7557). Effective temperature values of α Lyr obtained by these two methods are in the agreement within 0.5%.
High-Precision Solar Radiation Data for λλ3300–12500Å
Authors: Neckel Heinz , Labs Dietrich
Published: June 2019

Very precise data on the solar radiation has been obtained by merging: (1) the absolute integrals of the disk-center intensity for 20Å-wide spectral bands, observed in the 1960's by Labs and Neckel (1962, 1963, 1967); (2) the ratios of the mean-to-central intensity following from observations of the center-to-limb variation of (a) all 20Å bands below 6600Å (Neckel and Labs 1984), and (b) the intensities at selected continuum wavelengths (Pierce and Slaughter 1977a, b); and (3) the high-resolution Fourier transform spectra (FTS) obtained by J. Brault at Kitt Peak for the center of the disk and for the irradiance.
Secondary Standard Stars in the Four-Color System
Authors: Philip A. G. Davis
Published: June 2019

Now that larger telescopes are being used to make photometric measures of very faint stars, fainter standard stars are needed. Most of the stars listed in the standard star list of Crawford and Barnes (1970) are too bright, even for a 1.5 m telescope. Over the past two decades observations have been made of B, A and F-type stars in the magnitude range V = 6 to 13 in the northern and southern hemispheres in a program of four-color photometry of field and blue horizontal-branch stars. An earlier list of secondary standards was published in Philip and Philip (1973). The present paper reports on over twice as many standard stars and the secondary standards are increased by about 20%. The number of observations per star is substantially increased.
On Photometric Standards and Color Transformation
Authors: Manfroid J.
Published: June 2019

We have carried out a preliminary investigation of a method of observation and reduction which leads to a large improvement in the accuracy of the color transformation of photometric measurements. This method involves the use of extra filters for some of the observations. It is argued that the better precision obtained is well worth the additional telescope work.
Calibration of Photometric Systems from Homogeneous Spectrophotometric Data
Authors: Labhardt Lukas , Buser Roland
Published: June 2019

The atlas of stellar spectrophotometric data published by Gunn and Stryker (GS, 1983) constitutes an extremely valuable tool for the evaluation and calibration of photometric systems. The resolution of the scanner fluxes (10 or 20 Å), given for a broad wavelength range (λλ 3160–10620 Å) and the systematic coverage of stellar types are (almost) ideal for calculating synthetic colors for Becker's (1946) photographic RGU system which has been extensively applied in galactic structure work (cf. Buser 1981). Since RGU photometry is tightly linked to UBV data (Steinlin 1968, Buser 1978b), the Gunn-Stryker atlas has been used in the present paper to evaluate these two systems and subsequently investigate the resulting calibration of the RGU colors in terms of MK spectral classification.
The Effect of Metallicity and Pulsation on the Infrared Colors of Luminous M Giants
Authors: Bessell M. S. , Brett J. , Scholz M. , Wood P. R.
Published: June 2019

The temperature calibration for cool stars and in particular the Miras continues to be contentious. Lunar occultations have provided radii for many K and M stars and a good temperature calibration has been derived for the hotter non-variable M stars (Ridgway et al. 1980). The situation for the Miras and carbon stars and the metal-rich and metal-poor M stars is, however, not so clear cut. Observations are generally made in some broad-band color such as (R-I), (V-K) or (J-K) and a temperature derived using either the Ridgway et al. (1980) empirical scale or a black-body scale; differences can amount to several hundred degrees. We decided to theoretically explore the effects that extension, metallicity and pulsation could have on colors.
The Temperature Scale of G and K Subgiants
Authors: Frisk U. O. , Bell R. A.
Published: June 2019

This investigation of nearby Population I stars was motivated by our need for accurate effective temperatures in order to be able to obtain reliable N abundances from lines belonging to the CN red system. These determinations are based on narrowband photometry calibrated by means of synthetic spectra. It is believed that the temperatures are accurate to within 100 K. The results show that recent calculations of evolutionary tracks of G and K subgiants predict the observations quite well. However, a value for the mixing length parameter 1/Hp close to 1.6 is required.
MV and Teff of B-Type Stars as Derived from 13-Color Photometry
Authors: Conconi P. , Mantegazza L.
Published: June 2019

The 13 color medium-narrow band photometric system (Johnson and Mitchell 1975) potentially contains a great deal of information, but so far only a little work has been done in order to recover some physical parmeters from its color indices. Our aim is to obtain relations to be used in calibrating this system in terms of physical quantities, making use of the information given by this system alone.
The Temperatures of G and K Stars
Authors: Wing Robert F. , Gustafsson Bengt , Eriksson Kjell
Published: June 2019

