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

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.

scholarly journals The Galactic Rotation Curve to R = 18 Kpc

1980 ◽  
Vol 87 ◽  
pp. 213-220 ◽  
Author(s):  
Leo Blitz ◽  
Michel Fich ◽  
Antony A. Stark
Keyword(s):  
Rotation Curve ◽  
Hii Regions ◽  
Molecular Gas ◽  
Galactic Rotation ◽  
Galactocentric Distance ◽  
The Past ◽  
The Galaxy ◽  
Galactic Rotation Curve ◽  
Sizable Number

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.

scholarly journals Determination of the Solar Galactocentric Distance from the Kinematics of Masers

2015 ◽  
Vol 24 (1) ◽  
Author(s):  
A. T. Bajkova ◽  
V. V. Bobylev
Keyword(s):  
Galactic Rotation ◽  
Galactocentric Distance ◽  
Solar Galactocentric Distance

AbstractWe determine the parameters of Galactic rotation and the solar galactocentric distance

scholarly journals OH/IR Stars Near the Galactic Centre

1983 ◽  
Vol 103 ◽  
pp. 542-543
Author(s):  
H.J. Habing ◽  
F.M. Olnon ◽  
A. Winnberg ◽  
H.E. Matthews ◽  
B. Baud
Keyword(s):  
Spatial Distribution ◽  
High Velocity ◽  
Surface Brightness ◽  
Velocity Dispersion ◽  
Galactic Centre ◽  
Galactic Rotation ◽  
Red Giants ◽  
Large Array ◽  
Very Large Array ◽  
Ir Stars

We have detected 34 OH/IR stars within 1 degree of the galactic centre by their OH emission line at 1612 MHz (18 cm) using the Effelsberg 100 m telescope and the Very Large Array. The spatial distribution and the distribution of the radial velocities show that practically all stars are within 150 pc from the Galactic centre, and that the number of foreground objects is very small. The projected distribution of the stars is similar to that of the surface brightness at 2.4 μm. Since the 2.4 μm radiation is supposed to be due to red giants, the OH/IR stars are probably members of the same population. The stars have considerable random velocities (velocity dispersion in one coordinate of 150 ± 50 km s−1), but show general Galactic rotation. The high velocity dispersion is remarkable for objects of this population.

scholarly journals Kinematics and multiband period–luminosity–metallicity relation of RR Lyrae stars via statistical parallax

2021 ◽  
Vol 502 (3) ◽  
pp. 4074-4092
Author(s):  
T D Muhie ◽  
A K Dambis ◽  
L N Berdnikov ◽  
A Y Kniazev ◽  
E K Grebel
Keyword(s):  
Large Magellanic Cloud ◽  
Galactic Centre ◽  
Galactic Rotation ◽  
Distance Modulus ◽  
Wide Field ◽  
Motion Data ◽  
V Band ◽  
Rr Lyrae ◽  
Photometric Observations ◽  
Zero Points

ABSTRACT This paper presents results from photometric and statistical-parallax analysis of a sample of 850 field RR Lyrae (RRL) variables. The photometric and spectroscopic data for our sample of RRLs are obtained from (1) our new spectroscopic observations (for 448 RRLs) carried out with the Southern African Large Telescope; (2) our photometric observations using the 1.0-m telescope of the South African Astronomical Observatory, and (3) literature. These are combined with accurate proper motion data from the second data release of the Gaia mission (DR2). This study primarily determines the velocity distribution of solar neighbourhood RRLs, and it also calibrates the zero-points of the RRLs’ visual V-band luminosity–metallicity (LZ or MV–[Fe/H]) relation and their period–luminosity–metallicity (PLZ) relations in the Wide-field Infrared Survey ExplorerW1 and Two-Micron All-Sky Survey Ks bands. We find the bulk velocity of the halo RRLs relative to the Sun to be (U0, V0, W0)Halo =(− 16 ± 7, −219 ± 7, −6 ± 5) km s−1 in the direction of Galactic centre, Galactic rotation, and North Galactic pole, respectively, with velocity-dispersion ellipsoids (σVR, σVϕ, σVθ)Halo = (153 ± 7, 106 ± 4, 101 ± 4) km s−1. The corresponding parameters for the disc component are found to be (U0, V0, W0)Disc = (− 19 ± 5, −46 ± 5, −14 ± 3) km s−1 and (σVR, σVϕ, σVθ)Disc =(49 ± 4, 38 ± 4, 25 ± 3) km s−1. The calibrated PLZ in W1-, Ks-, and V-band LZ relations are $\langle \, M_{W1}\rangle =$  $-0.824+0.124[\mathrm{ Fe/H}]-2.381\log \, P_F$, 〈MKs〉 = $-0.804+0.101[\mathrm{ Fe/H}]-2.33\log \, P_F$, and $\langle \, M_V\rangle =1.041+0.232[\mathrm{ Fe/H}]$, respectively. The calibrated PLZ and LZ relations are used to estimate the Galactic Centre distance and the distance modulus of the Large Magellanic Cloud (LMC), which are found to be 7.99 ± 0.49 kpc and 18.46 ± 0.09  mag, respectively. All our results are in excellent agreement with available literature based on statistical-parallax analysis, but are considerably more accurate and precise. Moreover, the zero-points of our calibrated PLZ and LZ relations are quite consistent with current results found by other techniques and yield an LMC distance modulus that is within 0.04 mag of the current most precise estimate.

