scholarly journals Masers and the Cosmic Distance Scale

1988 ◽  
Vol 129 ◽  
pp. 169-174 ◽  
Author(s):  
Mark J. Reid ◽  
James M. Moran ◽  
Carl R. Gwinn
Keyword(s):  
Sufficient Accuracy ◽  
Distance Scale ◽  
Proper Motions ◽  
Fundamental Parameters ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
Extragalactic Distance Scale ◽  
Maser Sources ◽  
Better Than

Studies of H2O masers have demonstrated the power of VLBI techniques to measure relative positions with sufficient accuracy (∼ 10 μas) to determine proper motions and to estimate distances to maser sources throughout the Galaxy. The distance to four H2O masers have been determined, and the distance to the center of the Galaxy has been determined to be 7.1 ± 1.5 kpc from observations of the H2O masers in Sgr-B2. Proper motion distances for other H2O masers, and possibly for OH masers, may allow the determination of the fundamental parameters describing the size (Ro) and rotation rate (Θo) of the Galaxy with accuracies of better than 10%. Finally, the measurement of the proper motions of H2O masers in nearby galaxies (< 10 Mpc) is feasible and offers the possibility of direct calibration of the extragalactic distance scale.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

scholarly journals Recent improvements to the Cepheid distance scale

1993 ◽  
Vol 139 ◽  
pp. 61-71
Author(s):  
Wendy L. Freedman ◽  
Barry F. Madore
Keyword(s):  
Near Infrared ◽  
Hubble Space Telescope ◽  
Systematic Difference ◽  
Distance Scale ◽  
Nearby Galaxy ◽  
Rr Lyrae ◽  
Cepheid Variables ◽  
Level Of Significance ◽  
Extragalactic Distance Scale ◽  
Better Than

AbstractIn the course of the last decade significant advances have been made in the observations of Cepheid variables and in their successful application to the extragalactic distance scale. Much of this progress has come about as a result of new CCD and near-infrared photometry. These recent improvements are discussed, and a comparison is given of Population I Cepheids and Population II distances. The correspondence is good, with the zero points agreeing at a level of better than 15% in distance. At this same level of significance, a systematic difference between these distances scales may exist, in the sense that the RR Lyrae distances appear to be smaller than the Cepheid distances (if it is assumed, as has generally been done for extragalactic studies of RR Lyraes, that Mv(RR) = 0.77 mag, independent of [Fe/H]). However, several recently-published calibrations of Mv(RR) significantly reduce this discrepancy. Finally, new Cepheid data for the nearby galaxy M81 are presented based on recent Hubble Space Telescope observations.

scholarly journals Orbits of Galactic Globular Clusters from Schmidt Plate Astrometry

1994 ◽  
Vol 161 ◽  
pp. 453-459 ◽  
Author(s):  
M. Odenkirchen ◽  
R.-D. Scholz ◽  
M.J. Irwin
Keyword(s):  
Globular Clusters ◽  
Proper Motions ◽  
Mass Model ◽  
Orbital Parameters ◽  
The Galaxy ◽  
Galactic Globular Clusters

We present results from orbit integrations for the globular clusters M 3 and M 92. Absolute proper motions recently measured from Tautenburg Schmidt plates and a three-component mass model for the Galaxy have been used to derive the galactic orbits of these clusters. Orbital parameters and the influence of observational uncertainties on the determination of the orbits are discussed.

scholarly journals Two Astrometric Projects: LIGHT (Light Interferometer Satellite for the studies of Galactic Halo Tracers) and MIRA (Mitaka/Mauna Kea/Maui Optical and Infra-Red Interferometer Array)

1997 ◽  
Vol 165 ◽  
pp. 561-566
Author(s):  
M. Yoshizawa ◽  
K. Sato ◽  
J. Nishikawa ◽  
T. Fukushima ◽  
M. Miyamoto
Keyword(s):  
Galactic Halo ◽  
Basic Structure ◽  
Proper Motions ◽  
Infra Red ◽  
The Galaxy ◽  
Galactic Astronomy ◽  
Fringe Patterns ◽  
Almost All ◽  
Ccd Arrays ◽  
Better Than

