bluuebunny/crossref_metadata_2025 huggingface dataset:
The Very Small Array
Authors: Scott Paul F.
Published: June 2019

The VSA is a 14-element aperture-synthesis telescope for mapping structure in the Cosmic Microwave Background which is now being commissioned at the Teide Observatory, Tenerife. It operates at frequencies between 26 and 36 GHz, with a bandwidth of 1.5GHz. Its elements track the sky, providing fringe-rate discrimination of any instrumental effects such as antenna cross-talk or ground radiation. The instrument incorporates a single-baseline interferometer comprising two large (3.7m) dishes, which is used to provide concurrent (and same frequency) pointed flux measurements of point sources in the VSA fields, the positions of these source having been obtained previously from survey observations made with the Cambridge Ryle Telescope at 15 GHz. The VSA is now completing its commissioning programme and it will start routine observations in September 2000.
Foreground Separation Methods for Satellite and Balloon Experiments
Authors: Belén Barreiro R. , Hobson Michael P. , Lasenby Anthony N. , Vielva Patricio , Martínez-González Enrique , Sanz José L. , Toffolatti Luigi.
Published: June 2019

A combined technique using the maximum-entropy method (MEM) and the mexican hat wavelet (MHW) to separate and reconstruct the physical components of the microwave sky is presented. We apply this method to simulated observations by the ESA Planck satellite in small patches of the sky. The reconstructed maps of the CMB and foregrounds are improved as compared to those obtained with MEM on its own. Moreover, more accurate point source catalogues are produced at each observing frequency. This technique may also be extended to deal with other multifrequency CMB experiments, including all-sky data.
Polarized Microwave Radiation from Dust
Authors: Lazarian A.
Published: June 2019

Observations of cosmic microwave background in the range 10-90 GHz have revealed an anomalous foreground component well correlated with 12 μm, 60 μm and 100 μm emission from interstellar dust. As the recent cross-correlation analysis of WHAM Hα maps with the Tenerife 10 and 15 GHz maps supports an earlier conclusion that the emission does not arise from free-free radiation, the interstellar dust origin of it is left as the only suspect. Two competing models of this emission exist. The more favored at the moment is the spinning dust model, the other is the model that uses grains with strong magnetic response. In the spinning dust model the emission arises from rapid rotation of ultrasmall grains that have dipole moments, while in the other model magnetic grains emit due to thermal vibrations of magnetic dipoles. Both models predict the emission to be partially polarized and this emission can seriously interfere with the CMB polarization measurements. We discuss observational signatures that can be used to distinguish and eventually filter out the polarized component of the microwave dust radiation.
Photometric Properties of Low-Redshift Galaxy Clusters
Authors: Barkhouse W. A. , Yee H. K. C. , López-Cruz O.
Published: June 2019

A recent comprehensive photometric survey of 45 low-z X-ray selected Abell clusters (López-Cruz 1997) has measured significant variations in the faint end slope of the luminosity function (LF). This result indicates that dwarf galaxies (dGs) comprise a different fraction of the cluster population as a function cluster environment. Clusters having a central “cD-like” galaxy have a flatter faint end slope than non-cD clusters. Also, cD clusters were found to have a dwarf-to-giant ratio (D/ G) which was smaller than non-cD clusters. López-Cruz et al. (1997) has suggested that the light contained in cD envelopes can be accounted for by assuming that it is produced from stars that originally formed dGs. In this simple model, the D/ G would be expected to increase with radial distance from the cluster centre due to the decrease in the disruptive forces.
Multifrequency Observations of the S-Z Effect towards A1656
Authors: De Petris M. , Melchiorri F. , Orlando A. , Lamagna L. , D'Alba L. , Rephaeli Y. , Colafrancesco S. , Signore M. , Kreysa E. , Castagnoli C.
Published: June 2019

Observations of the Sunyaev-Zeldovich (S-Z) effect offer the possibility of both investigating evolution of clusters and of determining cosmological parameters when combined with X-ray observations. We describe a dedicated instrument (MITO) consisting of a 2.6-m in diameter telescope operating at 3500 m a.s.l. in the 2.1, 1.4, 1.1 and 0.8 mm channels with ˜ 10% bandwidths. Here we briefly report the results of MITO measurements towards the Coma cluster.
The Study of 12C(α, γ7)16O in massive stars at explosive conditions
Authors: Duorah Kalpana. , Bezbarua Aditi.
Published: June 2019

Massive stars (M ≥ 10M⊙) and supernova are found to be the possible sites for explosive thermonuclear burning. When a massive star collapses, shock waves moving through various convective zones produces explosive situations. The gravitational collapse of a helium exhausted core leads to violent instabilities. The reaction 12C(α, γ)16O is being studied under this condition. Recently it has been found that the coefficients in the semi-empirical mass formula are temperature dependent. Assuming the volume and surface binding to be effective, the nuclear masses, Q values, and reaction rates are calculated. Carbon alpha reaction is found to attain explosive proportion at the high temperature range considered here.
Time Delays in the Gravitational Lens CLASS B1608+656: Results from Second and Third Seasons of VLA Monitoring
Authors: Fassnacht Christopher. , Xanthopoulos Emily. , Rusin David. , Koopmans Leon.
Published: June 2019