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 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 Galactic mass and anisotropy profile with halo K-giant and blue horizontal branch stars from LAMOST/SDSS and Gaia

2019 ◽  
Vol 14 (S353) ◽  
pp. 91-95
Author(s):  
Sarah A. Bird ◽  
Xiang-Xiang Xue ◽  
Chao Liu ◽  
Juntai Shen ◽  
Chris Flynn ◽  
...  
Keyword(s):  
Velocity Dispersion ◽  
Galactic Halo ◽  
Anisotropy Parameter ◽  
Horizontal Branch ◽  
Stellar Kinematics ◽  
Horizontal Branch Stars ◽  
Wide Range ◽  
Stellar Halo ◽  
Mass Profile

AbstractA major uncertainty in the determination of the mass profile of the Milky Way using stellar kinematics in the halo is the poorly determined anisotropy parameter, , where σr is the Galactocentric radial velocity dispersion, and σθ and σφ are the tangential components of the velocity dispersion. We have used a sample of over 24,000 Galactic halo K giant and blue horizontal branch stars from the LAMOST stellar spectroscopic survey and SDSS/SEGUE, combined with proper motions from Gaia Data Release 2, to measure β(rgc) over a wide range of Galactocentric distances rgc from 5 to 80 kpc. Kinematic substructures have been carefully removed to reveal the underlying diffuse stellar halo prior to measuring β. We find that orbits are generally radial (β > 0) and β is constant out to distances of about 40 kpc, with a dependence on metallicity of the stars, such that β declines with lower metallicity. Similar behavior is seen in both the K giant and BHB samples.

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 Galaxy properties as revealed by MaNGA – III. Kinematic profiles and stellar population gradients in S0s

2020 ◽  
Vol 495 (3) ◽  
pp. 2894-2908 ◽  
Author(s):  
H Domínguez Sánchez ◽  
M Bernardi ◽  
F Nikakhtar ◽  
B Margalef-Bentabol ◽  
R K Sheth
Keyword(s):  
Stellar Population ◽  
Velocity Dispersion ◽  
Signal To Noise Ratio ◽  
Elliptical Galaxies ◽  
Element Abundance ◽  
High Signal ◽  
Galactocentric Distance ◽  
Massive Galaxies ◽  
Nearby Galaxies ◽  
Mass Functions

ABSTRACT This is the third paper of a series where we study the stellar population gradients (SP; ages, metallicities, α-element abundance ratios, and stellar initial mass functions) of early-type galaxies (ETGs) at $z$ ≤ 0.08 from the Mapping Nearby Galaxies at APO Data Release 15 (MaNGA-DR15) survey. In this work, we focus on the S0 population and quantify how the SP varies across the population as well as with galactocentric distance. We do this by measuring Lick indices and comparing them to SP synthesis models. This requires spectra with high signal-to-noise ratio which we achieve by stacking in bins of luminosity (Lr) and central velocity dispersion (σ0). We find that: (1) there is a bimodality in the S0 population: S0s more massive than $3\times 10^{10}\, \mathrm{M}_\odot$ show stronger velocity dispersion and age gradients (age and σr decrease outwards) but little or no metallicity gradient, while the less massive ones present relatively flat age and velocity dispersion profiles, but a significant metallicity gradient (i.e. [M/H] decreases outwards). Above $2\times 10^{11}\, \mathrm{M}_\odot$, the number of S0s drops sharply. These two mass scales are also where global scaling relations of ETGs change slope. (2) S0s have steeper velocity dispersion profiles than fast-rotating elliptical galaxies (E-FRs) of the same luminosity and velocity dispersion. The kinematic profiles and SP gradients of E-FRs are both more similar to those of slow-rotating ellipticals (E-SRs) than to S0s, suggesting that E-FRs are not simply S0s viewed face-on. (3) At fixed σ0, more luminous S0s and E-FRs are younger, more metal rich and less α-enhanced. Evidently for these galaxies, the usual statement that ‘massive galaxies are older’ is not true if σ0 is held fixed.

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