bluuebunny/crossref_metadata_2025 huggingface dataset:
EVN and MERLIN observations of an OH maser ring and a starburst continuum in III Zw 35
Authors: Pihlström Ylva M. , Conway John E. , Booth Roy S.
Published: June 2019

We report on high-sensitivity EVN and MERLIN observations of the OH maser emission and continuum in the luminous infrared galaxy III Zw 35. Earlier VLBI observations have shown two compact maser clumps containing 40%–50% of the single-dish flux. In addition to these compact masers, we detect more diffuse maser emission which lies in a clear ring structure of radius r ∼ 22 pc. The ring appears inclined to the line of sight and the compact masers occur at the tangent points. This structure suggests that the compact and diffuse masers appear different because of geometrical effects and not pumping or other physical conditions. Our observations reveal a velocity gradient along the western side of the disc which indicates rotation. The 18 cm continuum radiation is resolved into a few unresolved sources, plus more diffuse emission and is broadly consistent with emission originating in a starburst.
EVN Observations of the OH megamaser galaxies Mrk 231 and IC 694
Authors: Klöckner Hans-Rainer , Baan Willem A.
Published: June 2019

We present EVN observations of hydroxyl (OH) main-line emission in two megamaser sources Mrk 231 and IC 694. The observations indicate that the broad maser emission lines originate within the nuclear regions. A single 1667 MHz main-line feature is seen at the nucleus of IC 694. In Mrk 231 both main-lines were observed in an extended “half-circular” region of 150 pc by 50 pc surrounding the radio nucleus.
Maser emissions from comets
Authors: Colom Pierre , Bockelée-Morvan Dominique , Crovisier Jacques , Gérard Éric
Published: June 2019

The 18-cm lines of the OH radical are the only well-documented masers in comets. They have been observed in more than 65 comets since 1973. The good knowledge of their excitation mechanisms and their linear regime allow us to estimate the water production rate and its variation with heliocentric distance from radio observations of OH in comets. Two bright comets, C/1996 B2 (Hyakutake) and C/1995 01 (Hale-Bopp), recently passed perihelion. We give an account of their observing campaigns and of the new insights they provide in the physics of comets. We also discuss the possibility of masering emission for other cometary molecules: H2O, CH, CH3OH.
The puzzle of natural lasers
Authors: Strelnitski Vladimir
Published: June 2019

Hundreds of strong astrophysical masers have been detected since the first, serendipitous detection of such a maser in 1965. Surprisingly, no high-gain natural lasers in the optical domain and only one in the infrared domain have been detected during these decades. What does inhibit natural lasing? An answer is proposed in this presentation.
Diffuse OH in the Milky Way
Authors: Gray M.D. , Masheder M. R. W.
Published: June 2019

We obtain integrated gains for the OH ground-state lines from an exact radiation transfer code with parameters suitable for a large molecular cloud. Results show that the lines are usually formed in NLTE, and that the satellite lines typically show conjugate behaviour. Constraints are set on the OH abundance and kinetic temperature by the requirement that there be no strong maser emission in the main lines.
Bulge Globular Clusters
Authors: Barbuy B. , Ortolani S. , Bica E.
Published: June 2019

The properties of the globular clusters located within 20° × 20° of the Galactic Center are discussed. In particular their spatial distribution, metallicities and ages are presented and discussed in the context of different scenarios of bulge formation.
The Globular Clusters of M31: Keys to its Formation History
Authors: Perrett Kathy , Bridges Terry , Hanes Dave , Irwin Mike , Carter Dave , Brodie Jean , Huchra John , Watson Fred
Published: June 2019

With the ultimate goal of distinguishing between various models describing the formation of galaxy halos (e.g., radial collapse, chaotic mergers), we present the results of a spectroscopic study of the globular cluster system of M31. We have obtained deep, intermediate-resolution spectra for several hundred of the M31 globular clusters using the WYFFOS fibre-fed spectrograph at the William Herschel Telescope. These observations have yielded precise radial velocities and metallicities for over 200 members of the M31 globular cluster population, the vast majority of which represent new data or significant improvements over pre-existing data.
Star Clusters in Irregular Galaxies in the Local Group
Authors: Grebel Eva K.
Published: June 2019

I summarize our knowledge of star clusters and associations in irregular galaxies other than the Magellanic Clouds in the Local Group. Surveys affording complete area coverage at high angular resolution are still lacking. Confirmed globular clusters are known only in NGC 6822 and WLM. Very few dIrrs contain populous or sparse open clusters. There is a pronounced deficiency of intermediate-age and young clusters. Apart from parent galaxy mass, the lack of interactions may be a key reason for the lack of cluster formation in the dIrrs. All dIrrs have one or several short-lived OB associations in the star-forming regions in their centers.
Second Parameter Effects in and between M3 and Palomar 3
Authors: Catelan M. , Rood R. T. , Ferraro F. R.
Published: June 2019

