Galactic Rotation Velocity Research Articles

Modelling the Milky Way with Gaia-TGAS

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.

Calculating the MOND constant and addressing flat galactic orbital star rotation velocity curves

<p class="abstract"><span lang="EN-US">A particle based explanation for the MOND constant, a<sub>o</sub>, is proposed. For stars orbiting in the outer region of galaxies Newton’s inverse square law fails at the same classical angular acceleration v<sup>2</sup>/R, (= a<sub>o</sub>), regardless of the mass of the galaxy or star, the star orbital velocity v, or the orbit radius R. Gravitational orbital dynamics, where orbital matter propagates un-accelerated in curved space-time as described by General Relativity, applies equally to systems of vastly different masses, i.e. at cosmological and elementary particle scales, with gravity simply an observer domain manifestation of the force localizing electromagnetic energy to form particles. Comparison of astronomical data and particle concepts, with scale adjustments, enables an expression for a<sub>o</sub> to be derived and a numerical value obtained within the uncertainty bounds of empirical data. Newton’s law fails and stellar orbital velocities become independent of the orbit radius at the same gravitational field strength as at the proton radius. A quantum loop based cause of orbital velocity curve flattening is proposed.</span></p>

TRIGONOMETRIC DISTANCE AND PROPER MOTION OF IRAS 20056+3350: A MASSIVE STAR FORMING REGION ON THE SOLAR CIRCLE

We report our measurement of the trigonometric distance and proper motion of IRAS 20056+3350, obtained from the annual parallax of H2O masers. Our distance of D = 4.69 +0.65 −0.51 kpc, which is 2.8 times larger than the near kinematic distance adopted in the literature, places IRAS 20056+3350 at the leading tip of the Local arm and proximal to the Solar circle. Using our distance we re-evaluate past observations to reveal IRAS 20056+3350 as a site of massive star formation at a young stage of evolution. This result is consistent with the spectral energy distribution of the source evaluated with published photometric data from UKIDSS, WISE, AKARI, IRAS and sub-millimetre continuum. Both analytical approaches reveal the luminosity of the region to be 2.4×10 4 L⊙, and suggest that IRAS 20056+3350 is forming an embedded star of ≥16M⊙. We estimated the proper motion of IRAS 20056+3350 to be (µ�cos�, µ�) = (−2.62±0.33, −5.65±0.52) mas yr −1 from the group motion of H2O masers, and use our results to estimate the angular velocity of Galactic rotation at the Galactocentric distance of the Sun, 0 = 29.75±2.29 km s −1 kpc −1 ,

Determination of the galactic rotation curve from OB stars

We consider three samples of O- and B-type stars from the solar neighborhood 0.6--4 kpc for which we have taken the distances, line-of-sight velocities, and proper motions from published sources. The first sample contains 120 massive spectroscopic binaries. O stars with spectroscopic distances from Patriarchi et al. constitute the second sample. The third sample consists of 168 OB3 stars whose distances have been determined from interstellar calcium lines. The angular velocity of Galactic rotation at the solar distance $\Omega_0,$ its two derivatives $\Omega'_0$ and $\Omega"_0,$ and the peculiar velocity components of the Sun $(U,V,W)_\odot$ are shown to be well determined from all three samples of stars. They are determined with the smallest errors from the sample of spectroscopic binary stars and the sample of stars with the calcium distance scale. The fine structure of the velocity field associated with the influence of the Galactic spiral density wave clearly manifests itself in the radial velocities of spectroscopic binary stars and in the sample of stars with the calcium distance scale.