The gravitational lens CLASS B1608+656 is one of the most promising lens systems for the measurement of H0 on cosmological scales. The three independent time delays between the four lensed images have been measured, and the extended lensed optical emission holds the promise for a very well-constrained model. The published time delay measurements are based on the first season of VLA monitoring, in which the background source varied by only 5% in flux density. The small level of variation leads to relatively large uncertainties in the determination of the time delays (10-20%). Two more seasons of monitoring have now been completed and the source flux density has changed by ˜25% during that time. We present the results of the continued VLA monitoring and the resulting time-delay analysis. The new data have significantly reduced the uncertainties on the time delays and, hence, reduced the uncertainties on the resulting determination of H0 from this system.
Period-Luminosity-Shape of Light Curve Relation for Cepheids in LMC and SMC
Authors: Ligeza P. , Moskalik P. , Schwarzenberg-Czerny A.
Published: June 2019

In this paper we report our analysis of the period-luminosity-shape of light curve (P-L-S) relation. The data we used came from LMC and SMC Cepheid light curves produced by OGLE-II microlensing survey. We used Principal Components Analysis of covariance matrix of the sets for Cepheids in LMC and SMC separately. Our calibrating set was bounded to long period classical Cepheids pulsating in fundamental mode. The results are used to derive a method for estimation of distances from light curve shape.
Primordial Bubbles within Primordial Bubbles
Authors: Occhionero Franco. , Amendola Luca. , Corasaniti Pier Stefano
Published: June 2019

Two consecutive, distinct episodes of phase transition occurring during inflation may nucleate two generations of bubbles, one inside the other. We design a model of inflation that realizes this sequence and yields bubble spectra that are bimodal and tunable functions of phenomelogical parameters in turn combinations of microphysical parameters. We argue in favor of a tuning of the parameters such that the outer and earlier generation of bubbles becomes hundreds of Mpc/h in diameter (like the local Hubble bubbles of the literature) whereas the inner and later generation becomes tens of Mpc/h in diameter (like the observed large scale voids).
Galactic Foregrounds and CMB Polarization with SPOrt
Authors: Tucci M. , Cortiglioni S. , Carretti E. , Orsini M. , Fabbri R. , Cecchini S. , Sironi G. , Boella G. , Bonometto S. , Gervasi M. , MacCuli C. , Monari J. , Nicastro L. , Orfei A. , Pisani U. , Poppi S. , Tascone R. , Zannoni M.
Published: June 2019

We discuss the expected polarization of the Galactic foregrounds at the SPOrt experiment frequencies 22-90 GHz. We also consider the problem of foreground separation and perform an analysis to estimate their impact on the detection of a cosmological signal.
Results from the Tenerife Experiments
Authors: Watson R. A. , Macias-Perez J. F. , Davies R. D. , Davis R. J. , Wilkinson A. , Rebolo R. , Gutierrez C.
Published: June 2019

The Jodrell-IAC CMB experiments at Teide Observatory, Tenerife consisting of switching radiometers operating at 10, 15 and 33 GHz, and a 33 GHz short baseline interferometer, have covered up to an area of 1 steradian at angular scales from 1° to 10° (l = 20 − 210). Sensitivities of 10μK per beam area have been reached for a combination the most sensitive experiments allowing a measure of the CMB fluctuation amplitude of 30±8μK using mapping techniques which fully exploit the whole data set. Attempts have been made to separate out galactic radio foregrounds and to place limits on a possible spinning dust contribution.
Time variations of water masers
Authors: Liljeström Tarja , Gwinn Carl R.
Published: June 2019

The strong water maser line at 22 GHz is an excellent tool for studying shocked and turbulent interstellar regions, especially, if simultaneous single-dish and VLBI data are available. After a brief review of 22 GHz time variation studies, we focus on effects caused by magnetic field pressure on observed properties of water masers. We use the powerful and rich maser cluster W49N as an example. Furthermore, we point out the connection between postshock wave damping and observed excess in single-dish flux density and line width.
G305.20+0.21: A very young class II methanol maser source
Authors: Walsh Andrew J.
Published: June 2019

Sensitive radio continuum observations of G305.20+0.21 are performed to look for evidence of an ultracompact HII region. None is found at either 8.64 or 4.8GHz above a 5σ detection limit of about 0.25mJy in both cases. Since G305.20+0.21 is such a bright infrared source, there is a large discrepancy between the expected radio flux and the observed upper limits. This is interpreted as evidence that G305.20+0.21 is a massive protostar traced by a methanol maser site.
Mass estimates for the objects related to class II methanol masers with linear position-velocity structure
Authors: Gos'kov Grigorii M. , Sobolev Andrej M.
Published: June 2019

We study the probability density distributions of mass estimates for class II methanol masers with linear position-velocity structure, of maser cluster, using Monte Carlo tecniques. A uniform random distribution of maser sources along an edge-on rotating circumstellar-ring is assumed as a working hypothesis. It is found that in the cases with sufficiently high number (> 6) of observed maser spots it is possible to set upper limits for the mass encircled by the ring. Both turbulent motions and observational uncertainties are shown to result in the broadening of the probability density distribution of the mass estimate. As a consequence, commonly used procedures do not provide correct values for the lower mass estimate. Ten maser objects with the number of observed spots exceeding 6 were chosen for preliminary analysis. Within the framework of the working hypothesis all of these objects were found to be massive (M > 5 M⊙) with negligible probability for the mass exceeding 80 M⊙.
Stellar masers: a review
Authors: Diamond P. J.
Published: June 2019