We study the globular clusters M3 and Palomar 3 as a “second parameter (2ndP) pair,” showing that: i) M3 has a surprisingly strong internal 2ndP; ii) The dispersion in mass on the Pal 3 horizontal branch (HB) is intrinsically very small, leading to the most apparent differences in HB morphology between M3 and Pal 3; iii) Ignoring the difference in HB mass dispersion between M3 and Pal 3, their relative HB types can be accounted for by a fairly small difference in age, of order 0.5–1 Gyr.
HST-WFPC2 Observations of the Star Clusters in the Giant HII Regions of M33
Authors: Gyoon Lee Myung , Soo Park Hong , Chul Kim Sang , H. Waller William , Wm. Parker Joel , M. Malumuth Eliot , W. Hodge Paul
Published: June 2019

We present a photometric study of the stars in ionizing star clusters embedded in several giant H II regions of M33 (CC93, IC 142, NGC 595, MA2, NGC 604 and NGC 588). Our photometry is based on the HST-WFPC2 images of these clusters. Color-magnitude diagrams and color-color diagrams of these clusters are obtained and are used for estimating the reddenings and ages of the clusters. The luminosity functions (LFs) and initial mass functions (IMFs) of the massive stars in these clusters are also derived. The slopes of the IMFs range from Γ = −0.5 to −2.1. Interestingly, it is found that the IMFs get steeper with increasing galactocentric distance and with decreasing [O/H] abundance.
Globular Cluster Subpopulations in Early-Type Galaxies: Insights into Galaxy Formation
Authors: P. Brodie Jean
Published: June 2019

New and archival HST images of the globular cluster systems of 17 relatively nearby galaxies and 6 more distant galaxies have been used to establish the characteristics of GC subpopulations over a range of host galaxy morphological type from E5 to Sa. GC color/metallicity, size and luminosity distributions have been examined in the nearby galaxies and color distributions have been determined for the more distant sample. Correlations with parent galaxy properties and trends with galactocentric radius have been explored. Supplemented with Keck spectroscopy, our results are best explained by an in situ formation scenario in which both GC subpopulations formed at early times within the potential well of the protogalaxy, in multiple episodes of star formation. We have also discovered a third population of clusters, fundamentally distinct from the compact red and blue clusters common in early type galaxies.
The Globular Cluster Specific Frequency in NGC 1399 and 4486: A Comparative Study
Authors: C. Forte Juan , Geisler Doug , Kim E. , Gyoon Lee Myung , Ostrov Pablo
Published: June 2019

A two color CCD survey for globular clusters in the galactocentric range from 2 to 7 arcmin from the galaxy centers is presented for NGC 1399 and NGC 4486 (M87), two systems that, for a long time, have been considered as class archetypes of the so called “high specific frequency phenomenon”. The new results, combined with previously published HST data for the inner 2 arcmin, and with a re-discussion of the surface brightness profiles, allow a new estimate of the globular cluster specific frequencies. The resulting SN values cannot be considered as anomalously large and, rather, they are consistent with values obtained for other galaxies with similar morphologies.
Globular Cluster Systems in the Hydra I Galaxy Cluster
Authors: Hilker Michael
Published: June 2019

In this contribution, first results of deep VLT (V,I) photometry in the central region of the Hydra I galaxy cluster are presented. Many star clusters have been identified not only around several early-type galaxies, but also in the intra-cluster field, as far as 250 kpc from the cluster center. Outside the bulges of the central galaxies NGC 3311 and NGC 3309, the intra-cluster globular cluster system is dominated by blue clusters whose spatial distribution is similar to that of the (newly discovered) dwarf galaxies in Hydra I. The color distributions of globular clusters around NGC 3311 and NGC 3309 are multimodal, with a sharp blue peak and a slightly broader distribution of the red cluster population.
Super Star Clusters in M82
Authors: W. O'Connell Robert
Published: June 2019

M82 is the nearest starburst galaxy. It contains two large systems of super star clusters, one being spawned today in the active starforming core, and one produced by an earlier starburst event which coincided with the last orbital passage of its neighbor, M81. The proximity of M82 makes it uniquely valuable for a wide range of studies of massive young clusters and their environments.
The Peculiar Complexes of Star Clusters in Galaxies
Authors: N. Efremov Yuri
Published: June 2019

Existence of complexes of clusters and complexes of isolated stars is the key to understand the cluster and isolated modes of star formation. Examples of such complexes in the LMC are considered. New kind of complexes with the circular shape or including arc-like structures is described, first of all in the LMC and NGC 6946. They may be of other origin than most HI supershells. The system of the giant stellar arcs (partiall spheres seen in projection) in the NE region of the LMC might be formed by GRB events, progenitors of which might be ejected from the massive nearby cluster NGC 1978. Otherwise the arcs might be results of cloud impacts, being concentrate at the NE side of the LMC because this side is leading in the orbital motion of the LMC. The strong arguments are given for the NE (and not Eastward) direction of the LMC movement. Also, the shock wave from a superexplosion might give the shape of the partial sphere to the facing surface of a nearby dense cloud.
Star Formation Properties of 100 Star Formation Complexes in 20 Galaxies
Authors: Sakhibov F , Smirnov M.A.
Published: June 2019

The simultaneous multiple constraints of the IMF and SFR history based on the observed UBV R colours, Lyman continuum fluxes and chemical abundances Z resolve the IMF-SFR ambiguity in 100 extragalctic star formation complexes in 20 galaxies (SFCs). The separate study of SFCs with different SFR history shows links between IMF parameters and observed properties of SFCs as well as local and global properties of a host galaxy. The SFR history depends on the star density of SFCs. Low density regions demonstrate instantaneous starburst, while in high density SFCs extended star formation bursts are detected. Constrained IMF slopes are in a good agreement with direct observations of IMFs in OB associations of the Milky Way and LMC.
Tidally-induced Super Star Clusters in M82
Authors: Grijs R. de , O'Connell R.W , Gallagher J.S.
Published: June 2019