The Araucaria Project: accurate stellar parameters and distance to evolved eclipsing binary ASAS J180057-2333.8 in Sagittarius Arm

We have analyzed the double-lined eclipsing binary system ASAS J180057-2333.8 from the All Sky Automated Survey (ASAS) catalogue . We measure absolute physical and orbital parameters for this system based on archival $V$-band and $I$-band ASAS photometry, as well as on high-resolution spectroscopic data obtained with ESO 3.6m/HARPS and CORALIE spectrographs. The physical and orbital parameters of the system were derived with an accuracy of about 0.5 - 3%. The system is a very rare configuration of two bright well-detached giants of spectral types K1 and K4 and luminosity class II. The radii of the stars are $R_1$ = 52.12 $\pm$ 1.38 and $R_2$ = 67.63 $\pm$ 1.40 R$_\odot$ and their masses are $M_1$ = 4.914 $\pm$ 0.021 and $M_2$ = 4.875$\pm$ 0.021 M$_\odot$ . The exquisite accuracy of 0.5% obtained for the masses of the components is one of the best mass determinations for giants. We derived a precise distance to the system of 2.14 $\pm$ 0.06 kpc (stat.) $\pm$ 0.05 (syst.) which places the star in the Sagittarius-Carina arm. The Galactic rotational velocity of the star is $\Theta_s=258 \pm 26$ km s$^{-1}$ assuming $\Theta_0=238$ km s$^{-1}$. A comparison with PARSEC isochrones places the system at the early phase of core helium burning with an age of slightly larger than 100 million years. The effect of overshooting on stellar evolutionary tracks was explored using the MESA star code.

Outer rotation curve of the Galaxy with VERA. II. Annual parallax and proper motion of the star-forming region IRAS 21379+5106

Abstract We conducted astrometric very long baseline interferometry (VLBI) observations of water-vapor maser emission in the massive star-forming region IRAS 21379+5106 in order to measure the annual parallax and proper motion, using VLBI Exploration of Radio Astrometry (VERA). The annual parallax measured 0.262 ± 0.031 mas, corresponding to a distance of $3.82^{+0.51}_{-0.41}\:$kpc. The proper motion was (μαcos δ, μδ) = (−2.74 ± 0.08, −2.87 ± 0.18) mas yr−1. By using this result, the Galactic rotational velocity was estimated to be Vθ = 218 ± 19 km s−1 at the galactocentric distance R = 9.22 ± 0.43 kpc, when we adopted the Galactic constants R0 = 8.05 ± 0.45 kpc and V0 = 238 ± 14 km s−1. With the newly determined distance, the bolometric luminosity of the central young stellar object was reestimated to be (2.15 ± 0.54) × 103 L⊙, which corresponds to the spectral type of B2–B3. The maser features were found to be distributed along a straight line extending from the southwest to the northeast. In addition, a vector map of the internal motions, constructed from the residual proper motions, implies that the maser features trace a bipolar flow, and that it cannot be explained by simple ballistic motions.

The enigmatic He-sdB pulsator LS IV-14°116: new insights from the VLT

The intermediate Helium subdwarf B star LS IV$-$14$^\circ$116 is a unique object showing extremely peculiar atmospheric abundances as well as long-period pulsations that cannot be explained in terms of the usual opacity mechanism. One hypothesis invoked was that a strong magnetic field may be responsible. We discredit this possibility on the basis of FORS2 spectro-polarimetry, which allows us to rule out a mean longitudinal magnetic field down to 300 G. Using the same data, we derive the atmospheric parameters for LS IV$-$14$^\circ$116 to be $T_{\rm eff}$ = 35,150$\pm$111 K, $\log{g}$ = 5.88$\pm$0.02 and $\log{N(\rm He)/N(\rm H)}$ = $-$0.62$\pm$0.01. The high surface gravity in particular is at odds with the theory that LS IV$-$14$^\circ$116 has not yet settled onto the Helium Main Sequence, and that the pulsations are excited by an $\epsilon$ mechanism acting on the Helium-burning shells present after the main Helium flash. Archival UVES spectroscopy reveals LS IV$-$14$^\circ$116 to have a radial velocity of 149.1$\pm$2.1 km/s. Running a full kinematic analysis, we find that it is on a retrograde orbit around the Galactic centre, with a Galactic radial velocity component $U$=13.23$\pm$8.28 km/s and a Galactic rotational velocity component $V$=$-$55.56$\pm$22.13 km/s. This implies that LS IV$-$14$^\circ$116 belongs to the halo population, an intriguing discovery.