AbstractThe projects LIGHT and MIRA are the space-borne and ground-based optical/Infrared-interferometer projects of the National Astronomical Observatory of Japan. The contents of each project are gradually developing, and the descriptions given below are the preliminary ones studied at the present time.LIGHT (Light Interferometer satellite for the studies of Galactic Halo Tracers) is a scanning astrometric satellite for stellar and galactic astronomy planned to be launched between 2007 and 2010 by a M-V launcher of ISAS, Japan. Two sets of Fizeau-type 40cm-pupil interferometers with 1 m baseline are the basic structure of the satellite optics. The multi-color (U, B, V, R, I, and K) CCD arrays are planned to be used in the focal plane of the interferometer, optimized for detecting the precise locations of fringe patterns. LIGHT is expected to observe the parallaxes and proper motions of nearly a hundred million stars up to 18th visual (15thK-band) magnitude with the precision better than 0.1 milli-arcsecond (about 50 microarcsecond in V-band and 90 micro-arcsecond in K-band) in parallaxes and better than 0.1 milli-arcsecond per year in proper motions, as well as the precise photometric characteristics of the observed stars. Almost all of the giant and supergiant stars belonging to the disk and halo components of our Galaxy within 10 to 15 kpc from the sun will be observed by LIGHT to study the most fundamental structure and evolution of the Galaxy. LIGHT will become a precursor of a more sophisticated future astrometric interferometer satellite like GAIA (Lindegren and Perryman, 1996).

7. The Cepheid Distance Scale and Galactic Kinematic Parameters

1960 ◽  
Vol 10 ◽  
pp. 696-698
Author(s):  
Harold weaver
Keyword(s):  
Primary Source ◽  
Distance Scale ◽  
Proper Motions ◽  
Kinematic Parameters ◽  
Solar Motion ◽  
Cepheid Variables

Cepheid variables have long been a primary source of knowledge of galactic distances. It is therefore important to examine critically the accuracy of the cepheid distance scale to determine whether it is adequate for present needs. Proper motions resulting from the solar motion provide a fundamental determination of the distance scale, according to the well-known formula

Recently Developed Distance Criteria

1983 ◽  
Vol 6 ◽  
pp. 289-300 ◽  
Author(s):  
G. Paturel
Keyword(s):  
Globular Clusters ◽  
Zero Point ◽  
Great Distance ◽  
Distance Scale ◽  
The Earth ◽  
Distant Galaxies ◽  
Preceding Step ◽  
External Galaxies ◽  
Nearby Galaxies

The problem of the determination of distances in astronomy (the so-called problem of the distance scale) is a very old and important problem. About 280 BC Aristarchus of Samos, the famous greek astronomer of the Alexandrian school, already devised a method to find the relative distances to the Sun and Moon in terms of the size of the Earth. Later, Eratosthenes (about 200 BC), another greek astronomer, measured the Earth’s diameter; so the zero-point of this first distance scale was fixed.Now we are interested by extragalactic distances but the same approach is made : (i) determination of relative distances (ii) determination of the zero-point to obtain absolute distances.Some distance criteria can be used to determine the zero-point. These criteria cannot generally be used at a great distance. They permit a comparison between galactic objects, like Cepheids, Novae, Supergiants ..., globular clusters..., and the same counterparts recognized in external galaxies. Often application is limited to nearby galaxies. In a first section we will briefly present this kind of distance criteria. For more distant galaxies other criteria must be employed, the zero-point being here fixed with nearby galaxies whose distances are known from the preceding step. We will discuss these criteria in a second section.

scholarly journals A Complete, Multicolour Survey of Absolute Proper Motions in the Anticentre Direction at Intermediate Latitude: Kinematics of the Galaxy's Stellar Populations

1994 ◽  
Vol 161 ◽  
pp. 447-449
Author(s):  
D.K. Ojha ◽  
O. Bienaymé ◽  
A.C. Robin
Keyword(s):  
Stellar Populations ◽  
Proper Motions ◽  
The Galaxy ◽  
Ubv Photometry ◽  
Better Than

We present the observational results of UBV photometry and absolute proper motions in the anticentre direction at intermediate latitude (l = 167.5°, b = 47.4°) for an 8.6 square degree field. The sample is complete down to V = 17, and the accuracy of the proper motions is better than per century for stars brighter than V = 16. It is attempted here to make an investigation of the structure and kinematics of the Galaxy from absolute proper motions. Details of the present work can be found elsewhere (Ojha et al. 1993).

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