I review the current state of studies of masers in the circumstellar envelopes of Asymptotic Giant Branch stars.
Highly polarized SiO v = 0 emission from late-type stars
Authors: Shinnaga Hiroko , Tsuboi Masato , Kasuga Takashi
Published: June 2019

We briefly report the results of polarimetric observations of SiO emission from late-type stars taken with a millimeter polarimeter installed at the Nobeyama 45m telescope. We found that the SiO J = 2 − 1 emission in the v = 0 state from R Cas contains a highly linearly polarized component, followed by the detection of highly linearly polarized emission of the same transition from VY CMa (Shinnaga et al. 1999). The high polarization degree is a strong evidence that the v = 0 emission originates from maser action. We found out that, not only a peculiar supergiant star, but also a Mira variable star is associated with the SiO v = 0 maser.
86 GHz SiO masers in late-type galactic bulge stars
Authors: Messineo Maria , Habing Harm , Sjouwerman Loránt , Omont Alain , Menten Karl
Published: June 2019

We present 86 GHz (v = 1, J = 2 → 1) SiO maser line observations with the 30-m IRAM telescope of a small sample of late-type stars in the inner Galaxy. The stars were selected on basis of their infrared magnitudes and colors, and our first results show an instantaneous detection rate of ∼65%. The derived SiO maser fluxes and line-of-sight velocities indicate that the stars are located in the Galactic Bulge. The goals of the project are to study the relation between 86 GHz SiO maser emission and infrared properties of the stars, and to enlarge the number of known stellar line-of-sight velocity measurements. Combining the detections with measurements from other surveys (e.g. OH maser surveys) will allow a kinematic analysis of stellar orbits, and probe the dynamics of the inner Galaxy and its probable triaxial mass distribution.
The dynamics of red supergiant winds
Authors: Richards Anita M. S. , Cohen Raymond J. , Gray Malcolm D. , Murakawa Koji , Yates Jeremy A. , Szymczak Marion , Monnier John D. , Masheder Mike R. W. , van Langevelde Huib J.
Published: June 2019

During the red supergiant (RSG) stage of massive star evolution, emission from dust and molecules allows the copious stellar winds to be studied in great detail. This help us understand not only the evolutionary stages of the star (which are highly dependent on mass loss rates), but also the morphology of the eventual supernova remnant. Maser emission from OH and H2O has been mapped with milli-arcsec resolution (using MERLIN and the EVN/global VLBI) around RSG including VY CMa, S Per and VX Sgr. The H2O masers originate in clouds accelerating away from the star and OH mainlines masers interleave the outer parts of the H2O maser shell. Zeeman splitting of OH maser lines reveals the orientation and strength of stellar-centred magnetic fields.
New detections of 321 GHz water masers toward late-type stars
Authors: Liljeström Tarja , Winnberg Anders , Booth Roy
Published: June 2019

The SEST telescope has been used for a submillimeter water maser survey toward late-type stars. Six new 321 GHz water masers were detected. These, as well as the earlier reported sources, VY CMa and o Cet, were also observed in the vibrationally excited water maser line at 96 GHz. However, only VY CMa and o Cet showed the 96 GHz emission. The line velocity of o Cet is blueshifted, suggesting that the hot water vapor at 96 GHz takes part in the pulsation-shock motion of the Mira variable.
The ATCA/VLA OH 1612 MHz survey: identification of post-AGB stars
Authors: Chapman Jessica , Sevenster Maartje
Published: June 2019

The ATCA/VLA Galactic Plane survey detected OH 1612 MHz maser emission from a total of 766 sources. In most cases the detected sources have double-peaked spectral profiles which are characteristic of OH/IR stars. A small number of sources however have irregular spectra and uncertain classifications. We discuss the maser results for two sources with irregular OH spectra, D046 (OH 326.5-0.4) and B292 (OH009.1-0.4). For B292 we detected OH 1720 MHz emission - a transition previously unknown for evolved stars. D046 has exceptionally broad maser profiles and strong non-thermal radio continuum emission. Both are likely to be bipolar post-AGB sources.

Post-AGB sources can be identified from their MSX far-infrared properties. For the ATCA/VLA OH-selected sample, most of the likely post-AGB stars do not have unusual OH 1612 MHz spectra.
Detection of an inner torus in the protoplanetary nebulae OH231.8+4.2
Authors: Desmurs Jean-François , Sánchez Contreras C. , Bujarrabal Valentín , Colomer Francisco , Alcolea Javier
Published: June 2019

We performed the first VLBI observations of the SiO v = 1 and v = 2 J = 1-0 masers in a Proto Planetary Nebula OH 231.8+4.2 (also known as the Rotten Egg nebula), at milliarcsecond resolution. Only the v=2 maser transition was detected. We detect several maser spots lying along a line which is almost perpendicular to the axis of symmetry of the Nebula. We find that all the emission is concentrated in an area of ∼ 10 mas, indicating that the SiO masers are originated very close to the surface of the star. One of the two emission areas presents an elongated structure with a clear velocity gradient. The detected emission is consistent with a torus, or disk, in rotation with a velocity of ∼ 6 km/s and with an infall velocity of ∼ 10 km/s.
Zeeman splitting of OH masers and the galactic magnetic field
Authors: Fish Vincent L. , Reid Mark J. , Argon Alice L. , Menten Karl M.
Published: June 2019

Zeeman measurements of OH masers are used to probe the magnetic field around regions of massive star formation. Previous observations suggested that OH maser field directions were aligned in a clockwise sense in the Milky Way, but recent data from a large-scale VLA survey do not support this hypothesis. However, these observations suggest that the magnetic field of the Milky Way is correlated on kiloparsec scales.
OH inversions in star-forming regions and ALI radiation transfer
Authors: Gray Malcolm D.
Published: June 2019