Effective temperatures have been determined for G and K stars by comparing synthetic colors computed from model atmospheres to observed colors measured at near-infrared continuum points. Results are presented for giant stars in the range K0 III - K4 III.
Standard Pulsars: Probes for the Calibration of the Galactic Continuum Background Temperature and the Electron Density of the Interstellar Medium
Authors: Fracassini M. , Pasinetti L. E.
Published: June 2019

From the list of observed and derived parameters of 330 pulsars published by Manchester and Taylor (1981), we have selected sixteen “standard” pulsars whose position and radio luminosity fit well a statistical relation found by Antonello and Fracassini (1984). This relation shows also that these pulsars may be considered as probes of the galactic places where the observed 408 MHz continuum background temperature, T408, and the computed electron densities, ne, of the interstellar medium, ISM, are best correlated.
Ionized Disk/Halo Gas: Insight from Optical Emission Lines and Pulsar Dispersion Measures
Authors: Reynolds R. J.
Published: June 2019

Warm (≈ 104 K), diffuse H+ is a significant component of the interstellar medium within the Galactic disk and lower halo. This gas accounts for about one quarter of the interstellar atomic hydrogen, consumes a large fraction of the interstellar power budget, and appears to be the dominant state of interstellar matter 1 kpc above the midplane. The origin of this ionized gas is not yet established; however, of the known sources of ionization only 0 stars and perhaps supernovae produce enough power to balance the “cooling” rate of the gas. If 0 stars are the source of the ionization, then the interstellar HI, including the extended “Lockman layer”, must have a morphology that allows about 14% of the Lyman continuum photons emitted by the stars to travel hundreds of parsecs within the Galactic disk and up into the lower halo.
Molecular Clouds and Star Formation at Large R
Authors: Brand J. , Wouterloot J.G.A.
Published: June 2019

In the outer Galaxy (defined here as those parts of our system with galactocentric radii R>R0) the HI gas density (Wouterloot et al., 1990), the cosmic ray flux (Bloemen et al, 1984) and the metallicity (Shaver et al., 1983) are lower than in the inner parts. Also, the effect of a spiral density wave is much reduced in the outer parts of the Galaxy due to corotation. This changing environment might be expected to have its influence on the formation of molecular clouds and on star formation within them. In fact, some differences with respect to the inner Galaxy have been found: the ratio of HI to H2 surface density is increasing from about 5 near the Sun to about 100 at R≈20kpc (Wouterloot et al., 1990). Because of the “flaring” of the gaseous disk, the scale height of both the atomic and the molecular gas increases by about a factor of 3 between R0 and 2R0 (Wouterloot et al., 1990), so the mean volume density of both constituents decreases even more rapidly than their surface densities. The size of HII regions decreases significantly with increasing galactocentric distance (Fich and Blitz, 1984), probably due to the fact that outer Galaxy clouds are less massive (see section 3.3), and therefore form fewer O-type stars than their inner Galaxy counter parts. There are indications that the cloud kinetic temperature is lower by a few degrees (Mead and Kutner, 1988), although it is not clear to what extent this is caused by beam dilution.
Radio Studies of Cosmic Rays in the Galaxy
Authors: Reich W.
Published: June 2019

Changes of the cosmic ray electron spectrum throughout the Galaxy have been found, based on the comparison of large-scale radio continuum surveys. These observations are not compatible with the assumption of a static Galactic halo, but indicate the existence of a Galactic wind. Galactic plane surveys reveal sources of cosmic ray electrons in the Galactic disk. Recent studies of the population of radio sources show no evidence for a large number of compact Galactic non-thermal sources. Most of the extended sources are probably HII-regions. Relatively few new supernova remnants (SNRs) with low surface brightness could be identified. Most of the non-thermal emission in the disk-halo interface seems diffuse or unresolved, even at arcmin angular resolution.
Magnetic Fields in Disks and Halos of Spiral Galaxies
Authors: Beck Rainer
Published: June 2019

Spiral galaxies host interstellar magnetic fields of 4-15 μG total strength. A significant fraction of the field lines shows large-scale structures. At face-on or moderately inclined view, the field lines run generally parallel to the spiral arms, either with uniform direction with respect to azimuthal angle (axisymmetric spiral, ASS), with one reversal along azimuthal angle (bisymmetric spiral, BSS), or with spiral orientation without dominating direction.

At edge-on view, the field is concentrated in a thin disk, often surrounded by a thick radio disk with field lines mostly parallel to the plane, similar to the quadrupole-type dynamo field. Radio polarization data from NGC891 indicate that the thermal gas seen in Hα is responsible for Faraday depolarization. The required scaleheight of the field of ~4 kpc is comparable to the value expected in case of energy equipartition between magnetic fields and cosmic rays. The interacting edge-on galaxy NGC 4631 shows a much larger radio halo with field lines perpendicular to the disk, possibly driven by a strong galactic wind or the result of a dipole-type halo field.