Using new HST imaging, we identify a large, evolved system of super star clusters in a disk region just outside the starburst core in the prototypical starburst galaxy M82, “M82 B.” This region has been suspected to be a fossil starburst site in which an intense episode of star formation occurred over 100 Myr ago, which is now confirmed by our derived age distribution. It suggests steady, continuing cluster formation at a modest rate at early times (> 2 Gyr ago), followed by a concentrated formation episode ∼ 600 Myr ago and more recent suppression of cluster formation. The peak episode coincides with independent dynamical estimates for the last tidal encounter with M81.
The Top-Heavy Mass Function of the Young Super Star Cluster M82-F
Authors: Smith Linda J. , Gallagher John S.
Published: June 2019

We derive a dynamical mass of 1.2 ± 0.1 × 106 M⊙ for the young SSC M82-F and determine that the current (LV/M)⊙ is a factor of ∼ 5 higher than that predicted by a standard Kroupa (2001) IMF. This suggests that M82-F has a deficit of low mass stars and will not survive to become an old globular cluster.
Stellar Populations in the Antennae (NGC 4038/9): Exploring a Galaxy Merger Pixel By Pixel
Authors: Kassin Susan A. , Frogel Jay A. , Pogge Richard W.
Published: June 2019

We use B, V, and K-band images of the Antennae in a detailed analysis of its stellar populations. Significant large and small-scale spatial variations in the stellar populations are found by examining images pixel by pixel. Flux ratio, or linear color, diagrams allow us to find the stellar populations present in each pixel using a novel technique. This is done through a comparison of the colors of pixels to those of well-studied populations such as elliptical/S0 galaxies, Magellanic Cloud clusters, and Sc galactic nuclei, in addition to stellar population models. This technique allows us to study not only star clusters, but also the diffuse light present in the Antennae. From these flux-ratio diagrams, a luminosity-weighted de-reddened age image of the Antennae is constructed. Our analysis technique complements and extends results based on Hubble Space Telescope images.
Formation of Twin Clusters in a Galactic Tidal Field
Authors: Theis Christian
Published: June 2019

The formation of globular clusters is still an unsolved problem. Though most scenarios assume a massive molecular cloud as the progenitor, it is unclear how the cloud is transformed into a star cluster. Here a scheme of supernova (SN) induced cluster formation is investigated. In this scenario the expanding SN shell accumulates the mass of the cloud. This is accompanied by fragmentation resulting in star formation in the shell. If this stellar shell expands sufficiently slowly, its self-gravity leads to a recollapsing shell, thus forming one or several stellar clusters.

In this paper N-body simulations of collapsing shells moving on circular orbits in a galactic potential are presented. It is shown that typical shells (105 M⊙, 30 pc) evolve to twin clusters in the galactocentric distance range between 3 and 11 kpc. Their masses show a strong radial trend: on orbits inside 5 kpc both clusters have almost equal mass. Outside 5 kpc the more massive twin cluster contains about 55% of the shell's mass, whereas the mass of the smaller decreases linearily to 15% at 11 kpc. Outside 11 kpc the collapsing shells end up in a single cluster. Inside 3 kpc the shells are tidally disrupted and only fragments substantially less massive than the initial shell survive.
Mass Segregation in the Young SMC Cluster NGC 330
Authors: Sirianni Marco , Nota Antonella , De Marchi Guido , Leitherer Claus , Clampin Mark
Published: June 2019

We present a new study of the low end of the stellar IMF of NGC 330, the richest young star cluster in the Small Magellanic Cloud (SMC). Using deep broadband images taken with the HST/WFPC2 we have derived the cluster's luminosity function and constructed the initial mass function (IMF) in the mass range 1 − 7M⊙. We have investigated the IMF as a function of the radial distance from the cluster center. We find that, after correction for background contamination, the IMF is fairly homogeneous with a slope slightly steeper than Salpeter's in the central regions of the cluster (< 40″) but becomes increasingly steeper with distance, indicating a preponderance of massive stars in the core of the cluster. NGC 330 is one of the first clusters for which evidence of mass segregation is directly found.
An HST View of 30 Doradus
Authors: Maíz-Apellániz Jesús , Walborn Nolan R. , H. Barbá Rodolfo
Published: June 2019

We present a five-field, six-color WFPC2 mosaic of 30 Doradus which constitutes the most detailed ever optical image of a starburst region. With the aid of NICMOS, STIS, and CO data we discuss the most recent star formation history in the region and its relationship with the original and present structure of the parent molecular cloud.
The HST Census of Nuclear Star Clusters in Late-type Spirals
Authors: Böker Torsten
Published: June 2019