I introduce a new model of OH maser pumping in star-forming regions, based on exact radiation transfer models of the interface between an expanding ucHII region and undisturbed molecular material. The model incorporates the most recent set of rate-coefficients for collisions of OH with molecular hydrogen, and an improved model of continuum emission from dust. FIR line overlap is incorporated into the model in a manner which avoids the inconsistencies associated with the Sobolev approximation.
The Formation Chronology of Local Group Spiral Galaxies
Authors: Sarajedini Ata
Published: June 2019

The ‘Second Parameter Effect’ (2ndPE) has long been recognized as an important probe into the formation of spiral galaxies. The concept that the horizontal branch morphologies of globular clusters are primarily affected by metal abundance in the inner halo (RGC<8 kpc) of the Galaxy but require an additional parameter (probably cluster age) to explain their behavior in the outer halo (RGC > 8 kpc), suggests that the former experienced a rapid monotonic collapse while the latter underwent a slower chaotic formation scenario. As such, in the Milky Way, the so-called second parameter boundary is located at 8 kpc. We find that, in the other Local Group spirals — M31 and M33 — this boundary lies at ∼40 kpc and ∼0 kpc, respectively. We therefore speculate that the boundary delimiting rapid monotonic halo collapse from the chaotic accretion of dwarf galaxy fragments is inversely related to the mass of the spiral galaxy.
A Space Motion Study of the Globular Cluster M13
Authors: Chen L. , Wang J.J. , Zhao J.L.
Published: June 2019

Positions and absolute proper motions of 264 stars in the field of about 70′ × 70′ around the globular cluster M13 were determined. In the astrometric reduction, three early and three late epoch plates taken with the 40cm refractor at Shensan, Shanghai, China, were used, with the time baseline of 73 years. The reduction was done using the central overlapping algorithm, with 5 Hipparcos stars and 38 Tycho-2 stars used as reference stars. Based on the reduced proper motion data, the membership probabilities of the sample stars were determined. An absolute proper motion of the cluster of 1.49 ± 0.36 mas yr−1 in right ascension and 3.06±0.35 mas yr−1 in declination was obtained. From this proper motion, together with distance and radial velocity data, we derived the space motion of M13 and via numerical integration also the orbit of the cluster in the Galaxy.
Comparative Classification of Globular Clusters in the Galaxy and LMC
Authors: Yatsyk Olga , Eigenson Olexij
Published: June 2019

The distributions of 141 globular clusters in the Galaxy and 54 globular clusters in the LMC in space with coordinates being their dynamical parameters are considered by taxonomical analysis. The majority of clusters are shown to enter several taxons (classes) with narrow enough limits of these parameters. Classes are not isolated and continually transfer between each other. It possibly means an absence of significant gaps in clusters' formation process. Taxonomical analysis of the joint distribution for both samples showed that though LMC clusters essentially differ in color and mass in the space of their dynamical parameters some part of them are similar to Galaxy globular clusters.
A Large and Homogeneous Sample of CMDs of LMC Stellar Clusters
Authors: Brocato Enzo , Di Carlo Elisa
Published: June 2019

We present the photometric results of 21 stellar clusters of the Large Magellanic Cloud. The WFPC2 images were retrieved from the HST archive. Simple stellar populations in a large spread of age are well represented in the sample of color-magnitude diagrams shown here.
Old LMC Globular Clusters: Reticulum
Authors: Marconi Gianni , Ripepi Vincenzo , Andreuzzi Gloria , Bono Giuseppe , Buonanno Roberto , Cassisi Santi
Published: June 2019

We present a preliminary analysis of homogeneous, deep and accurate multiwavelength U, B, V, and I data of the old LMC cluster Reticulum. The comparison between theory and observations seems to suggest that the reddening toward this cluster is a factor of 2 larger than suggested in the literature. Both cluster distance and age are in agreement with the canonical values. Finally, the main goals of this project are briefly discussed.
Discovery of Likely Globular Clusters in Maffei 1
Authors: Buta R. , McCall M. L.
Published: June 2019

The Hubble Space Telescope Wide Field and Planetary Camera 2 was used to image at high resolution the core region of the nearby, heavily obscured massive elliptical galaxy Maffei 1. We report on the discovery of 19 diffuse objects in the WFPC2 field that are likely to be globular clusters associated with Maffei 1. We present some preliminary data on the luminosities, colors, and sizes of these candidates.
The Globular Cluster System of NGC 5128
Authors: Rejkuba Marina
Published: June 2019

On the basis of high resolution ground-based images, taken with VLT and FORS1, 71 bona fide globular clusters were discovered in the halo of NGC 5128. Only 5 of these clusters were previously known. In a UV color-magnitude diagram for the complete sample of 71 clusters and a (U—V)0vs. (V—Ks)0 color-color diagram for a subsample of 23 clusters, the objects span a similar magnitude and color range as the globular clusters in the MW and M31. The GCLFs spanning −10.1 < MV < −4.9 and −9.3 < MU < −3.3 have been constructed. These are the deepest GCLFs of in a gE made so far. The Kolmogorov-Smirnov statistics show that GCLF of the giant elliptical NGC 5128 is consistent with the ones of spiral galaxies like the MW and M31.
The Globular Cluster System of NGC 1316
Authors: Gómez Matías , Richtler Tom , Infante Leopoldo , Drenkhahn Georg
Published: June 2019