Field lines bending out of the plane are also visible in face-on galaxies as regions with high rotation measures and low star-formation activity. The resemblance to the phenomenon of the solar corona suggests to call them “galactic coronal holes”.
Particle Acceleration in the Disk-Halo System
Authors: Schlickeiser Reinhard
Published: June 2019

The recent observations of the nonthermal properties of the halo of our Galaxy at radio and γ-ray wavelengths are summarized. Radio and γ-ray data show a similar spectral flattening with Galactic height towards the anticenter direction, which is interpreted as a cosmic-ray effect. Several theoretical explanations for the flattening of the energy spectra of the radiating cosmic-ray electrons (in the radio) and nucleons (in γ-rays) are reviewed including propagation of cosmic rays in an accelerating Galactic wind and the presence of cosmic-ray sources with flat energy spectra in the halo.
Splitting of Periodic Comets
Authors: Forti Giuseppe
Published: June 2019

Among the comets that were observed to break in two or more fragments, only a few of them are periodic. So far the dynamic study of the relative motion of a secondary nucleus with respect to the primary has supposed that a cometary fragment is subject to a small and continuousradialnongravitational force after separation at rest. This force acts against the solar attraction and varies according to an inverse square law. A small impulse at break up may also be invoked in some case. A different approach is followed in this paper when dealing with a fragment of a periodic comet: after separation the motion of a secondary nucleus is characterized by nongravitational forces which vary according to the sameg(r) law currently used for the primary.

Results of the study of comets P/Biela and P/du Toit-Hartley show that the motion of their fragments after separation is characterized by nongravitational parameters which are larger than those of the parent bodies. Both fragments lasted for about 2 full revolutions and three returns.
Planetary Nebulae with Massive Nuclei
Authors: Tylenda R.
Published: June 2019

Massive central stars (M > 1 Mo) of planetary nebulae burn nuclear fuel on a time scale of hundreds or tens of years which is shorter than the recombination time in a typical planetary nebula. Consequently the ionization and thermal structure of a nebula with such a nucleus is expected to be far from equilibrium conditions. The greatest chance of observing such a nebula is when the central star cools down to the white dwarf region. Time-dependent photoionization models suggest the following non-equilibrium effects to be expected at this stage. Firstly, the nebula shows a double shell structure, i.e. a bright, inner ring is surrounded by a faint, extended halo best seen in the HI lines and infrared lines from low-ionization species, such as (Ne II) 12.8 μ. Secondly, the low-excitation emission ((O II), (Ne II), (S III)) is enhanced relative to the high-excitation ((O III), (Ne III), (S III)). Thirdly, different modifications of the Zanstra method result in significantly different temperatures for the central star with a general rule that THI > THeII > THeII/HI The He II Zanstra method gives the most reliable result. Fourthly, the electron temperature derived from the (O III) lines is appreciably higher than that obtained from the (N II) lines. It is suggested that NGC 7027 and NGC 2440 possess massive central stars and that the above time-dependent effects are currently observed in these nebulae.
Final Review
Authors: Terzian Yervant
Published: June 2019

What splendid laboratories have planetary nebulae been! We have heard of important observations in the ultraviolet, optical, infrared, and radio spectral ranges, all rich in astrophysical information. We are now certain that planetary nebulae represent a crucial phase of stellar evolution. We have also begun to study the fine details of the evolution of planetary nebulae and our endless aim is to understand these objects completely.
High-Spatial Resolution Observations of Planetary Nebulae
Authors: Hua C. T. , Louise R.
Published: June 2019

Monochromatic images in Hα, Hβ, (NII) λ 6584, (SII) λ 6717 and (OIII) λ 5007 lines are presented for morphological study of planetary nebulae. Narrow bandpass (Δλ = 5 to 10 Å) interference filters are generally used in order to discriminate peculiar structures existing in different emission lines. However, large bandwidths (Δλ = 50 Å) along with long exposures, are also necessary in searching for faint nebulosities associated with planetaries.
Physical Conditions in the Planetary Nebula Hb 12
Authors: Flower D.R. , Penn C.J.
Published: June 2019

The planetary nebula Hb 12 has recently been observed at infrared (Aitken et al., 1979) and radio (Purton et al., 1982) wavelengths. The detection of a silicate emission feature in the 8-13 μm region suggests that the nebula is oxygen rich. A high emission measure is derived from the radio spectrum, implying a high intrinsic density.
Ultra-Violet Spectrophotometry of Some Hotter Central Stars
Authors: Clegg R.E.S. , Seaton M.J.
Published: June 2019