I describe preliminary results from an I-band snapshot survey with HST/WFPC2 of nuclear star clusters in late-type spiral galaxies. The goal of the program is to derive the fraction of galaxies that harbor a nuclear star cluster, and to analyse their photometric and structural properties. Together with follow-up spectroscopy, the survey will illuminate the formation mechanism of nuclear star clusters and the implications for the dynamical and morphological evolution of the host galaxy.
Circumnuclear Star Formation in Spiral Galaxies from HST Images: NGC 4314
Authors: Winge Cláudia , Pastoriza Miriani G.
Published: June 2019

The first results of a study of the circumnuclear star-forming regions in HST broad band images of the nearby galaxy NGC4314 are presented. After modeling the bulge stellar population using ellipse fitting and subtracting the resulting model from the original images, aperture photometry of the individual star-forming regions in the ring was performed. For a total of 75 regions detected 3σ above the background, we obtained mean colors (f439—f569) = −0.72 ± 0.27, and (f569—f814) = −0.69 ± 0.35, with the NW regions being ∼ 0.5 mag bluer in both colors than the NE ones, an effect that may be caused by internal reddening.
Towards Better Age Estimates for Stellar Populations: The Y2 Isochrones
Authors: Demarque Pierre , Yi Sukyoung , Kim Yong-Cheol
Published: June 2019

New theoretical isochrones are presented and compared to the observational data.
The Determination of the Age of Globular Clusters: A Statistical Approach
Authors: Rengel Miriam , Mateu Juan , Bruzual Gustavo
Published: June 2019

We present a statistical approach for determining the age of Globular Clusters (GCs) that allows estimating the age derived from CMDs more accurately than the conventional method of isochrone fitting. We measure how closely a set of synthetic CMDs constructed from different evolutionary models resemble the observed ones by determining the likelihood using Saha and χ2 statistics. The model which best matches the observational data, of a set of plausible ones, is the one with the highest value of the estimator. We apply this method to a set of three different evolutionary models presented by three different authors. Each of these sets consists again of many different models of various chemical abundances, ages, input physics and the like. We subsequently derive the age of GCs NGC 6397, M92 and M3. With a confidence level of 99%, we find that the best estimate of the age is 14.0 Gyrs within the range of 13.8 to 14.4 Gyrs for NGC 6397, 14.75 Gyrs within the range of 14.50 to 15.40 Gyrs for M92, and 16.0 Gyrs within the range of 15.9 to 16.3 Gyrs for M3.
Building Dwarf Galaxies out of Merged Young Star Clusters
Authors: Fellhauer Michael
Published: June 2019

Young star clusters in interacting galaxies are often found in groups or clusters of star clusters containing up to 100 single clusters. In our project we study the future fate of these clusters of star clusters. We find that the star clusters merge on time scales of a few dynamical crossing times of the super-cluster. The resulting merger object has similarities with observed dwarf ellipticals (dE). Furthermore, if destructive processes like tidal heating, dynamical friction or interaction with disc or bulge of the parent galaxy are taken into account our merger objects may evolve into objects resembling dwarf spheroidal galaxies (dSph), without the need of a high dark matter content.
Modification of the Core Overshoot Treatment
Authors: Woo Jong-Hak , Demaque Pierre , Yi Sukyoung
Published: June 2019

Following Roxburgh's integral constraint, we implemented an upper limit of overshoot in the conventional method of α parameterization in order to remove an overly large overshoot effect for low-mass stars. The erroneously large effect of overshoot due to the failure of α parameterization can be effectively corrected by limiting the amount of overshoot to 15 % of the core radius.
Extragalactic Star Clusters: Speculations on the Future
Authors: Gallagher J. S. , Grebel E. K.
Published: June 2019

We discuss the future possibilities for extragalactic star cluster research with the expected new ground-based and space-based telescopes and instrumentation. Significant gains are expected due to improved angular resolution, sensitivity, and area coverage particularly in the infrared and radio, accompanied by progress in evolutionary and dynamical modelling. Improvements in angular resolution are anticipated, especially through new adaptive optics systems (e.g., Keck, Gemini, VLT), and interferometry (e.g., Keck, VLT, LBT, ALMA, SMA, SkA), and space instrumentation (e.g., Chandra, NGST), enabling studies even of deeply embedded, forming extragalactic star clusters. Tidal disruption of Galactic clusters becomes observable through wide-area surveys such as the SDSS, VISTA, PRIME, including proper motion measurements through high-resolution imaging (e.g., HST, LBT, SIM, GAIA). Sensitive new optical and infrared spectrographs (e.g., HET, SALT, GranTeCan, Magellan, Keck, VLT, CELT, OWL, NGST) will push kinematic and abundance studies to new limits, allowing us detailed comparisons with model predictions. One important wavelength range for the study of young, massive star clusters, the far UV, appears to be neglected by future planned instrumentation.
Conference Summary
Authors: Harris William E.
Published: June 2019

This was a superb conference: scientifically exciting, and wonderfully enjoyable from every viewpoint. The biggest problem was, of course, that trying to absorb all the science has resembled drinking water from a firehose: there has been just too much of it to take in on the spot. So if the purpose of a conference summary talk is to dispense sage advice, then I will say that the best thing all of us can do now is simply to go home and think, and begin digesting this vast array of new material. IAU 207 is sure to be remembered as a launching point for many new directions and syntheses that will emerge from its stimulus over the next several years.
Large Photographic Catalogues
Authors: Röser S. , Nesterov V.V.
Published: June 2019

Large photographic catalogues still have their importance in modern astrometry. Old catalogues are used to derive good-quality proper motions. Present-day catalogues may be used to extend the Hipparcos and Tycho systems to fainter magnitudes.
Tycho Astrometry from 30 Months of Satellite Mission
Authors: Høg E.
Published: June 2019

The Hipparcos satellite's star mapper gives photon counts in two spectral channels simultaneously, close to Johnson B and V. The transit times and the signal amplitudes for each star across two groups of four slits are derived and used for astrometry and photometry, respectively, and this constitutes the Tycho project. The present paper describes results of Tycho astrometric data processing, leading from the transit times to the astrometric parameters of the Tycho stars.