We have studied the Globular Cluster System of the merger galaxy NGC 1316 in Fornax, using CCD BV I photometry. Dividing the sample into red (presumably metal-rich) and blue (metal-poor) subpopulations at B - I = 1.75, we find that they follow strikingly different angular distributions. The red clusters show a strong correlation with the galaxy elongation, but the blue ones are circularly distributed. An astonishingly low specific frequency for NGC 1316 of only SN = 0.9±0.2 is derived, which confirms with a larger field a previous finding by Grillmair et al. (1999). Assuming a “normal” SN of ∼ 4 for early-type galaxies, we use stellar population synthesis models to estimate the merger age to about 2 Gyr, if an intermediate-age population were to explain the low SN we observe. By fitting t5 functions to the Globular Cluster Luminosity Function (GCLF), we derive the following turnover magnitudes: and . They support that NGC 1316, in spite of its outlying location, is at the same distance as the core of the Fornax cluster.
A Comparative Study of Globular Cluster Systems in UGC 9799 and NGC 1129
Authors: Gyoon Lee Myung , Kim Eunhyeuk , Geisler Doug , Bridges Terry , Ashman Keith
Published: June 2019

We present a preliminary analysis of HST-WFPC2 observations of globular cluster systems in the two brightest galaxies, UGC 9799 (cD) and NGC 1129 (non-cD), located in the center of rich clusters.
Systematic Properties of Young Clusters and Associations in Galaxies
Authors: Kennicutt Robert C. , Bresolin Fabio , E. Dolphin Andrew
Published: June 2019

We review what is known about the large-scale trends in the sizes, luminosities, and mass functions of young stellar associations and clusters in nearby galaxies. We also describe an ongoing survey of massive young cluster populations in nearby galaxies.
Giant Molecular Clouds and Cluster Formation
Authors: Rubio Mónica
Published: June 2019

We will review the present knowledge of molecular cloud properties and its relation to star formation. We will discuss the evidence for cluster formation associated with giant molecular clouds, and will concentrate on recent results in our Galaxy and the Magellanic Clouds.
Variable Stars in Clusters and the Distance Scale - Some Recent Results Concerning the LMC Cluster NGC 1866
Authors: Walker Alistair R. , Raimondo Gabriella , di Carlo Elisa
Published: June 2019

After summarizing the importance of clusters and variable stars in the context of the distance scale, we focus on two new, and independent, programs to determine the distance to the Large Magellanic Cloud cluster NGC 1866.
Mass Determinations of Star Clusters
Authors: Meylan Georges
Published: June 2019

Mass determinations are difficult to obtain and still frequently characterised by deceptively large uncertainties. We review below the various mass estimators used for star clusters of all ages and luminosities. We highlight a few recent results related to (i) very massive old star clusters, (ii) the differences and similarities between star clusters and cores of dwarf elliptical galaxies, and (iii) the possible strong biases on mass determination induced by tidal effects.
Dynamical Friction in dE Globular Cluster Systems
Authors: M. Lotz Jennifer , W. Miller Bryan , C. Ferguson Henry , Stiavelli Massimo , Telford Rosemary
Published: June 2019

The dynamical friction timescale for globular clusters to sink to the center of a dwarf elliptical galaxy (dE) is significantly less than a Hubble time if the halos have isothermal profiles and the globular clusters formed with the same radial density profile as the underlying stellar population. We examine the summed radial distribution of the entire globular cluster systems and the bright globular cluster candidates in 65 Virgo and Fornax Cluster dEs for evidence of dynamical friction processes. We find that the bright dE nuclei could have been formed from the merger of orbitally decayed massive clusters, but the faint nuclei are several magnitudes fainter than expected. These faint nuclei are found primarily in MV > −14 dEs which have high globular cluster specific frequencies and extended globular cluster systems. In these galaxies, the formation of new star clusters, high central dark matter densities, extended dark matter halos, or tidal interactions may act to prevent dynamical friction from collapsing the entire globular cluster population into a bright nucleus.
Predicting Metallicities and Color Distributions for Secondary GCs Forming in Spiral Galaxy Mergers at Various Redshifts
Authors: v. Alvensleben Uta Fritze
Published: June 2019

In a 1st step I present results from our new set of evolutionary synthesis models for Simple (= single burst) Stellar Populations (SSPs) of various metallicities, and in a 2nd step I combine these results with the information we have about the redshift evolution of spiral galaxies’ ISM abundances. The aim is to provide a grid of color and luminosity distributions of any secondary GC population formed at some time in the past in those mergers for comparison with observations.
The Size Distribution of Massive Young Clusters
Authors: Maíz-Apellániz Jesús
Published: June 2019

We have searched the WFPC2/HST archive for data on nearby massive young clusters with low extinction and we have analyzed 27 such objects. A clear dichotomy between objects with a compact core and without it is observed. We attribute this bimodality to the initial conditions of the parent giant molecular clouds and we discuss its implication towards the long-term evolution of the clusters.
Template Integrated Spectra of Star Clusters
Authors: Santos João F. C. , Alloin Danielle , Bica Eduardo , Bonatto Charles J.
Published: June 2019

We present a set of star cluster integrated spectra based on observations from the ultraviolet to the near-infrared. Mean template spectra were built following a ranking of clusters according to age and metallicity, which were taken from recent studies and put on consistent scales. The complete spectral database including star clusters, galaxies and stars (templates and individuals) is available through the CDS.
Relative Astrometry with Imaging Transit Telescopes
Authors: Benedict G. F. , McGraw J. T. , Hess T. R.
Published: June 2019

A CCD/Transit Instrument (CTI) has produced relative astrometry with standard errors less than 2.6% of a 1.55 arcsecond pixel for stars with V ≤ 17. Additional astrometric studies with existing data are required to better understand the ultimate contribution these devices can make to our science.

