Determination of the Solar Galactocentric Distance from the Kinematics of 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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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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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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The Galactic distribution of Wolf-Rayet stars: an optical and infrared approach

Symposium - International Astronomical Union ◽

10.1017/s007418090021262x ◽

2003 ◽

Vol 212 ◽

pp. 441-450 ◽

Cited By ~ 5

Author(s):

Karel A. van der Hucht

Keyword(s):

Surface Density ◽

Local Group ◽

Galactic Center ◽

Solar Neighborhood ◽

Galactocentric Distance ◽

Preliminary Results ◽

Number Ratio ◽

Photometric Distance ◽

Galactic Distribution

The recent VIIth Catalogue of Galactic Wolf-Rayet Stars (van der Hucht 2001), lists 227 Population I WR stars, comprising 127 WN, 87 WC, 10 WN/WC and 3 WO stars. Additional discoveries since then bring the census to ≳ 253 WR stars, including ≳ 27 WNL and 13 WCL stars within 50 pc of the Galactic Center. A re-determination of the optical photometric distances and the galactic distribution of WR stars shows in the solar neighbourhood (d < 3 kpc) a projected surface density of 2.7 WR stars per kpc2, a NWC/NWN number ratio of 1.3, and a WR binary frequency of 40%. Compared with other Local Group galaxies, the NWC/NWN number ratio in the solar neighborhood is a factor ~2 above the observed metallicity-dependent trend. This could imply that some 30 galactic WN stars in the d < 3 kpc volume are still hiding. Preliminary results of infrared photometric distance determinations are shown. The galactocentric distance (RWR) distribution per subtype shows RWN and RWC decreasing with later WN and WC subtypes. The observed trend is more indicative of WNE → WCE and WNL → WCL subtype evolution than of WNL → WNE and WCL → WCE subtype evolution.

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The transition between the thick and thin Galactic disks

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308019807 ◽

2007 ◽

Vol 3 (S248) ◽

pp. 458-461

Author(s):

M. Haywood

Keyword(s):

Stellar Populations ◽

Thin Disk ◽

Solar Neighbourhood ◽

Galactic Disks ◽

Local Data ◽

Galactocentric Distance ◽

The Status ◽

Solar Galactocentric Distance ◽

Thick Disks ◽

Thin Disks

AbstractWe study the transition between the thick and thick disks using solar neighbourhood data, focusing in particular on the status of local metal-poor thin disk stars ([Fe/H]<−0.3 dex, [α/Fe]<0.1 dex). The orbital properties of these stars, which are responsible for the hiatus in metallicity between the two disks, suggest that they most likely originate from the outer Galactic thin disk. It implies that the transition between the two stellar populations at a solar galactocentric distance must have occurred at a metallicity of about −0.3 dex. Transition stars at this metallicity are in fact present in local samples and fill the gap in α-element between the thick and thin disks. These results imply that, at least from the local data, there is a clear evolutionary link between the thick and thin disks.

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Using the environment to understand supernova properties

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313009770 ◽

2013 ◽

Vol 9 (S296) ◽

pp. 350-351

Author(s):

Lluís Galbany ◽

Vallery Stanishev ◽

Ana Mourão

Keyword(s):

Direct Determination ◽

Environmental Parameters ◽

Host Galaxy ◽

Host Galaxies ◽

Galactocentric Distance ◽

Elemental Abundances ◽

Integral Field Spectroscopy ◽

Significant Difference ◽

Integral Field

AbstractWe present three studies that use supernova (SN) environments within host galaxies (HGs) to constrain SNe properties. These studies are ordered from an indirect approximation to a direct determination of the environmental parameters of the SN. We find correlations between the galactocentric distance and several parameters measured from both the SN light-curve (LC) and the host galaxy spectroscopy. We are able to recover and strength previous results pointing to a sequence on the progenitor mass of different SN types. We also confirm no significant difference in the elemental abundances of the environment where different SN types exploded, measured with a more powerful technique such as Integral Field Spectroscopy (IFS).

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The circular velocity at the sun

Symposium - International Astronomical Union ◽

10.1017/s0074180900014510 ◽

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.

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