bluuebunny/crossref_metadata_2025 huggingface dataset:
NGC 7027: New 7.8–20.0 μm Array Camera and Hα/Hβ CCD Image Analysis of Dust, PAH and Ionized Gas Distribution
Authors: Gezari D. Y. , Thornley M. D. , Heap S. R. , Shore S. N. , Varosi F. , Meatheringham S. J. , Maran S. P.
Published: June 2019

Infrared array camera images of the planetary nebula NGC7027 at seven wavelenghts between 7.8 and 20μm taken at the IRTF telescope are compared to Hα and Hβ images obtained at the CFHT, and published 2-, 6-, and 20-cm VLA maps, all made with better than ∼ 1 arcsec resolution. The mid-infrared images have also been deconvolved using the Maximum Residual Likelihood algorithm to show structural details on the ∼ 0.3 arcsec scale. The visible, infrared and radio images are aligned with ±0.2 arcsec astrometric precision using common features and visible stars. Image algebra can then be readily performed. The images are analysed to determine the spatial distribution of poly cyclic aromatic hydrocarbon (PAH) grains and ionized gas relative to the continuum dust emission. The results show the extent of the mid-infrared dust continuum, the PAH emission features at 8.65 and 11.25μm, and would reveal any contribution from 9.8 μm “silicate” emission. The optically thicker 20-cm emission more closely resembles the extinction-corrected Hα distribution. The large grains giving rise to the visible extinction (derived from the Hα/Hβ ratio) are distribued differently from the mid-infrared and ionized gaz, indicating the location of the outer cold dust. The 11.6μm image could contain both PAH and continuum grain emission, and we have attempted to separate the two components. It appears that the overall emission distributions are quite similar for all the infrared wavelengths, so the various dust constituents are generally uniformly mixed. However there are indications that the 11.6μm PAH emission distribution is patchy and not identical to the continuum dust, although not distinctly different in radial distance from the center. The ionized gas distribution peaks inside that of the dust continuum. The visible/infrared/radio spatial analysis, and color indices calculated from the infrared images, are used to develop a detailed new morphological model of NGC7027 based on this comprehensive multi-wavelength data set.
The Third Dredge-up: Status and Problems
Authors: Lattanzio J.C.
Published: June 2019

In this paper I review our understanding of the third dredge-up phenomenon and the nucleosynthesis which occurs during thermally-pulsing AGB evolution.
Spline Fits: Modelling the Observations
Authors: Andronov I.L.
Published: June 2019

The main results on the elaboration of the algorithms and programs for the search of the ‘hidden periodicities’ in the ‘unevenly spaced’ data, are discussed. They are mainly based on the application of the cubic spline-functions practically for all purposed of the variable star research — period determination, approximation of the phase curve, search for the possible period changes and/or the shape of the phase curve, detection of the periodic components in the case of the multi-harmonic oscillations, restoration of the smoothed function by removing the ‘apparat function’, numerical integration etc. Contrary to the commonly used splines with the arguments of the basic points coinciding with that of the real observations, we use the smoothing by the spline with the number of the basic points m, which is smaller than the number of the observations n. The main expressions for the corresponding fitting curves and their statistical properties were published by Andronov (1988, 1989), as well as the FORTRAN programs for the fits and the integration (Andronov, 1986, 1987, respectively).
The Galactic Distribution of O-Rich AGB Stars
Authors: Jiang B.W. , Hu J.Y.
Published: June 2019

In 1976 Georgelin et al.(1976) combined optical and radio observational data of HII regions to study the structure of our Galaxy. The distance of each HII region can be obtained from its radio continuum flux caused by free-free emission and the flux of the Balmer lines with high accuracy. The results clearly show three arms and are used to draw the spiral structure of our Galaxy. It is commonly accepted now.
Mid-IR (8–13μm) Images of Proto-Planetary Nebulae
Authors: Meixner M. , Arens J.F. , Jernigan J.G. , Skinner C.J. , Hawkins G.
Published: June 2019

We present mid-IR (8–13μm) images of dust in seven proto-planetary nebulae (PPN), GL2343, HD 161796, 89 Her, OH 0739–1435, CRL2688, IRAS 22272+5435, and CRL618. The images were taken at UKIRT and the IRTF with the Berkeley mid-IR camera which was developed at the Space Sci. Lab. in UC Berkeley and is supported by IGPP and LEA, LLNL. The results presented here are part of an on-going mid-IR imaging project to study the morphological development of a star as it evolves from the Asymptotic Giant Branch (AGB) to the planetary nebula (PN) stage. In particular, we aim to establish when non-spherical symmetry which is evident in so many PN arises. Four of the objects are oxygen rich. Of these, GL2343 (Fig. 1) and HD 161796 are found to have spherical dust shells in the mid-IR with diameters of 6.″ 7 and 3″, respectively. OH 0739 is marginally resolved, but has a hint of elongation that is aligned with the bipolar nebula evident in the near-IR. 89 Her is unresolved at 1.″ 1 resolution. 89 Her, HD 161796 and GL2343, all high latitude supergiants, appear to form an evolutionary sequence as evidenced by the size of their circumstellar dust shells. Three of the objects are carbon rich. CRL2688 and IRAS 22272 +5435 are found to have elongated structures which suggest a bipolar morphology. CRL 618 is unresolved at 1.″ 7, but is known to be bipolar from optical studies. Hence, with the exception of OH 0739, a known binary, the oxygen rich PPN have spherical dust shells while the carbon rich have bipolar dust shells. Our small number of observations do not provide solid statistics; however, this trend suggests that nebula bipolarity is linked to carbon-rich chemistry.
Axially Symmetric Dynamics of PNe
Authors: Wang Lifan
Published: June 2019