Some 30 months of Tycho observations, i.e. about 80 percent of the Hipparcos-Tycho mission, have been used to produce a working catalogue of Tycho positions, proper motions and parallaxes of a million stars. The external errors of this preliminary catalogue have been determined by comparison of 98 000 stars common with a preliminary, but much more accurate Hipparcos catalogue. External systematic errors of positions and annual proper motions are less than 0.5 milliarcsecond (mas) and the accidental errors per star are about 30 mas rms at V = 10.5 mag, the median magnitude of the catalogue. It is concluded that a satisfactory accuracy has been achieved.
Astrometry with the HST Planetary Camera
Authors: Girard T. M. , Li Y. , Van Altena W. F. , Nunez J. M. , Benedict G. F. , Duncombe R. L. , Hemenway P. D. , Jefferys W. H. , McArthur B. , McCartney J. , Nelan E. , Shelus P. , Story D. , Whipple A. L. , Franz O. G. , Wasserman L. W. , Fredrick L. W.
Published: June 2019

The astrometric capability of the Hubble Space Telescope Planetary Camera (WF/PC1) is investigated, motivated by a study of the internal velocity distribution of globular clusters. The astrometric accuracy of the HST PC will be determined ultimately by 1) the accuracy to which the aberrated images can be ‘centered’, and 2) the accuracy to which the distortions across the PC field can be modeled. A series of overlapping exposures of two clusters, NGC 6752 and M15, are utilized to examine these issues.

We have made use of maximum-likelihood image reconstruction to address the first issue, with good success. Reconstruction improves both the detectability and precision of the image centers. A preliminary exploration of the second issue, that of modeling the distortion across the PC field, is also presented, using positions derived from the multiple overlapping exposures.
High-Precision Astrometry and the Modelling of Stellar Spectra
Authors: Gustafsson Bengt
Published: June 2019

The impact of high-precision astrometry on modelling of stellar spectra and determination of fundamental stellar parameters for single stars is discussed. It is found to be considerable, but improvements in the understanding of stellar atmospheres, and in particular of the physical background of luminosity (i.e., surface-gravity) criteria will be needed in order to match the possibilities of stellar parallaxes with accuracies on the order of a few percents or better.
Sub-Milliarcsecond Optical Astrometry and Binary Stars
Authors: Armstrong J.T.
Published: June 2019

Long-baseline optical interferometry has made it possible to measure the visual orbits of binary stars with major axes as small as 5 mas and errors of ≲ 100 μas. Interferometers now nearing completion will extend these values to ≳ 500 μas and σa ∼ 10 μas. Observations of double-lined spectroscopic binaries with current interferometers have already yielded some mass estimates with precisions rivaling those from fitting the light curves of eclipsing double-lined systems. Luminosity estimates based on combined visual interferometric observations and velocity curves are often more precise than those from more indirect methods based on estimates of Teff. New interferometers now coming into operation will make it possible to measure fundamental parameters in dozens to hundreds of binary systems.
HST in Search of Binaries among Faint Members of the Hyades Cluster
Authors: Franz O. , Kreidl K.J. , Wasserman L.H. , Bradley A.J. , Benedict G.F. , Duncombe R.L. , Hemenway P.D. , Jefferys W.H. , McArthur B. , Nelan E. , Shelus P.J. , Story D. , Whipple A.L. , Fredrick L.W. , Van Altena W.F.
Published: June 2019

The HST Astrometry Science Team is using the Fine Guidance Sensors (FGS) in the Transfer Function (TF) Scan mode to search for binaries among the faint members of the Hyades cluster. To date (March 1994), nine binaries have been discovered among 24 stars examined. The closest pair (total V=13.5) has a separation of 0.051 arcsec; the faintest (sep=0.287 arcsec) has magnitudes V=15.0 and 16.5; neither object posed a challenge to the capabilities of FGS. For another pair, two observations 152 days apart show a 13 deg change in position angle, indicating rapid orbital motion. One decade should suffice to define the orbit with angular dimensions of sub-millisecond of arc accuracy.