The CTI is presently dismantled, awaiting a move to a new site. We briefly discuss the potential astrometric scientific returns from the exisiting data set, from a refurbished CTI, and from a similar device emplaced on the Moon.
Double Star Astrometry with the Hipparcos Data
Authors: Mignard F.
Published: June 2019

As we approach the final processing of the observations carried out by HIPPARCOS, in particular for the double and multiple stars, it is possible to provide reliable statistics on the number of such objects detected and on the quality of the relative and absolute astrometry and photometry. About 24 000 stars have been recognized as non-single, including 11 000 already known as double and multiple before the mission and 13000 discovered by Hipparcos. Also, a subset of 16 000 stars among the 24 000 have been successfully solved for their relative coordinates (position angle and separation) with an accuracy in the range of 3 to 30 mas, including 7000 new double stars. I outline in this paper the principle of the internal recognition procedure and present some statistics on the solution.
Astrometric and Astrophysical Insights into the Hipparcos Data Quality
Authors: Perryman M.A.C.
Published: June 2019

Internal error estimates and external verifications indicate that median errors for the 120000 stars in the Hipparcos Catalogue, for each of the five astrometric parameters, will be in the range 1–1.5 mas. This paper illustrates some of the statistical investigations that have been conducted so far, including comparisons with catalogues of ground-based positions and proper motions, the structure of the Hertzsprung-Russell diagram, results of the reanalysis of meridian circle and photographic plate data using the positions determined from the satellite, and expected results on double and multiple stars and photometric variability.
Binary Star Astrometry with the Hubble Space Telescope: One Millisecond of ARC Accuracy and Beyond
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

We briefly review the concept of double star measurement with HST Fine Guidance Sensors (FGS) in the Transfer Function (TF) Scan mode and give results for three calibration binaries observed with FGS3. Agreement among multiple observations indicates an astrometric precision of 1 millisecond of arc (mas) per observation. We compare measured angular separations with ephemeris values from orbits based entirely on speckle observations. This comparison shows that the accuracy of binary-star astrometry with FGS3 in the TF-Scan mode is 1 mas per observation. Multiple observations can be expected to produce relative positions of binary components at sub-millisecond of arc accuracy.
High-Precision Timing of Millisecond Pulsars and Precision Astrometry
Authors: Kaspi V. M.
Published: June 2019

We present the technique of long-term, high-precision timing of millisecond pulsars as applied to precision astrometry. We provide a tutorial on pulsars and pulsar timing, as well as up-to-date results of long-term timing observations of two millisecond pulsars, PSRs B1855+09 and B1937+21. We consider the feasibility of tying the extragalactic and optical reference frames to that defined by solar system objects, and we conclude that precision astrometry from millisecond pulsar timing has a bright future.
Late Stages of Stellar Evolution
Authors: Thejll P.
Published: June 2019

A review is given of the use of high-accuracy astrometry on research on white dwarfs and the hot subdwarfs and central stars of planetary nebulae (CSPN). Predictions are made about the expected impact of HIPPARCOS, and the possible impacts of GAIA and ROEMER. Discovery of large numbers of new white dwarfs is expected, and, for the more distant hot subdwarfs and CSPN, important refinements of our current understanding of these objects. For white dwarfs independent values of mass and radius may be accurate enough to allow new understanding of the internal composition.
Sub–Milliarcsecond Astrometry of Star Clusters and Associations
Authors: Van Leeuwen Floor
Published: June 2019

Some of the possibilities created by sub–milliarcsecond astrometry in the study of both nearby and distant star clusters are presented.
Galactic Dynamics and Dark Matter with Sub-Milliarcsecond Astrometry
Authors: Pfenniger D.
Published: June 2019

Improving the astrometric accuracy by one or two orders of magnitude over ground-based techniques will not only change our raw knowledge about the Galaxy, but it will also modify 1) the fundamental questions that can be addressed, and 2) the stellar dynamical concepts used so far. More detail in Galactic structure, such as the shape and flow in its putative bar, will be accessible. Also, with the instruments of the next generation the large scale dark matter distribution in the Galaxy, whether distributed in a spheroidal smooth halo or a massive outer disc made of cold clumpy gas, will be measurable. Techniques used for mapping the cosmic flow and mass distribution at Mpc scales and more might be applied to the solar neighbourhood to find the degree of clumpiness of the local matter distribution.
Motions of Globular Clusters
Authors: Brosche P. , Odenkirchen M. , Tucholke H.-J , Geffert M.
Published: June 2019

Absolute proper motions of seven globular clusters have been determined with respect to extragalactic references and with accuracies of ∼ 1 mas/yr. Derived quantities and qualitative implications are described.
The Kinematics of the Magellanic Clouds
Authors: Westerlund B.E.
Published: June 2019