Following Kahn & West (1985), we investigate the formation of PNe in the slow and fast wind interaction scheme by assuming the slow wind axially symmetric. We have further assumed that the mass loss rate for the slow wind is not steady. It is found that the final morphology of the nebula depends not only upon the initial degrees of the seed asymmetry in the slow wind, but also upon the time variations of the mass loss rate. As an example, we show in some detail the case where the central star first blows an axially symmetric slow wind during its red giant stage, this wind is followed by a superwind while the star is on the AGB, these slow wind is later overtaken and shaped by the fast wind during the post-AGB branch. It is found that a small initial asymmetry can be amplified and reproduces the various observed morphologies of the PNe.
LSIV −12° 111 – A Newly Emerging Halo Planetary Nebula
Authors: Conlon E.S. , Dufton P.L. , Keenan F.P. , McCausland R.J.H.
Published: June 2019

We report on multi-wavelength observations of a young halo planetary nebula, LSIV −12° 111. This object was previously classified as an emission-line young B-type star but a model atmosphere abundance analysis of high resolution optical spectra revealed it to be an evolved object, probably in the post-asymptotic giant branch (post-AGB) evolutionary phase. The presence of an infrared excess and low excitation nebular emission lines implies that the central star may have just started to photoionize the remnant (AGB) circumstellar material. Here we discuss the nebular and dust properties of LSIV −12° 111 and re-determine some metal abundances for the central star. These results are used to constrain the evolutionary status of this unique halo planetary nebula.
Search for the Young Planetary Nebulae. Preliminary Results
Authors: Kondratjeva L.N.
Published: June 2019

Some criteria based on the model calculations and observational data were used to choose preplanetaries and young planetary nebulae. Observational results for the object TH4–4 are presented. The spectral and photometric variations of TH4–4 are discussed.
About the Suspected Very Young PN IRAS 17516-2525
Authors: Käufl Hans Ulrich , Stanghellini Letizia
Published: June 2019

Infrared photometry suggests that IRAS 17516-2525 is in transition from the AGB to a young PN (Van der Veen et al. 1989a, b, Manchado et al. 1989). IR spectra (van der Veen et al. 1989b, Käufl et al. 1992) revealed that the object has an ionized core. Optical observations show a weak Hα emitting unresolved object (Käufl et al. 1992) at the coordinates (α1950 : 17h51m37.8s, δ1950 : −25° 25′ 58″) suggested by van der Veen et al. (1989a). The spectrum between 2.0 and 2.4μm shows e.g. Brγ, 2.0875μm (unidentified) or the NaI-doublet but no molecular Hydrogen (present in other compact PNs). The ratio of Pfβ to Brα (hardly affected by extinction, insensitive to electron density and temperature) has been studied in IRAS 17516-2525 and Hen1044. For Hen1044 we find this ratio to be in accordance with theoretical calculations (Hummer and Storey, 1987). For IRAS 17516-2525, however, Pfβ is approximately twice as strong. Hence presumably Hen1044 is optically thin whereas IRAS 17516-2525 is optically thick at λ ≈4–5μm. Line fluxes appear to be constant over a time scale of 4 years. If the visual extinction AV in the object is ≥ 2mag than the infrared luminosity equals the total luminosity (i.e. L = 1400L⊙ ∗ (distance/kpc)2). A main-sequence object accidentally extincted by an intervening cloud can be excluded because the observed line-width of Brα (≈ 40km/s, Van der Veen et al. 1989a) is too small as compared to that of O-stars (≈1000km/s, Käufl, 1992). Assuming an expansion-velocity of ≈ 20km/s the stellar appearance constrains dynamic age and size (age ≤ 360y ∗ distance/kpc, size ≤ 1500AU ∗ distance/kpc). A pre-main sequence object can also be excluded. The max. luminosity (LPMS ≤ 5000L⊙) then requires the object to be closer than 2 kpc where it should be resolvable. In conclusion the observational evidence strongly suggests that IRAS 17516-2525 represents the searched ‘missing link’ between AGB stars and young compact Planetary Nebulae.
Linear Pulsation Periods of the Post-AGB Stars
Authors: Takeuti M. , Takano R. , Tamura S.
Published: June 2019

There may exist stars during and just after the asymptotic giant branch (AGB) stage. V441 (89) is a candidate star. Fernie and Sasselov (1989) have discussed the evolutionary changes of the pulsation periods based on those of the effective temperature, to compare those with observational data. They used Worell's theorical results (Worell 1986) and have found that the observational changes of the period and the colors are too small compared with the theorical values. To examine the effect of opacities on the pulsations periods, we calculate the periods based on new opacities (OPAL, Iglesias and Rogers 1991), and compare them with the data reported previously.
Stripping of a Planetary Nebula from the Globular Cluster M22
Authors: Borkowski K.J. , Harrington J.P. , Tsvetanov Z.
Published: June 2019

