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.

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 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 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 Galactocentric distance of the Sun derived from kinematic data

2012 ◽  
Vol 8 (S289) ◽  
pp. 444-447 ◽  
Author(s):  
Zi Zhu ◽  
Ming Shen
Keyword(s):  
Galactic Center ◽  
Galactic Disk ◽  
Kinematic Model ◽  
Open Clusters ◽  
Galactocentric Distance ◽  
Kinematic Data ◽  
Classical Cepheids ◽  
Circular Rotation ◽  
Radial Velocity Data

AbstractBased on radial velocity data and Hipparcos proper motions, we present a new determination of the Galactocentric distance based on a purely kinematic model. We have selected three subgroups of Galactic thin-disk components (O–B5 stars, classical Cepheids and Galactic open clusters) to trace the local structure and kinematics of the Galactic disk. Adopting the approximation of axisymmetric circular rotation, we have derived the Sun's distance to the Galactic Center, R0 = 8.25 ± 0.79 kpc based on O–B5 stars, R0 = 7.98 ± 0.79 kpc based on Galactic Cepheids and R0 = 8.03 ± 0.70 kpc using open clusters, all of which are in excellent agreement with the current-best estimate of the Galactocentric distance.

scholarly journals The Milky Way thin disk structure as revealed by stars and young open clusters

2013 ◽  
Vol 9 (S298) ◽  
pp. 7-16 ◽  
Author(s):  
Giovanni Carraro
Keyword(s):  
Milky Way ◽  
Spiral Structure ◽  
Galactic Center ◽  
Galactic Disk ◽  
Chemical Properties ◽  
Thin Disk ◽  
Open Clusters ◽  
Disk Structure ◽  
The Status ◽  
The Impact

AbstractIn this contribution I shall focus on the structure of the Galactic thin disk. The evolution of the thin disk and its chemical properties have been discussed in detail by T. Bensby's contribution in conjunction with the properties of the Galactic thick disk, and by L.Olivia in conjunction with the properties of the Galactic bulge. I will review and discuss the status of our understanding of three major topics, which have been the subject of intense research nowadays, after long years of silence: (1) the spiral structure of the Milky Way, (2) the size of the Galactic disk, and (3) the nature of the Local arm (Orion spur), where the Sun is immersed. The provisional conclusions of this discussion are that: (1) we still have quite a poor knowledge of the Milky Way spiral structure, and the main disagreements among various tracers are still to be settled; (2) the Galactic disk does clearly not have an obvious luminous cut-off at about 14 kpc from the Galactic center, and next generation Galactic models need to be updated in this respect, and (3) the Local arm is most probably an inter-arm structure, similar to what we see in several external spirals, like M 74. Finally, the impact of Gaia and LAMOST in this field will be briefly discussed as well.

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

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.

scholarly journals An Overview of the Globular Cluster System of the Galaxy

1988 ◽  
Vol 126 ◽  
pp. 37-48
Author(s):  
Robert Zinn
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
Cluster System ◽  
Open Clusters ◽  
The Galaxy ◽  
Globular Cluster System ◽  
Harlow Shapley

Harlow Shapley (1918) used the positions of globular clusters in space to determine the dimensions of our Galaxy. His conclusion that the Sun does not lie near the center of the Galaxy is widely recognized as one of the most important astronomical discoveries of this century. Nearly as important, but much less publicized, was his realization that, unlike stars, open clusters, HII regions and planetary nebulae, globular clusters are not concentrated near the plane of the Milky Way. His data showed that the globular clusters are distributed over very large distances from the galactic plane and the galactic center. Ever since this discovery that the Galaxy has a vast halo containing globular clusters, it has been clear that these clusters are key objects for probing the evolution of the Galaxy. Later work, which showed that globular clusters are very old and, on average, very metal poor, underscored their importance. In the spirit of this research, which started with Shapley's, this review discusses the characteristics of the globular cluster system that have the most bearing on the evolution of the Galaxy.

scholarly journals Probing the structure of the Galactic disk through open clusters

2009 ◽  
Vol 5 (S266) ◽  
pp. 482-482
Author(s):  
Xiaoying Pang ◽  
Chenggang Shu
Keyword(s):  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Age Distribution ◽  
Outer Part ◽  
Simulation Models ◽  
Open Clusters ◽  
Galactocentric Distance ◽  
Distance Measurements ◽  
The Galaxy

AbstractThe WEBDA database of open clusters (hereafter OCs) in the Galaxy contains 970 OCs, of which 911 have age determinations, 920 have distance measurements, and 911 have color-excess data. Base on the statistical analysis of global properties of open clusters, we investigate disk properties such as the height above the Galactic plane. We find that old open clusters (age ≥ 1 Gyr) are preferentially located far from the Galactic plane with 〈|z|〉~394.5 pc. They lie in the outer part of the Galactic disk. The young open clusters are distributed in the Galactic plane almost symmetrically with respect to the Sun, with a scale height perpendicular to the Galactic plane of 50.5 pc. The age distribution of open clusters can be fit approximately with a two-component exponential decay function: one component has an age scale factor of 225.2 Myr, and the other consists of longer-lived clusters with an age scale of 1.8 Gyr, which are smaller than those derived by Janes & Phelps (1994) of 200 Myr and 4 Gyr for the young and old OCs, respectively. As a consequence of completeness effects, the observed radial distribution of OCs with respect to Galactocentric distance does not follow the expected exponential profile. Instead, it falls off both for regions external to the solar circle and more sharply towards the Galactic Center, which is probably due to giant molecular cloud disruption in the center. We simulate the effects of completeness, assuming that the observed distribution of the number of OCs with a given number of stars above the background is representative of the intrinsic distribution of OCs throughout the Galaxy. Two simulation models are considered, in which the intrinsic number of the observable stars are distributed (i) assuming the actual positions of the OCs in the sample, and (ii) random selection of OC positions. As a result, we derive completeness-corrected radial distributions which agree with an exponential disk throughout the observed Galactocentric distance in the range of 5–15 kpc, with scale lengths in the range of 1.6–2.8 kpc.

scholarly journals Population and Evolution of Pulsating A-F Stars

1995 ◽  
Vol 164 ◽  
pp. 364-364
Author(s):  
Jiang Shiyang ◽  
Liu Yanying
Keyword(s):  
White Dwarfs ◽  
Main Sequence ◽  
Rotation Velocity ◽  
Light Variation ◽  
Galactic Rotation ◽  
Strongly Correlated ◽  
The Galaxy ◽  
The Mean ◽  
F Stars ◽  
Rotation Constant

Pulsating A-F variables include all the stellar types listed in teh Table, as well as the pulsating white dwarfs. Stars near the zero-age-main-sequence have faster rotation velocity, which slows as expected with age (Villata 1992) and a smaller amplitude of light variation, so we suggest that rotation velocity be considered in Population classifications. Also, in the Galaxy, the galactic rotation constant A is related to stellar age T by: A(kms−1kpc−1) = (−2.4±0.8)T(109yr) + (32±2) (Kharchenko 1992). The linear rotation velocity is also a function of the Z coordinate of the object inside the Galaxy: the mean Z-gradient is −10kms−1kpc−1 (Malakhova & Petrovskaya, 1992). Thus the population is strongly correlated with the rotation velocity and the evolutionary age.

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