Determination of galactic rotation parameters and the solar galactocentric distance R 0 from 73 masers

The major stumbling block in the determination of a rotation curve beyond the solar circle has been the lack of a suitable set of objects with well defined and independently measured distances and velocities which can be observed to large galactocentric radii. Two things have changed this situation. The first was the realization that essentially all local HII regions have associated molecular material. The second was the acquisition of reliable distances to the stars exciting a sizable number of HII regions at large galactocentric radii (Moffat, FitzGerald, and Jackson 1979). Because the velocity of the associated molecular gas can be measured very accurately by means of radio observations of CO, we have been able to overcome the past difficulties and have measured the rotation curve of the Galaxy to a galactocentric distance of 18 kpc.

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Calibrating the BHB star distance scale and the halo kinematic distance to the Galactic Centre

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2819 ◽

2020 ◽

Vol 499 (1) ◽

pp. 1058-1071

Author(s):

Nikita D Utkin ◽

Andrei K Dambis

Keyword(s):

Velocity Dispersion ◽

Anisotropy Parameter ◽

Galactic Centre ◽

Galactic Rotation ◽

Galactocentric Distance ◽

Absolute Value ◽

Dispersion Tensor ◽

Rr Lyrae ◽

Parameter Values

ABSTRACT We report the first determination of the distance to the Galactic Centre based on the kinematics of halo objects. We apply the statistical-parallax technique to the sample of ∼2500 blue horizontal branch (BHB) stars compiled by Xue et al. to simultaneously constrain the correction factor to the photometric distances of BHB stars as reported by those authors and the distance to the Galactic Centre to find R = 8.2 ± 0.6 kpc. We also find that the average velocity of our BHB star sample in the direction of Galactic rotation, V0 = −240 ± 4 km s−1, is greater by about 20 km s−1 in absolute value than the corresponding velocity for halo RR Lyrae type stars (V0 = −222 ± 4 km s−1) in the Galactocentric distance interval from 6 to 18 kpc, whereas the total (σV) and radial (σr) velocity dispersion of the BHB sample are smaller by about 40–45 km s−1 than the corresponding parameters of the velocity dispersion ellipsoid of halo RR Lyrae type variables. The velocity dispersion tensor of halo BHB stars proved to be markedly less anisotropic than the corresponding tensor for RR Lyrae type variables: the corresponding anisotropy parameter values are equal to βBHB = 0.51 ± 0.02 and βRR = 0.71 ± 0.03, respectively.

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Determination of the Galactic Rotation Parameters from Cepheid Radial Velocities and their Variation with the Distance Scale.

The Astronomical Journal ◽

10.1086/109450 ◽

1964 ◽

Vol 69 ◽

pp. 544 ◽

Cited By ~ 1

Author(s):

W. E., III Howard ◽

J. G. Kirk

Keyword(s):

Radial Velocities ◽

Distance Scale ◽

Galactic Rotation ◽

Rotation Parameters

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Atmospheric limitations of the accuracy of determination of earth rotation parameters

Measurement Techniques ◽

10.1007/bf00864086 ◽

1986 ◽

Vol 29 (4) ◽

pp. 282-284

Author(s):

L. S. Yunoshev

Keyword(s):

Earth Rotation ◽

Earth Rotation Parameters ◽

Rotation Parameters

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Milky Way Rotation Models from Neutral Hydrogen and Molecular Clouds: Galactic Constants, Common Details and Differences

International Astronomical Union Colloquium ◽

10.1017/s0252921100055378 ◽

2000 ◽

Vol 174 ◽

pp. 403-407

Author(s):

Igor’ I. Nikiforov

Keyword(s):

Milky Way ◽

Galactic Center ◽

Kinematic Model ◽

Neutral Hydrogen ◽

Galactic Rotation ◽

Kinematic Data ◽

Galactic Rotation Curve ◽

The Common ◽

Center Distance

Kinematic data from neutral hydrogen observations provide information to solve the interdependent problems of the determination of the main Galactic constants (the Solar-Galactic center distance R0, the Oort constant A and others) and the Galactic rotation curve (Nikiforov & Petrovskaya 1994, hereafter NP94, and references therein). However, in the standard method for finding R0 by comparing the rotations of HI clouds and some other objects (typically HII regions/CO clouds), the kinematic model, constructed typically solely from HI data, is considered to be the same for both galactic subsystems (e.g. Merrifield 1992). In practice a discrepancy between their rotation curves can produce strongly erroneous results (Merrifield 1992, NP94). Establishing the common rotation law from HI plus HII/CO data in NP94 is only a part of attacking the problem.

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Galactic rotation parameters from data on open star clusters

Astronomy Letters ◽

10.1134/s1063773707110023 ◽

2007 ◽

Vol 33 (11) ◽

pp. 720-728 ◽

Cited By ~ 16

Author(s):

V. V. Bobylev ◽

A. T. Bajkova ◽

S. V. Lebedeva

Keyword(s):

Star Clusters ◽

Galactic Rotation ◽

Open Star Clusters ◽

Open Star ◽

Rotation Parameters

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Determination of the C/M5+ Ratio in the Galactic Disk

International Astronomical Union Colloquium ◽

10.1017/s025292110002203x ◽

1995 ◽

Vol 148 ◽

pp. 276-279

Author(s):

Francisco J. Fuenmayor

Keyword(s):

Near Infrared ◽

Galactic Center ◽

Galactic Disk ◽

Mean Value ◽

Galactocentric Distance ◽

The Galaxy ◽

Metal Abundance ◽

Objective Prism ◽

M Stars

AbstractA determination of the C/M5+ ratio, as a function of the galactocentric distance, in the galactic disk is presented. These results are based upon previous determinations of the space density for cool carbon stars and for late giant M stars in the Milky Way. Most of these results were obtained from objective-prism surveys in the near infrared using mainly Schmidt-type telescopes. The ratio C/M5+ appears to increase from 0.05 to 0.25 in the galactic disk, from the galactic center outwards. A mean value of 0.15 of this ratio for the Galaxy is suggested. Correlations between the C/M5+ ratio and currently known metal abundance gradients in the galactic disk are discussed.

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