A spectrophotometric survey has been made for about 20 central stars of planetary nebulae, with emphasis mainly on hot stars. We use low-resolution IUE spectra, observed by ourselves or obtained from Data Center, together with, in some cases, results from optical observations. Data have been extracted and merged, regions of saturation eliminated, ITF errors corrected and nebular continua subtracted. Careful assessments have been made of reddening constants, and of data used to calculate Zanstra temperatures.
Extinction - Distances to Planetary Nebulae
Authors: Gathier R. , Pottasch S.R.
Published: June 2019

Individual distances to planetary nebulae (PN) which are independent of any assumption of average nebular characteristics, can be found if one knows the relation between interstellar extinction (E(B-V)) and distance along the line-of-sight to the PN, together with the E(B-V) towards the PN itself (Lutz, 1973 and Acker, 1978). We used VBLUW-photometry (Lub and Pel, 1977) to derive accurate E(B-V)'s and distances of stars up to V-magnitude + 14, within 0°.3 from the PN. Table 1 lists the PN we studied. The E(B-V)'s of the PN are derived from:
Discovery of a Large High-Excitation Planetary Nebula
Authors: Heckathorn J. N. , Fesen R.A. , Gull T.R.
Published: June 2019

The discovery of a new planetary nebula from (O III) interference filter imagery is reported. The nebula, PN 136 + 5°1, is 15′ in diameter and asymmetric in appearance. Spectrophotometry of the central regions indicate it is of excitation class between 8 and 10. A single bright condensation within the nebula exhibits emission lines of much lower ionization with (S II) λλ 6717, 6731 line intensities indicating an electron density of about 350 ± 150 cm−3. Seeing limited (O III) imagery of this planetary nebula is also presented. (This article is appearing in Astron. Astrophys. in the near future).
Evidence of Collective Formation of Low Mass Stars in the Dark Cloud Kh141
Authors: Tomita Yoshio , Ohtani Hiroshi
Published: June 2019

To find evidence for collective star formation without massive stars in the dark cloud complex Kh141 (Saito 1980), a search for T-Tauri stars has been made.
T-Tauri Stars in Taurus: Infrared Analysis of the IRAS Sample
Authors: Harris Stella , Hughes Joanne
Published: June 2019

This paper describes further development of the study of a set of IRAS-defined T Tauri stars, located within the Taurus region (taken as the area RA = 4h to 5h; dec = +16° to +31°), and selected from the IRAS point-source catalogue purely on the basis of their [25 m – 12 m] and [60 m – 25 m] colours. The original selection, which is described elsewhere (Harris, 1985) was based on an analysis of the IRAS colours of the known T Tauri stars within the region (found to be tightly defined, and representing blackbody temperatures between about 200 and 300 K, and 100 and 200 K, respectively), and gave the intriguing result that the extended sample, defined purely by these colours, adhered strongly to the geographic clustering found previously both for the known T Tauri stars and for the (presumably very much younger) ‘dense core sources’.
CO, 13CO, and HCN(J = 1-0) Observations of L1204(S140)
Authors: Sugitani K. , Fukui Y.
Published: June 2019

We present results of CO, 13CO, and HCN(J = 1-0) observations of L1204 by the 4 m telescope of Nagoya University.
12C18O in OMC-1: Kinematics, Molecular Column Density, and Kinetic Temperature Distribution
Authors: Wilson T. L. , Serabyn E. , Henkel C. , Walmsley C. M.
Published: June 2019

A fully sampled map of size ∼1′×3′ (R.A. Dec), centered on BN-KL has been made in the J = 1-0 line of 12C18O with 21″ angular resolution. The 12C18O emission is concentrated in a ← 40″ wide continuous strip running S to NE. Several maxima are superposed on the ridge, but none exceeds the average emission level by more than 40%. There is no intense peak of 12C18O J = 1-0 line emission centered on BN-KL, in contrast to maps of the dust emission. The dust and 12C18O results can be reconciled with a constant (CO/H2) ratio if there are variations in the kinetic temperature and column density of ∼50%. Peaks in both temperature and column density are then located near BN-KL, and 90″ to the south. From the estimated CO column density, about 10% of the carbon is in the form of CO. Near the BN-KL region, the 12C18O line profiles tend to become wider. These wider lines appear to be superposed on a weak, 18 km s−1 (FWHP) wide pedestal. In regions 40″ NE and 30″ S of BN-KL, the 12C18O lines have widths of less than 2 km s−1. Presumably, these are the locations of high density, quiescent molecular gas. The radial velocity of the CO emission increases from 6.5 km s−1 (at 90″ S) to 10.5 km s−1 (at 60″ NE) of BN-KL. Close to BN-KL, however, there is evidence that this trend is reversed.
Two Dimensional Models for the Orion Nebula and M17
Authors: Rubin R. H. , Simpson J. P. , Erickson E. F. , Haas M. R.
Published: June 2019