High-spatial resolution imaging in the [O III] λ5007 line of a planetary nebula (PN) in the globular cluster M22 reveals a strongly asymmetric (a half-moon shaped) nebular morphology. We confirm that this peculiar morphology is caused by the distortion of stellar ejecta by the ram pressure of the ambient interstellar medium (ISM) through which the cluster is moving with a high velocity of 200 km s−1. Bright emission knots visible in the leading (upstream) nebular section confirm theoretical expectations that the shell should have been fragmented by the Rayleigh-Taylor instability. Stripping of the PN from M22 by the ambient ISM is the first direct evidence for removal of gas from globular clusters. M22 is located at a favourable location for the ram-pressure stripping to be effective, only 400 pc below the Galactic plane, well within a 2 kpc thick layer of ionized gas enveloping the plane. Ionized (possibly neutral) gas in this layer, with a hydrogen density of ∼ 0.1 cm−3, is responsible for the observed interaction.
Morphology & Kinematics of the ‘Born–Again’ Planetary Abell 78
Authors: Clegg R.E.S. , Devaney M.N. , Doel A.P. , Dunlop C.N. , Major J.V. , Myers R.M. , Sharples R.M.
Published: June 2019

Abell 78 is one of a group of planetaries having an old, H–rich nebula surrounding a hot star which has more recently ejected highly–processed, H–deficient material. The A78 central star has O VI emission lines and a 3700 km s−1 hot wind, and is surrounded by knots of very dusty, H-deficient material. These objects are thought to have suffered a late helium shell flash which resulted in the central star (then a white dwarf) returning to the AGB and ejecting highly-processed material.
The IUE Ultraviolet Spectrum of PC 11
Authors: Parthasarathy M. , Pottasch S.R. , Clavel J.
Published: June 2019

PC 11 (HD 149427, PK 331-5 1) is classified as a young planetary nebula with strong OIII 4363Å and a Zanstra temperature of TZ = 27000K. It is also classified as (D′ — type) yellow symbiotic star with A — F type companion. It is an IRAS source with detached cold dust with far intrared (IRAS) colours similar to planetary nebulae. The IUE short wavelength (SWP) spectra show emission lines due to OIII] (1661/1666Å). NIII] (1746/1754Å) CIII] (1907/1909Å). The OIII] and NIII] emission lines show significant variation. Variation in the strength of CIII] is not very significant. The strength of OIII] has decreased and NIII] has increased. The long wavelength (LWP) spectrum shows stellar continuum (A-F) and absorption lines due Mg II 2800Å feature. It also show emission lines at 2772Å (?) 3133Å −3140Å (very strong) (OIII, [FeV], 3209Å (He II?) ([FEII]). The variation in the strength of emission line due OIII] and NIII] and the presence of stellar continuum (A-F) suggests that the central star of PC 11 is a binary.
On the Photometric Behaviour of the Central Star of the Planetary Nebula Sh2–71
Authors: Jurcsik J.
Published: June 2019

The central star of Sh2–71 was observed with the lm telescope using UBV(RI)c photometric system at Konkoly Observatory in the seasons of 1990–92. A period of 68d.06 was found with variable amplitude and/or lightcurve shape. The amplitude is high, close to 1 magnitude. On the basis of old photographic observations (Kohoutek 1979) this period has not changed during the century. No significant colour variation was detected, but the nebular contamination should distort the colour curves. According to the five colour data the central object is a highly reddened B5 dwarf about 1700 pc distant. The nebular properties, however, indicate an evolved, higher mass, lower luminosity exciting source, therefore it is plausible to regard the central object as a binary. The light variation might be caused by obscuration of the B star by outflowing matter from the true nucleus. Bipolar outflow of 3″ dimension has been detected on high dispersion Hα spectra of the central star (Sabbadin et al. 1985; Cuesta et al. 1990). Further spectroscopic observations are highly needed in order to find the exact description of the system.
Diagnostic Diagrams for Planetary Nebulae and Symbiotic Stars
Authors: Gutierrez-Moreno A. , Moreno H. , Cortes G.
Published: June 2019

One of us (Gutiérrez-Moreno 1988) presented some time ago a preliminary version of two diagrams for separating planetary nebulae (PN) from symbiotic stars (SS); tnese diagrams are based on the strength of [O III] lines λλ4363, 5007. Now a new version is presented, which includes more objects and uses measured total intensities corrected by reddening.
Synthetic P-AGB Evolution
Authors: Stanghellini Letizia , Renzini Alvio
Published: June 2019

Extensive Montecarlo simulations of Post-Asymptotic Giant Branch (P-AGB) populations have been constructed, exploring the effects of various assumptions on synthetic H-R diagrams, luminosity functions, and inferred mass distributions. Such assumptions include the IMF, the initial mass-final mass relation, the AGB to PN transition time, the duration of the planetary nebula (PN) stage, etc. We have also investigated how the observational errors in luminosity and temperature propagate into the inferred mass distribution of the P-AGB stars.
The Central Stars of He 2–131 and He 2–138: Photometric Variations
Authors: Hutton R. G. , Méndez R. H.
Published: June 2019

The central stars of the planetary nebulae He 2–131 and He 2–138 show variations in their visual magnitudes, with amplitudes of about 0.1 mag. and time scales of a few hours. This behavior appears to be very similar to that exhibited by the central stars of IC 418 and IC 4593. These four central stars have several other characteristics in common: a relatively low effective temperature, between 27000 and 40000 K; clear spectroscopic evidences of mass loss, both in the ultraviolet (IUE) and visible spectral regions; and short-term spectroscopic variability, in the form of radial velocity variations and/or of substantial changes in emission and P-Cygni-type line profiles. None of these central stars has shown convincing evidence of binarity; we attribute their behavior to variations in the stellar winds.
A New PG 1159-Type Central Star Discovered in the ROSAT XRT All Sky Survey: Non-LTE Analysis of X-Ray and Optical Spectra
Authors: Werner K. , Motch C. , Pakull M.
Published: June 2019