Dark galactic halos without dark matter

Using standard Einstein theory, baryonic mass cannot account for observed galactic rotation velocities and gravitational lensing, attributed to galactic dark-matter halos. In contrast, theory constrained by Weyl conformal scaling symmetry explains observed galactic rotation in the halo region without invoking dark matter. An explanation of dark halos, gravitational lensing, and structural stabilization, without dark matter and consistent with conformal theory, is proposed here. Condensation of uniform primordial matter into a material cloud or galaxy vacates a large surrounding spherical halo. Within such an extended vacancy in the original cosmic background mass-energy density, conformal theory predicts centripetal acceleration of the observed magnitude.

VLBI observations of H2O maser annual parallax and proper motion in IRAS 20143+3634: Reflection on the Galactic constants

Abstract We report the results of very long baseline interferometry (VLBI) observations of H2O masers in the IRAS 20143+3634 star-forming region (SFR) using VERA (VLBI Exploration of Radio Astrometry). By tracking masers for a period of over two years we measured a trigonometric parallax of π = 0.367 ± 0.037 mas, corresponding to a source distance of $D = 2.72 ^{+0.31}_{-0.25}$ kpc and placing it in the Local spiral arm. Our trigonometric distance is just 60% of the previous estimation based on radial velocity, significantly impacting the astrophysics of the source. We measured proper motions of −2.99 ± 0.16 mas yr−1 and −4.37 ± 0.43 mas yr−1 in RA and Dec, respectively, which were used to estimate the peculiar motion of the source as (Us, Vs, Ws) = (−0.9 ± 2.9, −8.5 ± 1.6, +8.0 ± 4.3) km s−1 for R0 = 8 kpc and Θ0 = 221 km s−1, and (Us, Vs, Ws) = (−1.0 ± 2.9, −9.3 ± 1.5, +8.0 ± 4.3) km s−1 for R0 = 8.5 kpc and Θ0 = 235 km s−1. IRAS 20143+3634 was found to be located near the tangent point in the Cygnus direction. Using our observations we derived the angular velocity of Galactic rotation of the local standard of rest (LSR), Ω0 = 27.3 ± 1.6 km s−1 kpc−1, which is consistent with previous values derived using VLBI astrometry of SFRs at the tangent points and Solar circle. It is higher than the value recommended by the International Astronomical Union of Ω0 = 25.9 km s−1 kpc−1 which was calculated using the Galactocentric distance of the Sun and circular velocity of the LSR.

Tully-Fisher relation, galactic rotation curves and dissipative mirror dark matter

If dark matter is dissipative then the distributionof dark matter within galactic halos can be governed by dissipation, heating and hydrostatic equilibrium.Previous work has shown that a specific model, in the framework of mirror dark matter, can explain several empirical galactic scaling relations. It is shown here that this dynamical halo model implies a quasi-isothermal dark matter density,ρ(r) ≃ ρ0r02/(r2+r02), wherethe core radius, r0, scales with disk scale length, rD, viar0/kpc ≈ 1.4(rD/kpc). Additionally, the product ρ0r0 is roughlyconstant, i.e. independent of galaxy size(the constant is set by the parameters of the model).The derived dark matter density profile implies that the galactic rotation velocity satisfies the Tully-Fisher relation,LB∝v3max, where vmax is the maximal rotational velocity.Examples of rotation curves resulting from this dynamics are given.