We apply a 2-D, axisymmetric code for modeling H II regions (Rubin Ap. J. 287, 653, 1984) to observations of the Orion Nebula. The model solves for the ionization and thermal structure and radiative transfer for the quasi-equilibrium volume. Assuming that the Orion Nebula is viewed face-on (along the symmetry axis) and that the geometry/density distribution is plane parallel with an exponential density gradient perpendicular to the slab, we use a x2 minimization technique to best fit the radio continuum maps. The best fit to the Schraml and Mezger map (Astrophys. J. 156, 269, 1969) has a density at the star of ∼1800 cm−3, a scale height of ∼0.23 pc, and ∼1.5x1049 ionizing photons s−1 so that ∼ 1/3 of the ionizing photons from the exciting source are escaping the nebula through the frontal density-bounded direction. Our model for Orion requires circular symmetry in the plane of the sky; nonsymmetrical features such as the ionization bar toward the SE cannot be reproduced. Further modeling that compares with line observations has been delayed to incorporate the important role played by recombinations in populating low-lying [O II] levels (Rubin 1985, Astrophys. J., submitted).
Clumpy Structure in the W3 Molecular Core
Authors: Kobayashi Hideyuki , Hayashi Masahiko , Hasegawa Tetsuo
Published: June 2019

The core region of the W3 molecular cloud has high molecular line luminosities (Dickel et al. 1980; Brackman and Scoville 1980). This region contains luminous infrared sources and ultra compact H II regions. A young star cluster may be forming in this region. Recent interferometric high angular-resolution observation revealed a bipolar outflow toward IRS 5 in the CO emission (Claussen et al. 1984) and a mass condensation in the HCN emission (Wright et al. 1984) in this region.
Shocked Molecular Hydrogen from Star Forming Regions
Authors: Lane Adair P. , Bally John
Published: June 2019

Near infrared (2 micron) emission lines from molecular hydrogen provide a powerful probe of the morphology and energetics of outflows associated with stellar birth. The H2 emission regions trace the location of shock waves formed when the high velocity outflow from young stars encounters dense quiescent gas. Since H2 is the dominant coolant of the hot post-shock molecular gas, the H2 lines provide a measure of the fraction of the total mechanical luminosity radiated away from the cloud.
The Formation of Planets Around Stars of Various Masses and the Origin and the Evolution of Circumstellar Dust Clouds
Authors: Nakano Takenori
Published: June 2019

The formation of planets is investigated both in a gaseous nebula and after the nebula has been blown away. The capture of planetesimals by a protoplanet is investigated by taking into account the growth of planetesimals. The time of planet formation is determined as a function of distance from the central star. The formation time of Neptune is found to be 3.9 × 109 yr, value shorter than the age of the solar system. The region where planets form within the stellar lifetime is determined, and it is found that only stars of mass less than several solar masses can have planets. The dust clouds around α Lyrae and β Pictoris are far outside the planet-forming regions. A model for the circumstellar dust cloud is proposed which can explain the basic properties of the β Pic disk.
High Velocity OH in Bipolar Flows
Authors: Mirabel I. F.
Published: June 2019

High velocity OH was detected in absorption in several star forming regions. The supersonic OH shows similar bipolar geometry as the CO. The absorbing OH appears to trace the part of the outflows with the highest velocities and lower densities, and provides information on the structure of the outflows at large distances from the central source. At scales of 0.1 to 0.5 parsecs the outflows are elongated in the direction of the steepest density gradient in the ambient cloud. The transitions in the supersonic OH are markedly subthermal (Tex < 3.8 K), since the radiation that is being absorbed is the cosmic background plus a small galactic contribution. We propose a cooling mechanism for the OH analogous to the adiabatic magnetic cooling of paramagnetic salts used in low temperature physics. Magnetic cooling is a potentially important mechanism for astrophysics.
Star Formation and Bipolar Flows
Authors: Pudritz Ralph E.
Published: June 2019