Clearly, this work will soon permit mass determinations for low-luminosity members of the Hyades cluster. Moreover, information on the frequency of binaries will provide insight into the role of duplicity in star formation and in the dynamic evolution of the cluster. To be truly useful, a census of binaries in the Hyades (and other clusters) must ultimately reach cluster members fainter than those currently under investigation, requiring astrometry with sub-millisecond of arc accuracy at near-infrared wavelengths.
Detectability of Galactic Kinematical Parameters from Proper Motions
Authors: Smart R.L. , Lattanzi M.G.
Published: June 2019

We discuss the inclusion of a warp structure (as discussed by Miyamoto et al. 1993) to a realistic galactic model. We investigate how the proper motions are effected by changes in the inclination, phase angle and spin velocity of the warp. It is shown that accurate proper motions of disk stars do reflect the variation of warp parameters. A simulation of OB stars with an apparent magnitude limit of 7.0, mimicing the early type content of the HIPPARCOS catalogue, indicates that variations of phase are probably not observable while detection of velocity variation is within the limit of the current precision.
Improvements to Reference Systems and Their Relationships
Authors: Seidelmann P. K.
Published: June 2019

Reference Systems include the reference frames and their relationships, time arguments, ephemerides, and the standard constants and algorithms.

The extragalactic, or radio, reference frame will be the basic frame. Achieving milli to microarcsecond accuracies at optical wavelengths will reduce the disparity between optical, radar, and radio reference frame determinations. Thus, the relationships and identifications of common sources should be much more accurate. Another significant change should be the ability to determine distances, and thus space motions on a three-dimensional basis, rather than the current two-dimensional basis of proper motions.

Improvements in ephemerides provide the opportunity to investigate the difference between atomic and dynamical time, the relationship between the dynamical and extragalactic reference frame and the values of precession and nutation.

Also, the relationships between the bright and faint optical catalogs, the infrared, and extragalactic reference frames should be better determined. Reference frames at other wavelengths will become determinable.
Photometric Facilities of the AIST Space Project
Authors: Kopylov I.M. , Gorshanov D.L. , Chubey M.S.
Published: June 2019

The arguments are given of the choice for the Vilnius seven color medium band photometric system as the most effective one for the AIST space project. A prediction is made of the limiting stellar magnitudes V for every Vilnius passband and the integral band T at σΣ ≤ 30mmag from a 3 year AIST mission.
The Project OSI
Authors: Shao M.
Published: June 2019

The OSI project at JPL is a study of a series of concepts for space based astrometric interferometry. The various concepts are designed for slightly different types of astrometry. The original concept OSI was designed for wide angle/global astrometry by look at stars about 30 degrees apart. A derivative of OSI, called SONATA was designed for narrow angle astrometry (10 arcmin) at sub-microarcsec levels for exo-planet searches. This paper describes optical concepts of theses instruments with regard to metrology and systematic error. In addition to conceptual designs, system error budgets and covariance analysis the OSI project has a technology development program in place to investigate the most difficult problems.

Technology is being persued in three areas. One is laser metrology at the picometer level where sub-picometer accuracy for null metrology has been achieved and < 2 picometer accuracy has been achieved for relative metrology. A second area is the control of vibration on a large space structure. A 5 m truss structure has been built at JPL with an interferometer on the structure to test vibration isolation and control technologies. Tests with this structure will begin in winter of 1994. The key to vibration control for OSI will be the delay lines. The third technology project is a shuttle flight experiment, Stellar Interferometer Technology Experiment (SITE), currently in a phase A study, (part of NASA's INSTEP program). The goal is to fly the experiment on the Shuttle in 1997-1998.
New Measurements of Positions for the Astrographic Catalogue Stars
Authors: Ivanov G.A. , Kislyuk V.S. , Pakulyak L.K. , Sergeev A.V. , Sergeeva T.P. , Yatsenko A.I.
Published: June 2019

Six observatories of the former USSR carry out photographic observations within the FON project (the fourfold coverage of the northern sky) since 1982. The same type wide-angle Zeiss astrographs (D=400 mm, F=2000 and 3000 mm) are used. At present Golosiiv Observatory almost finished the Kiev observational part of the project and the measurements of onefold coverage plates have been started. The special measuring machine PARSEC (Programming Automatic Radial-Scanning Coordinatometer) has recently been constructed for this purpose.

We intend to apply the measurements of the FON project plates to the determination of new positions and proper motions of all stars in the Astrographic Catalogue (AC) using the last one as the first epoch of observations. AC is applied also as input catalogue for PARSEC. About 500 plates have been measured at the moment and proper motions for more than 500000 stars in different areas of the northern sky have been obtained.

The accuracy of the FON positions and proper motions of stars from the measurements of onefold coverage plates is estimated to be 0.35 arcsec and 0.006 arcsec/yr, respectively.

Futher investigations will be carried out in cooperation with Sternberg Astronomical Institute (Moscow, Russia) and Astronomisches Rechen-Institut (Heidelberg, Germany).

The above-described reasearches became possible partly by Grant N V41000 from the International Science Foundation.
A Giant Meridian Circle - Reflector
Authors: Yershov V.N.
Published: June 2019