We report on the discovery of a new PG 1159 star in the ROSAT XRT all sky survey and give results of a model atmosphere analysis. The X-ray source RX J2117.1+3412 is relatively faint (0.33 cnts−1) and extremely soft. Ground based optical follow-up spectroscopy (OHP, France) proofs its PG 1159 nature: It belongs to the “low gravity emission” spectral subtype. Optically, it is the second brightest PG1159 star. CCD [O III] imagery reveals that the star is surrounded by an old arc-shaped planetary nebula of faint surface brightness. The spectral analysis of the central star was performed with non-LTE line blanketed model atmospheres (Werner 1992). We find a complete agreement between the atmospheric parameters determined at optical wavelengths and in the ROSAT PSPC energy range.
The Low Luminosity Central Star of the PN ESO166-21
Authors: Ruiz M.T. , Peña M. , Torres-Peimbert
Published: June 2019

We present low dispersion UV and optical spectrophotometry of the central star of the PN ES0166–21. The stellar spectrum, from 1200 to 6600 Å, is a featureless continuum. The energy distribution is consistent with a black body of 120, 000 ± 20, 000K. The observed visual magnitude is 18.1.
Why are Planetary Nebulae Poor Distance Indicators?
Authors: Tammann G.A.
Published: June 2019

It is shown from multiple evidence that the λ 5007 Å luminosity of the brightest shells of planetary nebulae has intrinsic scatter, which is well approximated for the brightest objects by an exponential luminosity function, as proposed by Bottinelli et al. (1991). The resulting open-ended luminosity function weakens the usefulness of planetary nebulae as distance indicators.
Planetary Nebula Birth Rates in the Galaxy and Other Galaxies
Authors: Peimbert Manuel
Published: June 2019

A review is presented of PN birth rates. The observational determinations for other galaxies are compared with theoretical predictions based on stellar evolution models. The galactic birth rate is derived for different distance scales and is compared with the predicted one from galactic models of the solar neighborhood and with those determined for other galaxies; to reach agreement between observations and predictions long distance scales to PN have to be adopted. The total number of PN is estimated for the Galaxy and other galaxies.
How to Model the Chemical Evolution of Galaxies
Authors: Köppen Joachim
Published: June 2019

For a first interpretation of the comparison of observational data, the crude “Simple Model” of chemical evolution is quite useful. Since it has well been described in the literature (e.g. Pagel and Patchett 1975, Tinsley 1980), let us here just review the assumptions and whether they are satisfied:

1.

The galaxy is a closed system, with no exchange of matter with its surroundings: For the solar neighbourhood this probably is not true (the infamous Gdwarf-“problem”, Pagel 1989b). For the Magellanic Clouds this is most certainly wrong, because of the presence of the Inter-Cloud Region and the Magellanic Stream, and evidence for interaction with each other and the Galaxy as well (cf. e.g. Westerlund 1990).

2.

It initially consists entirely of gas (without loss of generality of primordial composition): This is good approximation also for models with gas infall, as long as the infall occurs with a time scale shorter than the star formation time scale.

3.

The metal production of the average stellar generation (the yield y) is constant with time: Initially, it is reasonable to make this assumption. For tables of the oxygen yield see Koppen and Arimoto (1991).

4.

The metal rich gas ejected by the stars is completely mixed with the ambient gas. To neglect the finite stellar life times (“instantaneous recycling approximation”) is appropriate for elements synthesized in stars whose life time is much shorter than the star formation time scale, such as oxygen, neon, sulphur, and argon.

5.

The gas is well mixed at all times: We don't know. The dispersion of H II region abundances may give an indication. In the Magellanic Clouds Dufour (1984) finds quite a low value (±0.08 dex for oyxgen).
The Radial Velocities of Planetary Nebulae in NGC 3379
Authors: Ciardullo Robin , Jacoby George
Published: June 2019

Several authors have analyzed the kinematics of elliptical galaxies using surface photometry in combination with absorption line velocity dispersion measurements. However, these analyses never explore the halos of galaxies, since the best absorption line measurements extend only ∼1 re. The only way to extend our knowledge of stellar kinematics to larger radii is to use the emission lines of planetary nebula for radial velocity measurements.
A CCD Modulation Detector for a Second Hipparcos Mission
Authors: Høg E. , Lindegren L.
Published: June 2019

A CCD modulation detector for a possible Hipparcos-2 mission is described. It is at least 1000 times more light efficient than the image dissector tube system used in the current Hipparcos mission. A beam combiner telescope with 29 cm aperture diameter could measure all 15 million stars brighter than 14th magnitude, providing accurate multi-colour photometry in addition to the astrometric parameters. Using two telescopes with different basic angles will further improve the rigidity of the resulting system of positions and proper motions. An accuracy of 0.5 milli-arcsec up to 10th magnitude is expected for a 2.5 year mission. The modulating grid is imaged on a CCD performing a ‘cophased integration’ of nine separate images of the whole field of view, each image representing a different part of the modulation period.
CCD Parallaxes for Southern Very Low Luminosity Stars
Authors: Ianna Philip A.
Published: June 2019