UCAC4: Stellar kinematics with vector spherical functions

AbstractWe present a method of kinematic analysis of proper motions by vector spherical functions, and the results of its application to astrometric data. The sets of vector spherical functions which are orthonormal on a full sphere as well as on a latitude zone are constructed. Decomposition of the proper motions into a set of such functions allows model‐independent study of stellar kinematics. If needed, the parameters of the standard (say, Ogorodnikov‐Milne) model may be derived from the coefficients of the decomposition. In contrast to the commonly used least squares estimation of the model's parameters, vector spherical functions identify all systematic components of the velocity field (no matter, whether they are incorporated into the model or not) and give us a possibility to test whether the data are compatible with the model. In this paper, we apply this technique for the first time to the proper motions from the UCAC4 catalog for stars in the 11 to 16 magnitude range. We derive all‐sky solutions and the solutions based on stars in the northern and southern Galactic hemispheres. The all‐sky solution provide evidence for noticeable magnitude‐dependent trends in the coordinates of the solar motion apex, Oort constants, angular speed of the local Galactic rotation, and the slope of the local rotation velocity curve as we go from bright to faint stars. Furthermore, our all‐sky vector spherical function analysis identified strong and reliable extramodel harmonics, whereas the solutions for the northern and southern hemisphere indicate sign reversals for some of the Ogorodnikov‐Milne parameters. We show that both effects appear simultaneously and can be explained by the slowdown of Galactic rotation with increasing distance from the main Galactic plane. We estimate the absolute value of the vertical gradient of the Galactic rotational velocity to be ∼40 km s–1 kpc–1. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A New Proposal for Galactic Dark Matter: Effect of f(T) Gravity

It is still a challenging problem to the theoretical physicists to know the exact nature of the galactic dark matter which causes the galactic rotational velocity to be more or less a constant. We have proposed that the dark matter as an effect of f(T) gravity. Assuming the flat rotation curves as input we have shown that f(T) gravity can explain galactic dynamics. Here, we don' have to introduce dark matter. Spacetime metric inspired by f(T) gravity describes the region up to which the tangential velocity of the test particle is constant. This inherent property appears to be enough to produce stable circular orbits as well as attractive gravity.

WAVELENGTH MEASUREMENTS OF K TRANSITIONS OF OXYGEN, NEON, AND MAGNESIUM WITH X-RAY ABSORPTION LINES

Accurate atomic transition data are important in many astronomical research areas especially in line spectroscopy study. Whereas transition data of He-like and H-like ions (i.e., ions at high-charge states) are accurately calculated, that of K transitions of neutral or low-ionized metal elements are still very uncertain. Spectroscopy of absorption lines produced in the interstellar medium (ISM) has been proven to be an effective way to measure the central wavelengths of these atomic transitions. In this work we analyze 36 Chandra High Energy Transmission Grating observations and search for and measure the ISM absorption lines along sight lines of 11 low-mass X-ray binaries. We correct the Galactic rotation velocity to the rest frame for every observation and then use two different methods to merge all the corrected spectra to a co-added spectrum. However the co-added spectra obtained by these methods exhibit biases, either to the observations of high counts or high signal-to-noise ratios of the lines. We make Bayesian analysis to several significantly detected lines to obtain the systematic uncertainty and the bias correction of other lines. Compared to previous studies (e.g., Yao et al. 2009), our results improve the accuracy of wavelengths by a factor from two to five and significantly reduce the systematic uncertainties and biases. Several weak transitions (e.g., 1s--2p of Mg IV and Mg V; 1s--3p of Mg III and Mg V) are also detected for the first time, albeit with low significance; future observations with improved accuracy are required to confirm these detections.

Estimation of the solar galactocentric distance and galactic rotation velocity from near-solar-circle objects

We have tested the method of determining the solar Galactocentric distance R_0 and Galactic rotation velocity $V_0$ modified by Sofue et al. using near-solar-circle objects. The motion of objects relative to the local standard of rest has been properly taken into account. We show that when such young objects as star-forming regions or Cepheids are analyzed, allowance for the perturbations produced by the Galactic spiral density wave improves the statistical significance of the estimates. The estimate of R_0=7.25\pm0.32 kpc has been obtained from 19 star-forming regions. The following estimates have been obtained from a sample of 14 Cepheids (with pulsation periods P>5^d): R_0=7.66\pm0.36 kpc and V_0=267\pm 17 km s^{-1}. We consider the influence of the adopted Oort constant A and the character of stellar proper motions (Hipparcos or UCAC4). The following estimates have been obtained from a sample of 18 Cepheids with stellar proper motions from the UCAC4 catalog: R_0=7.64\pm0.32 kpc and V_0=217\pm 11 km s^{-1}.