Observations of molecular outflows from regions of star formation show that they cannot be radiatively driven ((Ṁv)mol ≥ 102 – 103 (L./c)). The thrust observed to be associated with the smaller scale ionized outflows is also incapable of driving the molecular gas ((Ṁv)ion ≃ (L./c), Persson et al 1984). The results may be explained if bipolar flows are hydromagnetic winds from molecular disks around protostars. These winds carry off disk rotational energy (observed as the mechanical energy of the outflows) and angular momentum (observed when rotation of the outflowing gas is found), which drives an accretion flow through it and onto the protostellar core (Pudritz 1985, Pudritz and Norman 1983, 1986). Therefore star formation and bipolar outflows occur simultaneously when magnetized, rotating disks are the source of activity.
Hα and [S II] Direct Images of Herbig-Haro Objects 1 and 2 with the Mepsicron Detector
Authors: Echevarría J. , Bohigas J. , Torrelles J. , Cantó J.
Published: June 2019

Using the Mepsicron detection system, we obtained images of the region around Herbig-Haro objects 1 and 2. These images were taken with interference filters centred on Hα, on the red continuum (6648 A) and on the [S II] line at 6731 A.
The Structure of the HH39 Region
Authors: Walsh J. R.
Published: June 2019

HH39 is the group of Herbig-Haro (HH) objects associated with the young semi-stellar object R Monocerotis (R Mon) and the variable reflection nebula NGC 2261. An R CCD frame and a B prime focus plate of the region show a filament connecting NGC 2261 with HH39, confirming the association between R Mon and the HH objects. This filament is probably composed of emission material. The southern knot in HH39 has brightened over the last 20 years; its proper motion has been determined and is similar to that of the other knots. A total of 8 knots can be distinguished in HH39 surrounded by diffuse nebulosity. High resolution spectroscopy of the Hα and [N II] emission lines shows the spatial variation of the radial velocity structure over the largest knots (HH39 A and C). Distinct differences in excitation and velocity structure between the knots are apparent. The observations are compatible with the knots being high velocity ejecta from R Mon, decelerated by interaction with ambient material and with bow shocks on their front surfaces.
Models for the Emission-Line Spectra of the Low-Excitation Herbig-Haro Objects
Authors: Dopita Michael A. , Caganoff Saul , Schwartz Richard D. , Cohen Martin
Published: June 2019

The class of Low-Excitation Herbig-Haro Objects are characterised by [SII] and [OI] lines which are comparable in strength to H-Alpha, by [NI] lines that are comparable to H-Beta, relatively weak [NII] and [OII] lines, little or no [OIII] emission and a very strong blue-UV “excess”. This blue and UV continuum in low-excitation HH Objects was noted as a problem by Brugel, Böhm and Mannery (1981), Ortalani and D'Odorico (1980) and Böhm, Böhm-Vitense and Brugel (1981). The first suggestion that it results from collisionally enhanced Hydrogen two-photon (2q) continuum was by Dopita (1981). The subsequent observations of Dopita, Binette and Schwartz (1982) proved that this was indeed the case. However, although very close correlations between this enhancement and the emission-line spectrum were found, a fair theoretical description could only be obtained for very youthful shock models with ages of order 30 years. However, there seems to be no reason why low excitation HH shocks should be much younger than the high excitation shocks.
Hydrogen Cyanide in the Bipolar Source CEP A
Authors: Weliachew L. , Emerson D. T. , Forveille T. , Bieging J. H. , Wright M.C.H. , Ellder J.
Published: June 2019

The Cep A molecular cloud has been mapped in the 87 GHz continuum and in the J = 1-0 transition of HCN with a combination of single antenna and interferometer observations. The resolution is 19″x14″ (about 0.06 pc at the distance of Cep A) and 0.8 km/sec in velocity.
The Molecular Observations of the Central Part of the S106 Molecular Cloud
Authors: Kaifu Norio , Hayashi Saeko S.
Published: June 2019

S106 is an optical bipolar nebula which is elongated in the north-south direction. In the center, there is an infrared source and an ultra-compact H II region, indicating that a young, massive star has been just formed. A high resolution VLA map by Bally et al. (1983) and Felli et al. (1984) revealed a well confined bipolar-shaped H II region with a dust layer in its center. The dust layer which is inclined 25° from the east-west direction is extremely interesting because it seems to indicate that the cold molecular disk is very thin in the central part. A massive molecular core elongated in the east-west direction was observed with CO emission by Bally and Scoville (1982). In the central part, Bieging (1984) reported the detection of a rotating compact disk with HCN emission using the Hat Creek mm-array, which might be a molecular counterpart of the dust layer observed by Bally et al. (1983) and Felli et al. (1984).
Equilibrium and Collapse of Rotating Isothermal Clouds
Authors: Narita S. , Kiguchi M. , Miyama S. M. , Hayashi C.
Published: June 2019

We have performed numerical calculations for both static and dynamic structures of molecular clouds in which stars would be formed. The assumption in our calculations is that a cloud, which is embedded in an external hot and tenuous uniform medium, is isothermal and axisymmetric.
A Helical Magnetic Field Model of the Jets
Authors: Maruyama T. , Fujimoto M.
Published: June 2019