Trigonometric parallaxes based on CCD observations are presented here for six southern very late-type M dwarf stars and three white dwarfs. The M dwarfs RG0050-2722, ESO207-61, MH2115-4518, MH2124-4228, and LHS3003 are among the very lowest luminosity stars known.
Improvement of Type II Photoelectric Astrolabe and Primary Results
Authors: Gang Zhao , Jianwei Zhang
Published: June 2019

Utilizing the photon counter to register the star through the 60° altitude and a microcomputer to control the telescope pointing, the automatization was attained in the observation of type II photoelectric astrolabe. The limiting magnitude of the improved astrolabe is up to 11.0 and the precision of single determination is ± 0.2 arc — sec. This automatic instrument is more powerful in improving the FK5 system and expanding the current optical celestial system into faint stars.
Realization of a Single Image with Autocollimation for PHA I
Authors: Jiayan Xu , Hongqi Wang , Zhiwu Zhang
Published: June 2019

The First PHotoelectric Astrolabe (PHA I) of China was installed at Shaanxi Obs. in 1971 and came into use later. PHA I has been operating automatically since 1986. Now it is being revised by using a single image with autocollimation, equipped with photon counting system and a tracking diaphragm with a small window to follow the star in zenith direction, which would cut off the most light of the night sky. With all these three approaches, PHA I could improve its limiting magnitude from mag. 6 to mag. 11 or even fainter.
Maximum Likelihood Estimation of Digital Image Center
Authors: Chun-Lin Lu
Published: June 2019

A algorithm for digital image centering with the maximum likelihood method is described. The astrometric accuracy of this algorithm is similar to the two-dimensional Gaussian fitting. For saturated images, this algorithm is better than the Gaussian fitting. With the maximum likelihood method, some systematic effect, such as coma and magnitude equation, can be reduced significantly.
CERGA Photoelectric Astrolabe — Computational and Instrumental Improvements
Authors: Chauvineau B. , Journet A. , Vigouroux G. , Kovalevsky J. , Billaud G. , Boche R. , Furia M.
Published: June 2019

The compilation of three years of observations by the improved photoelectric astrolabe of CERGA has provided a star catalogue with an internal precision of 0.03″ in right ascension and 0.04″ in declination for 47 stars and a similar precision for 82 other stars solved only for right ascension (Vigouroux et al., 1992). The classical group reduction was used. External comparisons with preliminary HIPPARCOS positions showed that these numbers represent the accuracy of the catalogue. However, many changes in the instrument and in the reduction procedures are contemplated that should bring new significant improvements in these results.
Eurasian-Pacific-N. American Plate Motions from Very Long Baseline Interferometry
Authors: Mao Ailin , Qian Zhihan
Published: June 2019

We use the baseline variation rates, which are obtained by the VLBI measuring in the past years (1979. /-1991.1), to estimate the relative motions among Eurasian, Pacific and North American plates. A comparion with the geological-based models has been made. In order to strengthen the VLBI constraints on the Euler vectors, we estimate the velocities of unstable stations in addition to the Euler vectors.
Space VLBI Project VSOP
Authors: Inoue Makoto
Published: June 2019

A space VLBI satellite is planed to be launched in 1995 by the Institute of Space and Astronautical Science (ISAS), Japan. Together with this satellite, a worldwide collaborative project named the VLBI Space Observatory Program (VSOP) is under developed. Although the project is oriented to imaging mission for compact cores of active galactic nuclei and maser sources, it will open new aspect on all of VLBI applications. The basic design and parameters of VSOP project are reviewed.
Comparison and Calculation of Different Atmospheric Delay Models Using Atmospheric Parameters of VLBI Stations of China
Authors: Yang Zhigen
Published: June 2019

The values of the atmospheric time delay for the “Chao”, “Marini” and “CfA−2.2” mapping function are calculated by using the atmospheric parameters in summer and winter at Shanghai, Kunming and Urumqi station respectively. A comparison among these values shows that the derivations of “Marini” from “Chao” and “CfA” are relatively large. On the other hand, the difference of values between the “Chao” and the “CfA” in the case of ∊ = 40° ∼ 10°, which is the average for the three stations, is from +1 mm to +47 mm for the “wet” part of the delay in summer, while is from −2 mm to −28 mm for the “dry” part in winter. For the case of low elevation angle ɛ ≐ 5°, the difference for the “wet” part can be about 400 mm in summer. Therefore, it is indispensable to make a further comparison between “Chao” and “CfA” mapping function by using the data of VLBI observations, in order to make a better revision to the adopted models of atmospheric delay.

The monthly averages of the height of tropopause ht and the tropospheric temperature lapse rate βt for the three stations mentioned above are used to calculate the dry atmospheric delay by the “CfA” mapping function. The results show that the amplitudes of the annual changing of delay dτa, which is caused by ht and βt for the case of ∊ = 20° ∼ 10° at Urumqi station, are about 1 ∼ 5 mm and 2 ∼ 15 mm respectively. Therefore, taking the parameters of ht and βt of the stations into account in “CfA” model, instead of using fixed constants, would be much favourable for the requirements of 1 ps precision of VLBI physical models.
High-Precision Parallaxes and Their Astrophysical Applications
Authors: Lai Wan
Published: June 2019

As demonstrated by USNO CCD parallax program, a CCD attached to a modest aperature telescope is capable of measuring stellar trigonometric parallax to a precision better than 1.0 mas. consequently, many objects previously regarded as being too distant for ground-based trigonometric distance determinations can now be considered.