Induced energy polarization of the vacuum and the rotational curve for the Galaxy

The theory of an induced energy polarized vacuum, as previously presented by the author (Penner. Can. J. Phys. 90, 315 (2012)), is used to generate a theoretical rotational curve for the Galaxy. The theoretical curve generated is found to be in good agreement with Sofue's (Publ. Astron. Soc. Jpn. 64, (In press) (2012)) compilation of observations. For the baryonic mass distribution and baryonic Tully–Fisher relationship that is used, the theoretical orbital velocity at the Sun's location is found to be (235 ± 15) km s−1. The galactic rotational velocity is then found to slowly fall from this value as it asymptotically approaches the value of (192 ± 15) km s−1.

Conformal Gravity: Dark Matter and Dark Energy

This short review examines recent progress in understanding dark matter, dark energy, and galactic halos using theory that departs minimally from standard particle physics and cosmology. Strict conformal symmetry (local Weyl scaling covariance), postulated for all elementary massless fields, retains standard fermion and gauge boson theory but modifies Einstein–Hilbert general relativity and the Higgs scalar field model, with no new physical fields. Subgalactic phenomenology is retained. Without invoking dark matter, conformal gravity and a conformal Higgs model fit empirical data on galactic rotational velocities, galactic halos, and Hubble expansion including dark energy.

Fundamental Parameters of the Milky Way Galaxy Based on VLBI Astrometry

We present analyses to determine the fundamental parameters of the Galaxy based on VLBI astrometry of 52 Galactic maser sources obtained with VERA, VLBA, and EVN. We model the Galaxy's structure with a set of parameters, including the Galaxy center distance $ R_0$ , the angular rotation velocity at the LSR $ \Omega_0$ , the mean peculiar motion of the sources with respect to Galactic rotation ($ U_{\rm src}$ , $ V_{\rm src}$ , $ W_{\rm src}$ ), the rotation-curve shape index, and the $ V$ component of the Solar peculiar motions, $ V_\odot $ . Based on a Markov chain Monte-Carlo method, we find that the Galaxy center distance is constrained at a 5% level to be $ R_0$$ =$ 8.05 $ \pm$ 0.45 kpc, where the error bar includes both statistical and systematic errors. We also find that the two components of the source peculiar motion $ U_{\rm src}$ and $ W_{\rm src}$ are fairly small compared to the Galactic rotation velocity, being $ U_{\rm src}$$ =$ 1.0 $ \pm$ 1.5 km s$ ^{-1}$ and $ W_{\rm src}$$ =$$-$ 1.4 $ \pm$ 1.2 km s$ ^{-1}$ . Also, the rotation curve shape is found to be basically flat between Galacto-centric radii of 4 and 13 kpc. On the other hand, we find a linear relation between $ V_{\rm src}$ and $ V_\odot $ as $ V_{\rm src}$$ =$$ V_\odot $$-$ 19 ($ \pm$ 2) km s$ ^{-1}$ , suggesting that the value of $ V_{\rm src}$ is fully dependent on the adopted value of $ V_\odot $ . Regarding the rotation speed in the vicinity of the Sun, we also find a strong correlation between $ \Omega_0$ and $ V_\odot $ . We find that the angular velocity of the Sun, $ \Omega_{\odot}$ , which is defined as $ \Omega_\odot$$ \equiv$$ \Omega_0$$ +$$ V_\odot/R_0$ , can be well constrained with the best estimate of $ \Omega_\odot$$ =$ 31.09 $ \pm$ 0.78 km s$ ^{-1}$ kpc$ ^{-1}$ . This corresponds to $ \Theta_0$$ =$ 238 $ \pm$ 14 km s$ ^{-1}$ if one adopts the above value of $ R_0$ and recent determination of $ V_\odot $$ \sim$ 12 km s$ ^{-1}$.

