The circular velocity at the sun

1979 ◽  
Vol 84 ◽  
pp. 225-230
Author(s):  
G. R. Knapp
Keyword(s):  
Globular Clusters ◽  
Galactic Center ◽  
Solar Rotation ◽  
Center Of Mass ◽  
Rotation Velocity ◽  
Current Evidence ◽  
Galactic Rotation ◽  
The Sun ◽  
Galactocentric Distance ◽  
Rr Lyrae

The galactic rotation velocity at the Sun, , can be derived several ways, none of them direct and unambiguous - (1) the solar velocity can be found relative to the halo population (the RR Lyrae stars, globular clusters etc.), but may contain an unknown contribution from possible systematic rotation of the halo system (2) the product Ro ω(Ro) = Ro (A-B) can be calculated but is uncertain because of large uncertainties in each of these three quantities (3) the motion of the Sun with respect to the center of the Local Group can be found but includes the motion of the galactic center of mass and (4) the velocity-longitude dependence of the outer HI boundary can be examined to deduce the most likely value of . The incorporation of new data into analyses using methods (1) and (3) gives essentially the same answers as older studies. Examination of the accumulated current evidence suggests that the best values for the solar rotation velocity and the galactocentric distance Ro are 220 km s−1 and 8.5 kpc respectively.

scholarly journals Structure and kinematics of the Milky Way spirals traced by open clusters

2007 ◽  
Vol 3 (S248) ◽  
pp. 462-465
Author(s):  
Z. Zhu
Keyword(s):  
Milky Way ◽  
Galactic Center ◽  
Rotation Velocity ◽  
Open Clusters ◽  
Galactic Rotation ◽  
The Sun ◽  
Galactocentric Distance ◽  
Disk Structure ◽  
Circular Rotation ◽  
The Mean

AbstractSelecting 301 open clusters with complete spatial velocity measurements and ages, we are able to estimate the disk structure and kinematics of the Milky Way. Our analysis incorporates the disk scale height, the circular velocity of the Galactic rotation, the Galactocentric distance of the Sun and the ellipticity of the weak elliptical potential of the disk. We have derived the distance of the Sun to the Galactic center R0=8.03±0.70 kpc, that is in excellent agreement with the literature. From kinematic analysis, we found an age-dependent rotation of the Milky Way. The mean rotation velocity of the Milky Way is obtained as 235±10 km s−1. Using a dynamic model for an assumed elliptical disk, a clear weak elliptical potential of the disk with ellipticity of ε(R0) = 0.060±0.012 is detected, the Sun is found to be near the minor axis with a displacement of 30°±3°. The motion of clusters is suggested to be on elliptical orbits other than the circular rotation.

scholarly journals Measurements of annual parallaxes and proper motions of the red supergiant S Per

2007 ◽  
Vol 3 (S242) ◽  
pp. 378-380 ◽  
Author(s):  
Yoshiharu Asaki ◽  
Shuji Deguchi ◽  
Hirishi Imai ◽  
Kazuya Hachisuka ◽  
Makoto Miyoshi ◽  
...  
Keyword(s):  
Water Vapor ◽  
Proper Motion ◽  
Galactic Center ◽  
Rotation Velocity ◽  
Galactic Rotation ◽  
The Sun ◽  
Proper Motions ◽  
Right Ascension

AbstractVLBI phase-referencing monitoring of water vapor masers around the red supergiant, S Per, was conducted over four years. We successfully obtained proper motions and an annual parallax of the masers and determined the distance to S Per of 2.51±0.09 kpc. The proper motion of the star itself was inferred from the maser proper motions, and it was −0.38 and −1.54 mas/yr for right ascension and declination, respectively. Assuming the distance from the sun to the Galactic center, R0, of 8.5 kpc and the rotation velocity around the sun, Θ0, of 220 km/s, the Galactic rotation velocity around S Per is 200 km/s.