In this paper we show the High-precision parallaxes will provide a very good opportunity for the refinement of H-R digrammes and the calibration of luminosity criteria, we also refer to the open cluster and to determination of accurate stellar masses from close binanies.
The Stellar Kinematics in the Main Meridional Section of the Galaxy
Authors: Kharchenko N. V.
Published: June 2019

In the framework of the programme of studying the meridional section of the Galaxy (MEGA) the catalogue of stellar data (about 26500 stars) had been compiled and investigated. The main part of the catalogue consist of the proper motions of stars with respect to the galaxies. The stellar kinematical characteristics in the direction of the galactic rotation, the parameters of velocity ellipsoid and the relation between kinematical, spatial and chemical properties of stellar populations have been determined.
Is the Chandler Period Stable?
Authors: Buxi Gao
Published: June 2019

The problem on Chandler period is an unsolved one. Several authors suggested a hypothesis that the Chandler wobble is only one free period which slightly changes in time and is amplitude-dependent. In this paper we shall make the hypothesis more rigorous than that has been carried yet. A new deconvolution method for Fourier transform is suggested. Using this method the polar motion data are analysed. The analysis results are shown; the Chandler period is not stable and is indeed amplitude-dependent. The probable explanation for the amplitude-dependent of Chandler period is that, which might be caused by non-equilibrium response of the ocean.
Effects of Mantle Anelasticity on the Chandler Wobble
Authors: Yaozhong Zhu
Published: June 2019

On the basis of the perturbation principles of the normal mode and Love numbers, the theoretical Q of the Chandler wobble is derived by assuming that the wobble energy is totally dissipated within the mantle and by using Zschau's mantle rheology model. The results show that mantle anelasticity is likely to be the most important dissipative source of the Chandler wobble energy, and the theoretical Chandler Q is 71. Finally, the parameter α of the absorption band model is calculated, and the applicability of the model is discussed as well.
Issues of Time for Reference Systems
Authors: Seidelmann P. K.
Published: June 2019

At the International Astronomical Union General Assembly in 1991 the terminologies Geocentric Coordinate Time (TCG) and Barycentric Coordinate Time (TCB) were introduced as the time coordinates of four dimensional geocentric and barycentric coordinate systems, respectively. The reasons for these time-like arguments and their applications will be discussed. The relationships between the different time-like arguments will be discussed along with their applications and relationships to the astronomical constants.

Since these time-like arguments have secular differences, there are new issues to be resolved. These new issues include the definition of the epoch J2000.0, relationship between mean and apparent sidereal time, the time-like argument for specifying constants, the definition and future use of ephemeris time, delta T values and the transition to, or future use of, TCG, TCB and TDB.
Departure Point, Earth's Rate of Rotation and Coordinate Transformation in Quasi-Inertial Geocentric Equatorial Coordinate System (QIGECS)
Authors: Yan H.J. , Groten E.
Published: June 2019

The paper summarizes the discussion on the origin of right-ascension and puts forward new arguments in view of high-precision Geodesy and Astrometry. From the movement of the Celestial Departure Point, the classical right-ascension precession might be amended by an additional term −0s.000257/century originating from the nutation-precession interaction movement. A similar term might also be introduced in the maintenance of a terrestrial reference system, while the concept of a Terrestrial Departure Point is considered. The definition of the Earth's rate of rotation in an inertial or quasi-inertial system is reviewed. A periodic erroneous term of maximum amplitude 2.65mas is pointed out in the conventional transfer relation between CRS and TRS, that can for its main part be compensated by introducing the periodic terms of Woolard's equation of the equinox.
Prospects for the Application of a Mobile VLBI System in China
Authors: Jianqing Cai , Hanlin Xia
Published: June 2019

Based on the present status and projects of Chinese VLBI and SLR fixed stations, the applications of a mobile VLBI system are investigated in establishing a Chinese high accuracy geodetic VLBI network and terrestrial reference frame.
The Hertzsprung-Russell diagrams for open clusters
Authors: Barkhatova K. A.
Published: June 2019

The most important relationship between physical characteristics of stars is the spectrum-luminosity correlation. Investigating the character of this correlation for stars of open clusters, Trumpler has worked out a classification of clusters according to their spectral composition.
A preliminary color-magnitude diagram for late-type stars in the solar neighborhood
Authors: Wilson O. C.
Published: June 2019

Modern photoelectric techniques yield magnitudes and colors of stars with accuracies of the order of a few thousandths and a few hundredths of a magnitude respectively. Hence for star clusters it is possible to derive highly accurate color-magnitude arrays since all of the members of a cluster may be considered to be at the same distance from the observer. It is much more difficult to do this for the nearby stars where all of the objects concerned are at different, and often poorly determined, distances. If one depends upon trigonometric parallaxes, the bulk of the reliable individual values will refer to main sequence stars, and while the mean luminosities of brighter stars are given reasonably well by this method, the scatter introduced into a color-magnitude array by using individual trigonometrically determined luminosities could obscure important features. Somewhat similar objections could be raised against the use of the usual spectroscopic parallaxes which also should be quite good for the main sequence but undoubtedly exhibit appreciable scatter for some, at least, of the brighter stars.
Mass loss in red giants
Authors: Deutsch Armin J.
Published: June 2019