It is essential for our understanding of the evolution of the Magellanic System, comprising the Large and the Small Magellanic Cloud, the Intercloud or Bridge region and the Magellanic Stream, to know its motions in the past. The Clouds have a common envelope of neutral hydrogen; this indicates that they have been bound to each others for a long time. The Magellanic System moves in the gravitational potential of our Galaxy; it is exposed to ram pressure through its movement in the galactic halo. Both effects ought to be noticeable in their present structure and kinematics. It is generally assumed, but not definitely proven, that the Clouds have been bound to our Galaxy for at least the last 7 Gyr. Most models assume that the Clouds lead the Magellanic Stream. The interaction between the Clouds has influenced their structure and kinematics severely. The effects should be possible to trace in the motions of their stellar and gaseous components as pronounced disturbances. Recent astrometric contributions in this field show a great promise for the future if still higher accuracy can be achieved.
Earth Orientation - The Current and Future Situation
Authors: McCarthy Dennis D.
Published: June 2019

Sub-milliarcsecond astrometry often requires an accurate characterization of the orientation of the Earth in a quasi-inertial reference frame. The International Earth Rotation Service (IERS) standards provide the current state of the art in the transformation between celestial and terrestrial reference systems. Improvements in the determination of Earth orientation parameters which describe this transformation continue to be made. Current and future capabilities are given.
On the Registration System of the AIST-Project
Authors: Chubey M.S. , Pashkov V.S. , Kopylov I.M. , Kirian T.R. , Nickiforov V.V. , Markelov S.V. , Ryadchenko V.P.
Published: June 2019

The researches on the AIST-project are directed to the design of the focal plane assembly. The concept of the chip-mosaic and numeric simulation of the two-pixels mode of the signal sampling are presented.
Possibilities of Sub-Milliarcsecond Astrometry in the LOMONOSOV Project
Authors: Cherepashchuk A.M. , Nesterov V.V. , Sheffer E.K.
Published: June 2019

Scientific and technical problems of accuracy improvement of stellar position measurements in the LOMONOSOV project are discussed. In contrast to the HIPPARCOS project, in our project we use a steerable satellite with a three-axis spatial stabilization. A Cassegrain-type 1-meter mirror telescope will be mounted on board of the satellite. We discuss scientific goals in astrophysics, stellar astronomy and astrometry, for which the knowledge of stellar positions with sub-milliarcsecond accuracy is necessary.
Progress Report on the Southern Proper Motion Program
Authors: Platais I. , Girard T. M. , Kozhurina-Platais V. , Mendez R. A. , Van Altena W. F. , Lopez C. E. , Ma W. Z.
Published: June 2019

We present the status of the Yale/San Juan Southern Proper Motion program (SPM) which is the southern hemisphere extension of the Lick Observatory Northern Proper Motion program with respect to faint galaxies (Platais et al., 1993). To date, measurements and reductions in the South Galactic Pole region comprising ≈ 1000 square-degrees on the sky have been finished. At this stage of the SPM program particular attention has been paid to the plate model choice along with an assessment of and accounting for systematic errors. For our establishing of a secondary reference frame we have noticed the presence of a potentially dangerous effect, so–called field–independent coma which is caused by lens decentering. We acknowledge the superb Hipparcos preliminary positions without which such analysis would be virtually impossible. The SPM data at the SGP region have also been used to constrain a multi–component Galaxy model. First results of this analysis are presented.
Stellar Diameter Measurements with Fiber Optic Double Fourier Interferometry—Experimental Study
Authors: Zhao Peiqian , Du Foresto V. Coudé , Mariotti J.-M. , Lena P. , Zhou Bifang
Published: June 2019

Long baseline optical interferometry has been successfully employed to measure the diameters of stars. In this technique, bandwidth smearing can affect the measurement accuracy. These bandwidth smearing effects can be, to some extent, eliminated by dividing the whole observing spectral band into sub-bands and calculating the star's diameter based on the visibilities and spatial frequencies at the corresponding sub-bands. In the visible range, dividing the whole spectral band can be implemented by introducing a spectrograph, while in the IR domain, this operation can be performed efficiently with the technique of double Fourier interferometry (DFI) without losing the advantage of multiplexing. In particular, the use of IR single-mode fiber optics for DFI will make the interferometer extremely compact, light, insensitive to surrounding conditions, etc. We established an IR single-mode fiber optic double Fourier interferometer in the laboratory, in which the optical path difference modulations are generated by stretching fiber arms and the beam combination is carried out with a fiber optic directional coupler. In this paper, we report on experiments and experimental results from measurements of the diameter of an artificial star with the technique of fiber optic DFI.
Stellar Image Location with Maximum Correlation Procedure
Authors: Zi Zhu
Published: June 2019

The location method and accuracy analysis has become a very important subject in astrometry since the photoelectric technique was widely applied. The location methods of the stellar images observed with the slit micrometer are discussed in this paper, and a new estimation method called the maximum correlation procedure is presented. This procedure has already been used to process and analyze the observational data. Because of the ideal mathematical performance of the correlation function, the procedure provides us a good way to determine image locations. By means of simulated observations according to the theoretical analysis, we find that the locating accuracy and the limiting magnitude for this method is much higher than those of traditional locating method. For the observational data of about one thousand stars obtained with the Photoelectric Astrolabe at Yunnan Astronomical Observatory, the positional accuracy of a single star using the maximum correlation is improved by 0.045 arcsec over that with the median. The maximum correlation procedure has also increased the data reduction ability for faint star observations with very low signal to noise ratios.
Potential of MCP Based Photodetecting Systems for High Accuracy Astronomical Object's Observation
Authors: Rodionov I.D. , Knizhnikov M. Yu. , Solomatin E.B.
Published: June 2019