ARCHEOLOGY OF AN ANCIENT STAR

We report on the bright and late F-type star HR 3138, which, with respect to its chemistry in the [Mg/H]-[Fe/Mg] abundance plane, we identify as an old Population II member. Evolutionary tracks are, however, in conflict with this finding and instead imply an age of only {tau} = 5.6{sup -1.8}{sub +{sub 2.2}} Gyr (2{sigma}) for HR 3138. We discuss this controversy in light of existing high-precision radial velocity surveys that mostly exclude the case of a blue straggler primary and a white dwarf secondary. While it is realized that a stellar merger can principally solve the issue and there is indeed observational evidence for mass accretion on HR 3138 from the absence of lithium in its photosphere, we also consider the interesting circumstance that HR 3138 lies in the direction to the 350 pc distant, young open cluster NGC 2516. We point to the possibility that the progenitor cloud of this cluster may likewise account for former mass accretion and we argue in particular for a dynamical friction with this cloud as a plausible cause for the strikingly common Galactic rotational velocity of the field star and open cluster.

Outer Rotation Curve of the Galaxy with VERA I: Trigonometric Parallax of IRAS 05168+3634

We report on a measurement of the trigonometric parallax of IRAS 05168$ +$ 3634 with VERA. The parallax is 0.532 $ \pm$ 0.053 mas, corresponding to a distance of 1.88$ ^{+0.21}_{-0.17}$ kpc. This result is significantly smaller than the previous distance estimate of 6 kpc, based on the kinematic distance. This drastic change in the source distance revises not only the physical parameters of IRAS 05168$ +$ 3634, but also its location of the source, placing it in the Perseus arm, rather than the Outer arm. We also measured the proper motions of the source. A combination of the distance and the proper motions with the systemic velocity yields a rotation velocity ($ \Theta$ ) of 227$ ^{+\ 9}_{-11}$ km s$ ^{-1}$ at the source, assuming $ \Theta_{\rm {0}}$$ =$ 240 km s$ ^{-1}$ . Our result combined with previous VLBI results for six sources in the Perseus arm indicates that the sources rotate systematically slower than the Galactic rotation velocity at the LSR. In fact, we show observed disk peculiar motions averaged over the seven sources in the Perseus arm as ($ U_{\rm {mean}}$ , $ V_{\rm {mean}}$ ) $ =$ (11 $ \pm$ 3, $-$ 17 $ \pm$ 3) km s$ ^{-1}$ , indicating that these seven sources are systematically moving toward the Galactic center, and lag behind the Galactic rotation.

The outer rotation curve project with VERA: Trigonometric parallax of IRAS 05168+3634

AbstractWe present a measurement of the trigonometric parallax of IRAS 05168+3634 with VERA. The parallax is 0.532 ± 0.053 milli-arcsec, corresponding to a distance of 1.88+0.21−0.17 kpc. This is significantly closer than the previous distance estimate of 6 kpc based on a kinematic distance measurement. This drastic change in the source distance implies the need for revised values of not only the physical parameters of IRAS 05168+3634, but it also impies a different location in the Galaxy, placing it in the Perseus arm rather than the Outer arm. We also measured the proper motion of the source. A combination of the distance and proper motion with the systemic velocity yields a rotation velocity Θ = 227+9−11 km s−1 at the source position, assuming Θ0 = 240 km s−1. Our result, combined with previous VLBI results for six sources in the Perseus arm, indicates that the sources rotate systematically more slowly than the Galactic rotation velocity at the local standard of rest. In fact, we derive peculiar motions in the disk averaged over the seven sources in the Perseus arm of (Umean, Vmean) = (11 ± 3, −17 ± 3) km s−1, which indicates that these seven sources are moving systematically toward the Galactic Center and lag behind the overall Galactic rotation.