On high-dispersion spectrograms of some luminous M giants, the zero-volt lines of all abundant atoms and ions are double. (Fig. 1 (a), Pl. I, p. 112). This spectroscopic peculiarity was discovered by W. S. Adams and Miss MacCormack (1935), who wrote that “a possible explanation of the origin of the abnormal lines…… may be an envelope of gas surrounding the stars and expanding with a moderate velocity”. Recently it was found that some of the abnormal lines which occur in the M 5 II star α Herculis can also be seen in the spectrum of its visual companion, a giant G-type star. In this system, it is clear that the Adams-MacCormack model is correct: both stars are enveloped in gas that has been ejected from the M star (Fig. 2). Moreover, the circumstellar envelope of α Herculis must measure at least 2000 astronomical units in diameter, and in it the gas velocity exceeds the velocity of escape. The M star is clearly losing mass to the interstellar medium at a rate that has been estimated to be a about 10−7 solar masses per year.
Isophote Shapes
Authors: Jedrzejewski R. I.
Published: June 2019

The shapes of the isophotes of elliptical galaxies are discussed. Ellipticity and position angle variations with distance from the centres of galaxies are described, as well as deviations from perfectly elliptical shape. The factors contributing to these deviations, in particular edge-on disks and boxiness, are described and portrayed.
Distribution of Light: Outer Regions
Authors: Capaccioli Massimo
Published: June 2019

The data base of photometric properties of galaxies has grown enormously in the last few years. Surveys in various colors, detailed studies of selected objects, and a swarm of papers with underlying photometric information have invaded the market, fostered by advances in the technology of observations and by improvements and wider availability of reduction facilities. A bibliographical compilation, of great use in the jungle of old and modern references, has been published by Davoust and Pence (1982), and is currently updated (Pence and Davoust 1985).
X-Rays from Elliptical Galaxies
Authors: Fabian A.C. , Thomas P.A.
Published: June 2019

X-ray observations have shown that early-type galaxies contain a hot interstellar medium. This implies that the galaxies have a) a low supernova rate; b) high total gravitational binding masses and c) continuous star formation. Much of the gas in isolated galaxies is probably due to stellar mass-loss. The details of its behaviour are complex.
Star Formation in Cooling Flows
Authors: O'Connell R. W.
Published: June 2019

Star formation, probably with an abnormal initial mass function, represents the most plausible sink for the large amounts of material being accreted by cD galaxies from cooling flows. There are three prominent cases (NGC 1275, PKS 0745-191, and Abell 1795) where cooling flows have apparently induced unusual stellar populations. Recent studies show that about 50% of other accreting cD's have significant ultraviolet excesses. It therefore appears that detectable accretion populations are frequently associated with cooling flows. The questions of the form of the IMF, the fraction of the flow forming stars, and the lifetime of the flow remain open.
Orbits
Authors: Binney James
Published: June 2019

Orbits that respect at least three isolating integrals of motion have very special structures in phase space. The main characteristics of this structure are reviewed, and the concrete examples that are provided by orbits in Stäckel potentials, are discussed. Many orbits in general potentials admit three approximate isolating integrals and closely resemble orbits in Stäckel potentials. If the potential is that of an elliptical galaxy with negligible figure rotation, the overall orbital stucture of the potential differs from that of a Stäckel potential only by the presence of a few unimportant families of resonant orbits. However, this elegant picture is shattered by the introduction of non-negligible figure rotation: though substantial regions of phase space may still be occupied by orbits that individually resemble orbits in Stäckel potentials, the overall orbital structure is radically changed by figure rotation, and in a rotating potential significant portions of phase space are given over to chaotic orbits, quite unlike orbits in Stäckel potentials.
Shells and the Potential Wells of Elliptical Galaxies
Authors: Quinn P.J. , Hernquist Lars
Published: June 2019

A survey of the possible variety of sharp-edged, caustic features that may arise in the collision of galaxies with very different masses and sizes (Hernquist and Quinn 1986a) has shown that in general shells are morphologically very complex. It is therefore not easy to determine the history of the collision that produced the shells nor the properties of the galaxies involved. However, a small number of shell galaxies (notably NGC 3923) have a sufficiently simple and orderly shell distribution that we believe the shells were formed by a chance very symmetric and simple encounter. In such cases we are presented with a unique opportunity to investigate the potential well of an elliptical galaxy over a large range in radius (≃ 0.5re− 20re). An analysis of the NGC 3923 shell system (Hernquist and Quinn 1986b) has shown that a large amount of dark matter is present (Mdark≃ 40Mluminous, r< 17re).
Dynamical Models for Axisymmetric and Triaxial Galaxies
Authors: de Zeeuw Tim
Published: June 2019

Non–spherical dynamical models for galaxies, and the methods for their construction, are reviewed. The theory for two–integral axisymmetric models is reasonably well developed. Stäckel models give considerable insight in the structure of both three–integral axisymmetric models and non–rotating triaxial systems. Triaxial galaxies with appreciable figure rotation require much further study. Applications to elliptical galaxies and the bulges of disk galaxies are discussed.
Stability of Elliptical Galaxies. Theoretical Aspects
Authors: Polyachenko V.L.
Published: June 2019

Stars, which contain more than 90% of the visible matter of the Universe, are organized into systems comprising a hierarchy of different masses and scales: from galactic stellar clusters to clusters of galaxies themselves. Most of the systems in this hierarchic sequence are collisionless: the characteristic time between collisions is much more than typical dynamical times (e.g., the period of oscillations). Various conditions of formation of collisionless gravitating systems leave traces on their main characteristic parameters—such as the angular momentum, the degree of anisotropy, the kind of dependence of the stellar density on coordinates, and so on. The lifetime of a system with a certain set of parameters depends essentially on whether these parameters belong to a region in which the system is stable, or not. If they do, the system may then exist practically without changes for an arbitrarily long time (in terms of the dynamical time scale); if they do not, it must quickly adjust to another, stable state.
The Isophotal Structure of Elliptical Galaxies
Authors: Williams T.B. , Bhattacharya Bidushi
Published: June 2019