A hydromagnetic model is presented for the bipolar flow of molecular gas from newborn stars and for the radio jet emerging out of active galactic nuclei. We assume a tightly-twisted helical magnetic field in the jet, which can collimate and accelerate the gas along the jet axis. The Lorentz force is also shown to rotate the gas around it.
Equilibria and Dynamics of Isothermal Clouds
Authors: Hayashi Chushiro
Published: June 2019

First, equilibrium structure and maximum mass of a rotating isothermal cloud are described. Second, growth rate of fragmentation instability in an infinite disk and filament is presented. Finally, results of 2D and 3D simulations of collapse and fragmentation of rotating isothermal clouds are reviewed and comments are given.
Gravitational Instability of Rotating Gaseous Disks with Magnetic Fields
Authors: Nakamura Takashi , Iwata Takuji
Published: June 2019

The gravitational instabilities are investigated for rigidly rotating isothermal gaseous disks with a magnetic field whose mean direction is parallel (case A) and perpendicular (case B) to the rotation axis. The linearized equation for the perturbation becomes an eigen value problem which is solved numerically. The stability depends on two non-dimensional parameters p2 ≡ B20/(4π2Gσ20) and q2 ≡ Ω20/(π Gρ0c) where B0, σ0, Ω0 and ρ0c are the magnetic field strength, the column density of the disk, the uniform angular velocity and the central density, respectively.
3D Simulation of Interstellar Cloud Collision and Triggered Star Formation
Authors: Nagasawa Mikio , Miyama Shoken M.
Published: June 2019

Cloud-cloud collision has been regarded as one of the important mechanisms which triggers star formation. But a detailed analysis on the change of the critical mass has been absent due to the poor resolution of numerical experiments or limited by the assumption of a geometrical symmetry. We simulate the collisions between isothermal interstellar clouds using a three-dimensional hydrodynamic code (Smoothed Particle Method). The simulation in three dimensions gives us not only the criterion for the trigger of star formation but also the information about the origin of the interstellar cloud rotation and its initial distribution of angular momentum.
Fragmentation of Isothermal Sheet-Like Clouds
Authors: Miyama Shoken M. , Narita Shinji , Hayashi Chushiro
Published: June 2019

Growth of perturbations and fragmentation of isothermal sheet-like clouds are computed three dimensionally. An initial cloud is a self-gravitating equilibrium gas layer with small fluctuations, which have the form ei(kxk+kyy). The simulations of models with various values of kx and ky are performed.
The Bell Laboratories CO Survey: Star Formation in Spiral Arms
Authors: Stark A. A. , Bally J. , Knapp G. R. , Krahnert A. , Penzias A. A. , Wilson R. W.
Published: June 2019

We present a galactic survey which to date consists of 47,000 positions covering −3° < l < 122°, −1° < b < 1°, observed in the J= 1→ 0 line of 13CO to an rms noise level of 0.15 K in 0.68 km s−1 channels, using the 7 m antenna at Crawford Hill. Maps made from the survey data show a clear difference between spiral arm and interarm regions. The signature of spiral structure on kiloparsec scales is the presence in galactic survey data of voids in l, b, v space which contain many times fewer Giant Molecular Clouds (GMCs) than do adjacent regions of similar size. The difference between arm and interarm regions in the inner galaxy is manifested only in the GMCs — small clouds are present throughout. These results are based on catalogs of clouds and their estimated sizes in 13CO. We suggest that GMCs are formed as interstellar gas enters a spiral arm, and that they break up into small molecular or atomic clouds as the gas leaves the arm.
Star Formation in Normal Irregular Galaxies
Authors: Hunter Deidre A.
Published: June 2019

Normal, non-interacting irregular galaxies can be quite successful at forming stars. Therefore, spiral density waves are not necessary to a vigorous production of stars. Nevertheless, there is a large range in star-formation rates among irregular galaxies. Irregulars with common characteristics can have different overall levels of star-formation activity, so that the level of activity does not seem to be simple related to observable global properties of galaxian systems. The constant star formation rates of most normal irregulars also imply the existence of regulatory processes.
NGC 2363, A Giant Extragalactic H II Region
Authors: Peimbert M. , Peña M. , Torres-Peimbert S.
Published: June 2019

NGC 2363 is one of the extragalactic HII regions with the highest surface brightness in Hα and in λ5007. We discuss the physical conditions within this star-forming region. In particular, from spectrophometric studies in the 1200-7400 A range we have determined its chemical abundance. We find that the O/H is an order of magnitude smaller than in the solar vicinity, and that the C/O ratio is a factor of two smaller.
Star Formation in Nuclei of Early-Type Galaxies
Authors: Rocca-Volmerange B. , Guiderdoni B.
Published: June 2019