scholarly journals Proper-Motion Based Kinematics Study of Galactic RR Lyraes

2015 ◽  
Vol 11 (S317) ◽  
pp. 290-291
Author(s):  
Andrei K. Dambis ◽  
Leonid N. Berdnikov ◽  
Alexei S. Rastorguev ◽  
Marina V. Zabolotskikh
Keyword(s):  
Radial Velocity ◽  
Proper Motion ◽  
Velocity Dispersion ◽  
Galactic Center ◽  
The Sun ◽  
Proper Motions ◽  
Galactocentric Distance ◽  
Rr Lyrae

AbstractWe use the UCAC4 and SDSS proper motions of about 7500 RR Lyrae type variables located within ~10 kpc from the Sun to study the dependence of their velocity ellipsoid on Galactocentric distance in the RG = 3–17 kpc interval. The radial velocity dispersion, σVR, decreases from ~190 km/s at RG = 3.5–5.5 kpc down to ~100 km/s at RG = 13–15 kpc, and the σVT/σVR ratio remains virtually constant (σVT/σVR ~0.54–0.64) in the Galactocentric distance interval from RG = 4.5 kpc to RG = 10.5 kpc increasing to ~0.9 both toward the Galactic center and beyond RG = 11 kpc.

scholarly journals Astrometry of Galactic Star-Forming Regions ON1 and ON2N with VERA

2012 ◽  
Vol 8 (S287) ◽  
pp. 391-395 ◽  
Author(s):  
Takumi Nagayama ◽  
Keyword(s):  
Three Dimensional ◽  
Rotation Velocity ◽  
Galactic Rotation ◽  
The Sun ◽  
Angular Rotation ◽  
Star Forming ◽  
Star Forming Regions ◽  
Circular Rotation

AbstractWe conducted the astrometry of H2O masers in the Galactic star-forming regions ON1 and ON2N with the VLBI Exploration of Radio Astrometry (VERA). The measured distances to ON1 and ON2N are 2.47±0.11 kpc and 3.83±0.13 kpc, respectively. In the case that ON1 and ON2N are on a perfect circular rotation, we estimate the angular rotation velocity of the Galactic rotation at the Sun (the ratio of the Galactic constants) to be 28 ± 2 km s−1 kpc−1 using the measured distances and three-dimensional velocity components of ON1 and ON2N. This value is larger than the IAU recommended value of 25.9 km s−1 kpc−1, but consistent with other results recently obtained with the VLBI technique.

scholarly journals A New Value for the Rotation Speed of the Spiral Structure

1977 ◽  
Vol 45 ◽  
pp. 293-296 ◽  
Author(s):  
J. Palouš
Keyword(s):  
Surface Density ◽  
Galactic Center ◽  
Local Density ◽  
Outer Part ◽  
Density Variation ◽  
The Sun ◽  
Basic Model ◽  
Rr Lyrae ◽  
The Galaxy ◽  
Nearby Stars

The basic model of our Galaxy, like the Schmidt (1965) model, obeys the density law ρ(R) for the Galaxy based on divers evidence, less or better known from observation. The interpretation of the interstellar hydrogen radio profiles yields the rotation curve and the run of the force component in the radial direction. The Oort constants A, B known from radial velocities and proper motions of nearby stars, the distance from the Sun to the galactic center Roestablished from the distances of RR Lyrae stars, the local density and density gradients in the vicinity of the Sun, known from the star counts, are involved in this basic model of the Galaxy. The r.m.s. velocity component in the z direction yields the approximate mass distribution in this direction. The model surface density is computed by integrating the density along the z direction in the model. The local surface density in the Schmidt model is 114 solar masses per pc2; it depends rather strongly on the assumed density variation in the outer part of the Galaxy.

The Rotation Curve from A-F Supergiants

1996 ◽  
Vol 169 ◽  
pp. 703-706
Author(s):  
D. M. Peterson ◽  
D. Slowik
Keyword(s):  
Total Mass ◽  
Rotation Curve ◽  
Galactic Center ◽  
Galactic Rotation ◽  
The Sun ◽  
Critical Information ◽  
New Class ◽  
The Galaxy ◽  
Local Distance