A 1.5 m reflector is proposed for infrared and optical meridian observations in order to extend the fundamental coordinate system to faintest objects and to the K-infrared waveband. Classical meridian circles are unfit for the infrared observations because their lens objectives do not give good images in the infrared. But reflectors are almost never used as meridian circles due to uncertainties in their optical axis position. The main problem is that the secondary mirror is not connected with the micrometer and the circle reading system. In order to overcome this difficulty the author proposes to use an intermediary focal plane between the primary and the secondary mirrors where a luminous reference grid of wires might be placed. The Gregory optical scheme has such a focal plane, and its secondary mirror forms images of a star and the grid at the micrometer's detecting area. At the same time a special champher around the primary's central hole forms anautocollimated image of the grid near the grid itself. The micrometer measures the star image coordinates relative to two images of the reference grid. So, observations will not be affected by displacements of the secondary mirror and by those of the micrometer. The telescope's equivalent focal length has been chosen as 3 m, and the optical system has been transformed into an aplanatic Mersenne combined with an aplanatic focal reducer corrector (Popov, 1988). A new autocollimated circle reading system is chosen for the instrument (Yershov and Nemiro, 1994). The observations will be linked to the fixed optical axis of two long-focus collimators placed at the prime vertical plane.
An Autocollimation Circle Reading System for the Infrared Meridian Instrument
Authors: Yershov V.N. , Nemiro A.A.
Published: June 2019

A new autocollimation circle reading system is proposed for the reflector meridian circle (Nemiro and Streletsky, 1988). The instrument will be used for observations in the K-infrared waveband. Instead of the divided circle fixed to the instrument tube the new system has small spherical mirrors polished at the lateral surfaces of the primary mirror. The primary mirror is made from sitall and has an autocollimation system aimed at monitoring its optical axis position. The small spherical mirrors of the circle reading system link the circle readings with the primary's optical axis. The divided circles are fixed unmovable opposite to both lateral surfaces of the primary's optical block. Both surfaces have four spherical mirrors. The distance between the divided circles and the mirrors is equal to the mirrors' radii of curvature. The scales of each circle are illuminated from outside (where the measuring microscopes are placed). The mirrors form autocollimated images of the divisions at the plane of the divisions itself. Averaged coordinates of a division and its autocollimated image give the position of the mirror's optical center, and the semi-difference of the coordinates gives the angular position of the telescope. So, the measurements of the circle positions are differential ones, and any displacements of the microscope zero-points are not critical. The precision of measurements is estimated to be better then 0.05″ (random) and 0.005″ (systematical). The work was supported by the Russian Foundation of Fundamental Investigations (the project's code is 93-02-17095).
A Method for Star Image Separation from the Background in Automatic Coordinate Measurements
Authors: Zamarashkin K.N.
Published: June 2019

A method for star image separation from the background is suggested. Applicability of the method is shown on the basis of automatical coordinate measurements of the double star images on astroplates with the use of the “Fantazia-2” Automatic Measuring Complex (AMC) (Kiritchuk et al., 1984). The method provides a minimal dispersion of distances between components of a binary if the statistics of the centre of mass (CM) of discretized image is used for measurements. It have been shown that the CM cannot be considered as an accurate characteristic of the star image position. Nevertheless, the CM showed to be a valuable tool for determination of some local astroclimate parameters (isoplanetic square size). It was assumed that the process of star image formation could be easily checked with the help of the CM statistics if considered level by level in the sense of optical density. Positions of the center of mass of each component in the binary were determined as a function of the threshold and then the cross-correlations between the trajectories were calculated. Strong correlation between images of components of the double star ADS 3353 (angular distance r = 4″) have been discovered, so the components of a binary should not be processed alone in this case. Additional experiments with the double stars ADS 8397 (angular distance between components 14″) and ADS 1090 (20″) have shown that the correlation between the components of the binary became less, but still exists, while the distance is increasing.
RORF - A Radio Optical Reference Frame
Authors: Zacharias N. , Fey A.L. , Russell J.L. , Johnston K.J.
Published: June 2019

The radio observations are based on more than one million pairs of group delay and phase delay rate observations from all applicable dual frequency Mark–III VLBI data from 1979 until the end of 1993.
Near Infrared High Angular Resolution Observations of Stars and Circumstellar Regions by Lunar Occultations
Authors: Chandrasekhar T. , Ashok N. M. , Ragland Sam
Published: June 2019

The high angular resolution technique of lunar occultations enables one dimensional source structure in the direction of occultation to be extracted from the observed fringe pattern after detailed analysis taking into account the frequency response of the detection system, the optical filter bandwidth and the telescope size. A program of observing lunar occultations in the near infrared from 1.2m telescope at Gurushikhar, Mt Abu, India (72°47′E, 24°39′N, 1680m), is currently being pursued. Several occultations have been successfully observed in K band (2.2μm) including a day time event. The instrument used was a InSb based infrared high speed photometer, the details of which are given in a earlier paper (Ashok N.M., Chandrasekhar T. and Sam Ragland, 1994, Experimental Astronomy, 4, 177).
Dynamics of the Alpha Cen System
Authors: Anosova J. , Orlov V.
Published: June 2019

The triple star system αCen AB and Proxima Cen - the component C - is the nearest to the Sun. The study of its dynamics has shown that this system is probable non-chance. The motion of the component C (Proxima) with respect to the centre of mass of the pair AB is hyperbolic with the probability P = 1.0. We observe, therefore, a slow passage of C close to the pair AB. We propose the hypothesis that this system is a part of the stellar moving group. We list the probable members of this group amongst the nearby stars. Amongst them we have the binaries Gliese 140.1 and 676, the triple system ADS 10288 (Gliese 649.1), and the six single stars. The probability to find by chance these stars inside the velocity space cube with the side of 20 km/s around αCen is equal to about 2%.
The High Altitude Observatory White Light Coronagraph Experiment
Authors: MacQueen R. M. , Gosling J. T. , Hildner E. , Munro R. H. , Poland A. I. , Ross C. L.
Published: June 2019