We have obtained photographic surface photometry for a large sample of elliptical galaxies. The plates were obtained using the KPNO 0.9 m telescopes with Carnegie image intensifiers and IIIaJ plates. The f/13.5 secondaries were used to obtain a large plate scale: 0.33 arcsec per 20 micron pixel. In addition to the galaxy images, flat fields on cloudy skies and geometrical distortion calibration images of astrometric clusters were obtained. All plates were calibrated with the standard KPNO spot sensitometers. The sample of galaxies contains 75 ellipticals of total mB greater than 13 and north of −300 declination. The plates were digitized on the KPNO PDS microdensitometer by Dr. E. Malumuth. At the present time about 50% of the sample is reduced.
Detailed Surface Photometry of the Dust-Lane Elliptical NGC 6702
Authors: Davoust E. , Capaccioli M. , Lelièvre G. , Nieto J.-L.
Published: June 2019

We present preliminary results of a detailed photometric study of NGC 6702, from high resolution photographs taken at the Cassegrain focus of the Canada-France-Hawaii (CFH) telescope. The luminosity distribution of the galaxy follows an r1/4 law (re* = 11.6″, μe* = 22.17). The axis ratio is 0.75 (corresponding to the morphological type E3) and the position angle of the major axis is 60 and fairly constant. Fig. 1 is an image in intensity of the galaxy, from a 30mn exposure in B. The galaxy is crossed by a dust lane, reported first by Capaccioli et al. (1984).
AM2020–5050: an Elliptical Galaxy with an Outer Ring
Authors: Whitmore Bradley , Schweizer François
Published: June 2019

Photometric and spectroscopic observations show that the inner component of AM2020—5050 is an elliptical galaxy, unlike other polar-ring galaxies which have an SO disk at the center. A comparison of the central velocity dispersion with the rotational velocity in the ring suggests the presence of a nearly spherical gravitational potential. The inner component has a rapidly rotating core with rotational velocities at 3″ substantially higher than at 8″. Although the optical ring is quite narrow, Hα emission is observed all the way through the center of the galaxy, indicating the presence of an extended gaseous disk.
Taurus Observations of S0 Polar Ring Galaxies
Authors: Nicholson R.A. , Taylor K. , Sparks W.B. , Bland J.
Published: June 2019

By use ot the TAURUS imaging Fabry–Perot interferometer (Taylor & Atherton 1980) we have obtained seeing limited two–dimensional velocity, line width and line flux maps of the ionised gas in two polar ring systems.
Line-Strength Gradients in Elliptical Galaxies
Authors: Davies Roger L. , Sadler Elaine M.
Published: June 2019

We have measured line-strength indices as a function of radius in several elliptical galaxies. All of them show strong radial gradients in Mg, but much weaker gradients in Fe and Hβ. The isophotes and contours of constant line-strength have the same flattening. More luminous galaxies have shallower gradients, contrary to the prediction of models of dissipative collapse. Most of the galaxies observed show weak central emission which can partially fill the Balmer absorption lines.
The “Jet” of M89: CCD Surface Photometry
Authors: Clark G. , Plucinsky P. , Ricker G.
Published: June 2019

We have obtained CCD images in R and V of Malin's “jet” in the weakly radio and X-ray active E0 galaxy M89 (NGC4552). the luminosity of this feature is approximately 1/4% of the total luminosity of the galaxy; its color is bluer than that of the whole galaxy with a V-R value smaller by about 0.15 magnitudes. the likely explanation of the feature, which looks more like a proboscis than a jet, is that it is, in the words of the Toomres (1972), a “tidal relic of a close encounter”, seen from a perspective that may hide a drawn out tail.
Stochastic Stellar Orbits and the Shapes of Elliptical Galaxies
Authors: Gerhard Ortwin E.
Published: June 2019

Using Melnikov's method to study the appearance of stochastic orbits in perturbed Stäckel potentials, a correlation is found between the observed shapes of elliptical galaxies and the occurence of mainly regular orbits. Some other potential perturbations giving rise to large regions of stochastic orbits, on the other hand, appear to be inconsistent with observations.
Formal Inversion of the Self–Consistent Problem for Triaxial Galaxies
Authors: Dejonghe Herwig
Published: June 2019

Triaxial separable potentials V(λ, μ,ν) = fλ + fμ + fν ≥ 0, with

admit three constants of the motion (see de Zeeuw 1985 for more details), for which we can take the following set:

Here vλ, and vν are the velocity components in the (λ, μ,ν) coordinate system, and we recognize in E the binding energy per unit mass.
Towards a Self-consistent Model of a Galaxy
Authors: Durodie W.J.L.V. , Kahn F.D.
Published: June 2019

Using a theoretical model for the functional distribution of stars in phase space in a spherically symmetric galactic system, it is found upon solving the fundamental equations of stellar dynamics that the rotation curves produced by the model are flat for large distances within the system. the properties of the stellar orbits within such systems are investigated and an N-ring axially and equatorially symmetric model for simulating its dynamics is presented. Poisson's equation is solved by expanding density and potential in Legendre polynomials (c.f. van Albada and van Gorkom, 1977). It is helped to follow the time development of such a system under various forces.