The Galactic rotation law provides critical information for estimating the distribution of mass in the Galaxy, for tying the distance of the Sun from the Galactic center to local distance scales, and, if determined over large enough distances, for estimating the total mass of the system and the amount of nonluminous matter present. Interior to the Sun velocities are well defined by observations of the ISM, particularly HI. These techniques are not available for points exterior to the Sun and we must rely on observations of velocities of objects whose distances can be estimated. Notable among these are the Cepheids (Pont et al 1994) and the combination of CO velocities and OB cluster distances (Brand & Blitz 1993) where the two are found to coexist. Adding a new class of objects, particularly bright, relatively common objects to this effort is of importance.

scholarly journals Stellar parameters in the bulge cluster NGC 6553

1997 ◽  
Vol 189 ◽  
pp. 203-206 ◽  
Author(s):  
B. Barbuy ◽  
S. Ortolani ◽  
E. Bica ◽  
A. Renzini ◽  
M.D. Guarnieri
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Spectroscopic Analysis ◽  
Galactic Center ◽  
Stellar Populations ◽  
The Sun ◽  
Galactic Bulge ◽  
Complete Understanding ◽  
Luminosity Functions ◽  
Bulge Formation

Globular clusters in the Galactic bulge form a flattened system, extending from the Galactic center to about 4.5 kpc from the Sun (Barbuy et al. 1997). A study of abundance ratios in these clusters is very important for a more complete understanding of the bulge formation. In this work we present a spectroscopic analysis of individual stars in NGC 6553. This cluster is a key one because it is located at d⊙ ≍ 5.1 kpc, therefore relatively close to us, and at the same time it is representative of the Galactic bulge stellar population: (a) Ortolani et al. (1995) showed that NGC 6553 and NGC 6528 show very similar Colour-Magnitude Diagrams (CMDs), and NGC 6528 is located at d⊙ ≍ 7.83 kpc, very close to the Galactic center; (b) the stellar populations of the Baade Window is also very similar to that of NGC 6553 and NGC 6528 as Ortolani et al. (1995) have shown by comparing their luminosity functions.

10.3. Progress toward a trigonometric parallax of Sgr A∗

1998 ◽  
Vol 184 ◽  
pp. 435-436
Author(s):  
M. J. Reid ◽  
A. C. S. Readhead ◽  
R. Vermeulen ◽  
R. Treuhaft
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Galactic Center ◽  
The Sun ◽  
Secular Motion ◽  
Extragalactic Source ◽  
Trigonometric Parallax ◽  
Sgr A ◽  
Harlow Shapley ◽  
Astronomy And Astrophysics

In 1918, Harlow Shapley first noted that globular clusters were concentrated toward the constellation of Sagittarius, and hence the Sun was not near the center of the Milky Way. Since that time astronomers have expended considerable effort to determine the distance to the center of the Milky Way, because any change in the value of this distance, R0, has a widespread impact on astronomy and astrophysics. Beginning in 1991, we have conducted observations with the VLBA designed to make possible a program to measure the distance to the Galactic Center via a trigonometric parallax. This could be accomplished with the VLBA using Sgr A∗ as a phase reference for one or more (weaker) compact extragalactic sources. A time series of measurements of the position of Sgr A∗ relative to an extragalactic source should show the effects of the annual ≈ ±0.12 mas signature of the Earth's orbit around the Sun (trigonometric parallax), as well as the ≈ 6 mas yr−1 secular motion caused by the Sun's orbit around the Galactic Center.

Modelling the Milky Way with Gaia-TGAS

2017 ◽  
Vol 12 (S330) ◽  
pp. 222-224
Author(s):  
Jason A. S. Hunt
Keyword(s):  
Angular Momentum ◽  
Milky Way ◽  
Solar Rotation ◽  
Rotation Velocity ◽  
Solar Neighbourhood ◽  
Galactic Centre ◽  
Galactic Rotation ◽  
Perseus Arm

AbstractI summarize two recent projects involving the Gaia-TGAS data. Firstly, I discuss a detection of a lack of disc stars in the Solar neighbourhood with velocities close to zero angular momentum. We use predictions of this effect to make a measurement of the Solar rotation velocity around the Galactic centre, and also of R0. Secondly, I discuss a detection of a group of stars with systematically high Galactic rotation velocity. We propose that it may be caused by the Perseus arm and compare the data with simulations.

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