An ideal receiver of radiation should record the arrival time and coordinates of each incoming photon. Available CCD arrays (accumulation mode) and microchannel plate detectors (photon counting mode) are mere approximations to the ideal configuration.
Precision vs. Accuracy in Star Catalogs
Authors: Taff L. G. , Morrison J. E. , Smart R. L.
Published: June 2019

As better precision is achieved and more sophisticated reduction methods are created previously invisible biases surface. This has been especially true in astrometric Schmidt plate work. The problem of their amelioration is not fully solved and precision per se is meaningless in the presence of poor accuracy of comparable amplitude. Continuing to benignly neglect this issue puts us in the position of standing on only one statistical leg. New techniques have been designed to further minimize systematic errors. Of especial interest to star catalog analysis is the method of infinitely overlapping circles (Taff, Bucciarelli & Lattanzi, ApJ 361, 667, 1990; Taff, Bucciarelli & Lattanzi, ApJ 392, 746 1992; Bucciarelli, Taff & Lattanzi, J. Stat. Comp. and Sim. 48, 29 1993). With it almost complete success has occurred with regard to the removal of systematic errors which creep into compilation catalogs as a result of inadequate treatment of catalog-to-catalog systematic errors; they can essentially be eliminated a priori or a posteriori (Bucciarelli, Lattanzi & Taff, in press in ApJ 1994; Taff & Bucciarelli, in press in ApJ 1994). What infinitely overlapping circles does can be briefly described as follows: Let X (x) be the measured (true) value of a standard coordinate, S(x,y) (ε) be the systematic (random) error in x at this point, let w∞ be the infinitely overlapping circle weight, a be the standard deviation of the random error in x, N be the total number of stars in this circle which has radius R, and x0,y0 be the coordinates of the center of this circle.
A Test of the Astrometric Quality of the Southern Guide Star Catalog 1.2
Authors: Bucciarelli B. , Sturch C. R. , Lasker B. M. , Lattanzi M. G. , Girard T. M. , Platais I. , Van Altena W. F.
Published: June 2019

We used preliminary positions of the Yale Southern Proper Motion (SPM) catalogue (Platais, Girard et al., Astronomy from Large Database II, eds. Heck & Murtag, 1992) in a region of 5 fields around the South Galactic Pole to assess the astrometric accuracy of the mask solution (Taff, Lattanzi and Bucciarelli, ApJ 361, 667, 1990), which will be used (in combination with the subplate method) for the construction of the Guide Star Catalogue (GSC) version 1.2. Another semi-external check is done by direct comparison of GSC positions of stars lying onto overlapping plate areas. Results in tables 1 and 2 show that the average rms of the GSC–SPM differences is quite satisfactory (∼ 0.33 arcsecper coordinate), while an error degradation (up to ∼ 1 arcsecpositional) can occurr within a limited area at the plate corners, its signature varying from plate to plate. This can be cured on a plate-by-plate basis by the use of a filtering technique, e.g., as provided by the Collocation method (Bucciarelli, Lattanzi and Taff, ApJ Suppl. 84, 91, 1993), wherever a suitable reference star density is available.
Random Errors of Tycho Astrometry
Authors: Makarov V.V. , Høg E.
Published: June 2019

The paper focuses on the problem of estimation of Tycho astrometry random errors, caused by photon noise. A theoretical model for the random errors was developed on the basis of the Maximum Likelihood estimator. The model provides a satisfactory agreement with experimental data in the wide range of star magnitudes from 4 to 10 for both vertical and inclined slit transits. It is confirmed theoretically, that for fainter stars, which constitute a half of the Tycho star sample, this model is not valid. Moreover, it is demonstrated that a reliable astrometry could hardly be achieved for these faint stars, were it not for a kind of Bayesian approach which is in fact implemented in the processing. This approach uses implicitly a priori astrometric information on positions of the stars. A major drawback of the method is that it introduces some bias in astrometry estimation, of presently unknown size. Nonetheless, no transfer of systematic errors from the input catalogue is expected, for the used prior information comes from Recognition, hence it is based purely on the satellite's own observations. – The inadequacy of the pure ML theory leads us to correct the model empirically, in order to provide reliable formal errors for the astrometric parameters in the final catalogue, for all Tycho magnitudes. In this way, a rms normalized residual is used for each star individually as a scale factor or correction to the formal covariances. Corrected in this way, formal errors are compared directly with external errors, calculated from absolute differences between the Tycho provisional parallaxes in a 30 months solution and the Hipparcos parallaxes of some 100 000 common stars. Analysis of a standard external error shows that the corrected formal errors are robust, and probably even overestimated.
A Compiled Catalog of Optical Positions of Extragalactic Radio Sources
Authors: Jin W. J. , Li J. L. , Xu T. Q. , Wang S. H.
Published: June 2019

Based on 27 individual catalogues, which have been published since 60s' and consist of the positions of the counterparts of extragalatic radio sources, we have compiled a combined catalogue by means of Aoki (Aoki, S. et al. 1983) method for transferring the reference frame from FK4 to FK5 and the referred epoch from B1950.0 to J2000.0 and IERS method (Feissel, M. et al. 1988), which is used for compiling the combined catalog of radio sources. Of course, in the compiling procedure the systematic differences of Peth 70, AGK3RN, and AGK3 (Schwan, H. 1985) have been considered.