The coronagraph has obtained observations, both by astronaut and ground command, spaced periodically throughout the mission on a time center of approximately six to eight hours. Programs of more frequent operation – to examine short-term temporal variations and transient activity in the corona – have also been run at various times during the mission. The initial coronagraph observations of structures near limb passage experimentally verify that there are several time scales on which visual changes in these structures occur: (a) approximately one-half rotation, presumably accompanying major reorientations of coronal magnetic fields governing large scale coronal structures, (b) hours to days wherein changes to smaller coronal features are due either to structural changes of particular coronal features or to perspective effects and (c) less than hours – during coronal transients – which caused major reorientation of coronal structures by their passage through the coronal medium. Observations of the latter phenomena have provided some of the more spectacular results from the coronagraph (see Figure 1). The particular case illustrated was one stage of a complex series of events associated with activity in region 137, National Oceanic and Atmospheric Administration numbering, near east limb passage on 10 June 1973. The limb exhibited a major system of active prominences extended from the equator to north 25° and produced surges and sprays through the early hours of the day. From approximately 0700 to 0900 UT several Hα and small X-ray flares occurred and 0815 an eruptive prominence was observed by ground-based telescopes to ascend to 1.4 R⊙. This latter event is presumably the source of the transient observed by the coronagraph between 0929 and 1001 by ground command. During this period the material front moved with the apparent projected velocity of 450 km s−1 from 3.6 to 4.8 R⊙, while the arch-like structure expanded to a diameter greater than 2 R⊙. Figure 1 shows the event at 0943 GMT; it is one photograph of the 144 obtained. Within the structure are numerous bright areas and extended structures apparently mapping the distended magnetic field configuration. The general appearance of this transient is indicative of a large magnetic loop, or bottle, expanded outward from the Sun, its leading edge compressed by interaction with the ambient corona. Although there apparently was not a metric radio burst associated with this event, other transients observed later in the mission have associated metric wavelength activity.
Observational Foundations for Assumptions in Cosmology
Authors: Heller Michal , Klimek Zbigniew , Rudnicki Konrad
Published: June 2019

Testing cosmological models is worthwhile as long as the theoretical assumptions, on which these models are based, are true. In this report observational material testing the Cosmological Principle separately for geometry and substratum, is discussed without referring to any given model of the Universe.
Intergalactic Gas
Authors: Field George B.
Published: June 2019

Evidence that rich clusters of galaxies contain hot (T = 108 K) intracluster gas is reviewed. Such gas contributes little to Ω (0.003) but it has been argued that Ω must be less than 0.05 for true intergalactic gas, if accretion of more gas than is observed in rich clusters is to be avoided. This argument is reviewed.

If the de Vaucouleurs' groups are bound by intracluster gas, T is expected to be 105 to 107 K and the contribution to Ω is ≃ 1. Since the clumping factor C is estimated to be ≃ 7, the resulting value of Ω2C is ≃ 7. This does not violate the observed diffuse soft X-ray background intensity. Gas should be sought in such groups. Smoothly distributed gas with 107 < T < 3 × 108 K and Ω = 1 is not ruled out by direct observations.
The Counts of Radio Sources
Authors: Longair M. S.
Published: June 2019

Following the advice of Professor Zel'dovich, I will begin with two platitudes – first, when we consider the implications of the counts of radio sources, we must look at all the counts of radio sources at all frequencies; second, when we attempt to evaluate the implications of the source counts, we should use proper cosmological models and not rely on the local Euclidean model.
Radio Source Counts at Centimetre Wavelengths
Authors: Pauliny-Toth I. I. K. , Kellermann K. I.
Published: June 2019

Counts of radio sources at 5 GHz (6 cm wavelength) have been derived from a number of surveys including a new strong source survey. The source counts do not appear to differ markedly from an integral number-flux relation having a slope of − 1.5 between 5 and 5 × 103 sources per steradian, and show a sharp drop at source densities smaller than 5 sr-1. On the basis of the form of the number counts and the observed anisotropies in the distribution of sources and of their spectra, the cosmological significance of the source counts is questioned. In particular, the evidence for strong cosmic evolution appears weaker than is generally thought unless the cosmological origin of the quasar redshifts is assumed. Measurements of the radio spectra of the sources suggest a dependence of the spectral curvature on flux density.
Isotropization of Homogeneous Cosmological Models
Authors: Novikov I. D.
Published: June 2019

Observations primarily of the microwave background radiation show that the Universe expands isotropically with a high degree of accuracy at the present time and that the matter distribution is homogeneous on a large scale. Thus, the Friedmann cosmological models are a good approximation today for the expanding Universe. This is valid for at least some period of time in the past too. But how did the Universe expand and what was the matter distribution close to the starting point, near the cosmological singularity?
Detection of Gravitational Radiation
Authors: Tyson J. A.
Published: June 2019

The claims by J. Weber must be examined in the context of system time-response and signal-to-noise ratio. After briefly discussing the sources and spectral distribution of system noise, we discuss optimal time-domain filtering. Although five independent groups have searched for two-antenna coincidences, only Weber has claimed any excess at zero time lag. We present preliminary results of a high sensitivity two-antenna coincidence search.