A far-UV population synthesis is performed with the IUE Spectral Atlas on absolute spectrophotometry for nuclei of early-type galaxies. Two types of stellar populations may be distinguished in gas-poor galaxies: a) the bulk of evolved stars mostly contributing in the 2000 A – 3000 A wavelength range as well as in the visible. The Long Wavelength Range IUE spectra appear to be excellent indicators of the turn off age in galaxy nuclei; b) a possible young massive star population which could be the origin of the far UV excess in most cases and which is essentially contributing in the 1200 A – 2000 A wavelength range. Spectral features of massive stars may be identified.
High-Dispersion Spectroscopy of the Clumpy Irregular Galaxies Markarian 297 and 325
Authors: Taniguchi Y. , Tamura S.
Published: June 2019

High-dispersion spectroscopic observations with good spectral resolution have been made of the four clumps in the two clumpy irregular galaxies Markarian 297 and 325. Their velocity dispersions in the Hα emission line (32-41 km s−1) are larger by about 2 or more than those of the so-called giant HII regions in nearby spiral or irregular galaxies.
Evolution of Galaxies with Periodic Star Formation
Authors: Ikeuchi Satoru
Published: June 2019

Interchange processes in the interstellar medium, which is composed of diffuse gas, small clouds and giant molecular clouds are examined. It is stressed that the formation of giant molecular clouds through gravitational instability of a cloud ensemble leads to periodic star formation. The evolution of galaxies with such periodic star formation episodes is studied, especially paying attention to the effect of gas infall.
Evolution of the Galactic Halo and Disk
Authors: Gilmore Gerard
Published: June 2019

Correlations between stellar kinematics and chemical abundances are fossil evidence for evolutionary connections between Galactic structural components. Extensive stellar surveys show that the only tolerably clear distinction between galactic components appears in the distributions of specific angular momentum. Here the stellar metal-poor halo and the metal-rich bulge are indistinguishable from each other, as are the thick disk and the old disk. Each pair is very distinct from the other. This leads to an evolutionary model in which the metal-poor stellar halo evolves into the inner bulge, while the thick disk is a precursor to the thin disk. These evolutionary sequences are distinct. The galaxy is made of two discrete “populations”, one of low and one of high angular momentum. Some (minor?) complexity is added to this picture by the debris of late and continuing mergers, which will be especially important in the outer stellar halo.
Galaxy Evolution from Deep Galaxy Counts
Authors: Gardner J. P.
Published: June 2019

We present deep galaxy number counts and colours of K – band selected galaxy surveys. We argue that primeval galaxies are present within the survey data, but have remained unidentified. There are few objects with the colours of an L∗ elliptical galaxy at a redshift of z ≈ 1, in contradiction to standard luminosity evolution models. We present K – band photometry of the objects in a spectroscopic redshift survey selected at 21 < B < 22.5. The absolute K magnitudes of the galaxies are consistent with the no-evolution or pure luminosity evolution models. The excess faint blue galaxies seen in the B – band number counts at intermediate magnitudes are a result of a low normalization, and do not dominate the population until B ≈ 25. Extreme merging or excess dwarf models are not needed at z < 1.
Stellar Dating and Formation of Galactic Spheroids
Authors: Renzini Alvio
Published: June 2019

In recent years a view spread widely according to which spheroidal stellar systems are not as old as argued by Baade forty years ago and for a long time given for granted. In this – more modern view – most galactic bulges may form late, e.g. as a spontaneous corruption of disks, and most ellipticals may seemingly be late comers, perhaps the result of merging spirals.
Cepheus OB3: Search for Faint Members
Authors: Jordi C. , Trullols E. , Galadí-Enríquez D. , Lahulla F.
Published: June 2019

Johnson UBVRI CCD-photometry was performed for 18 fields (3′×4.4′) in the association Cepheus OB3 using the 1.23m telescope of CAHA at Calar Alto (Almería, Spain). A total of 1055 stars was detected and the sample is complete down to V ≈ 19mag, although only 130 stars were measured with the five filters.
Luminosity and Mass Functions for the Pleiades from the Schmidt Survey
Authors: Schilbach E. , Meusinger H. , Souchay J.
Published: June 2019

From MAMA measurements of Tautenburg and OCA Schmidt plates we obtained proper motions and photographic UBVR photometry for ca. 45 000 stars up to B = 19 mag within a 17 square degree region in the Pleiades. An accuracy of 0.6 mag and 2 mas/year was estimated for magnitudes and proper motions, respectively. A sample of 554 cluster members was separated by use of both astrometric and photometric information on stars.