Oort Constants Research Articles

The New Catalogue of Positions and Proper Motions of 5115 Bright Stars Compiled as the Result of the International “Bright Stars” Program

At Kyiv University Observatory, in accordance with IAU resolution, the Combined Catalogue of Positions and Proper Motions of 5115 Bright Stars in the FK5 system for Epoch and Equinox J2000.0 (BSC, see reference) has been compiled using 20 source catalogues obtained within the framework of ‘Bright Stars’ International Program. The source catalogs are Bordeaux-66, Bucharest-65, Bucharest-68, Belgrade-79, Cape-68, Kharkiv-70n, Kharkiv-70s, Kyiv-66, Kyiv-73, El Leoncito-70, Moscow-76, Mykolaiv-65, Perth-70, Perth-75, Santiago-65, Santiago-67, Strasbourg-65, Tashkent-64, Tokyo-68, Washington-66. The BSC accumulates around 30,000 source catalogue positions observed within 1960-1980. The standard errors of BSC do not exceed 0.1 arcsec and 0.25 arcsec/cy for positions and proper motions, respectively. The systematic differences between BSC and FK5 in positions for the mean BSC epoch 1970 as a rule do not exceed several hundredths of arcsec. A comparison of the BSC with the PPM catalogue indicates that in the latter the accuracy of positions and proper motions of the ordinary bright stars is slightly worse than that of average values given by the authors of the PPM. It is important to note that the comparison of the BSC with PPM for various star subsets shows deviations of both the HPS bright star system and the rest of the PPM bright stars, on the one hand, from the stars of the FK5 Extension contained in the PPM on the other hand. To examine the BSC proper motion system the stellar astronomy constants and correction to precession have been determined using the BSC proper motions. The parameters obtained agree with the standard ones. But the Oort constants are slightly smaller than those of standard.The BSC catalogue as a whole is acceptable for astrometry usage with respect to both accidental and systematic accuracy.

On the ellipticity of the Galactic disk

We investigate two kinds of constraints on the ellipticity of the Galactic disk: local constraints, based on the kinematics of the solar neighborhood (such as the Oort constants, the axis ratio of the velocity ellipsoid, the vertex deviation, and the radial velocity of the local standard of rest relative to the Galactic center), and global constraints (H I tangent point velocities, the velocity fields of distant carbon stars, Cepheids and H II regions, and the kinematics of distant H I). Local and global constraints independently suggest that the Sun lies near the minor axis of the potential of an elliptical Galactic disk, with equipotential axis ratio 0.9. The kinematic data are consistent with a flat rotation curve of constant ellipticity, with a mean rotation speed of 200 km/s. In this model, the present velocity of the local standard of rest is 180 km/s.

THE GOULD BELT: STRUCTURE AND ORIGIN

ABSTRACT The structure of the Gould Belt system of young stars and star formation complexes has been studied, mainly through the use of an extended sample of early-type stars. Statistical derivations of some of the most relevant parameters of the Belt (orientation, spatial extent, stellar content, age) are made, and some large scale trends of the recent history of star formation in the solar neighbourhood are discussed. Special attention is paid to the local kinematics of young objects; the local peculiar kinematics as revealed by anomalous values of Oort constants is fitted by an expansion of the local system along a preferential line, superimposed to the general pattern of galactic rotation. Some other regions with anomalous motions are detected outside the Gould Belt, with strong evidences for a moving group possibly related to the Cygnus Superbubble. Dynamics of the tilted plane containing the Belt implies a very constrained range of possible values for its original orientation. Moreover, indications of a vertical oscillating motion of the ensemble of stars in the Belt have been found, the association to the Belt being supported by the fact that both the oscillation axis and the current state of vertical motion relate well to the overall picture of the Gould Belt. A second part of this work is devoted to a theory on the origin of the Gould Belt. We propose it to have formed from the collision of a high velocity c loud on the galactic disk by the large scale phase transition of the galactic interstellar medium triggered by the colliding cloud. Analytic 1-D calculations provide us with the values of the most relevant quantities involved in the shock. 2-D computer simulations show the morphology of the region affected by the shock. The stability analysis of the shocked material shows that the unstable regions should have characteristics and locations similar to those of currently observed complexes belonging to the Gould Belt. The galactic magnetic field is essential in determining the further evolution of the shocked material. An overall agreement is found between the observation of structures belonging to the Belt and the predictions of our model.

Precession and Stellar Kinematic Parameters from the Proper Motions of the AGK3U

Precessional corrections and stellar kinematic parameters have been derived from the proper motions of 142,171 stars in the updated version of AGK3 (AGK3U). The sky has been divided into 1332 small areas, in which mean proper motions for each component are formed for different magnitude intervals, with and without exclusion of fast stars. Solutions were performed for various kinds of the mean proper motions. Maximum-likelihood algorithm is used to take into account the ellipsoidal distribution of residual velocities. The results for precessional correction are, Δn = 0″.47 ± 0″.03 /cy, Δk = −0″.35 ± 0″.02 /cy, and the results for Oort's constants are, A = 9.5 ± 1.5 km/s/pc, B = −7.5 ± 1.5 km/s/pc.

Is the Vorticity Vector of the Galaxy Perpendicular to the Galactic Plane?

The modern astrometric catalogue ACRS invites attempts to re-examine the systematic stellar motions, together with the luni-solar precessional correction and the fictitious equinoctial motion correction to the FK5 system, and gives encouraging results.On the basis of the three-dimensional Ogorodnikov-Milne model for the overall pattern analysis of the proper motions, the systematic stellar velocity field of about 30000 K-M giants chosen from the ACRS is first examined in the heliocentric distance interval 0.5 to 1.0 kpc. We have found in an iterative fashion a solution for the K-M giants that yields neither deformation-nor vorticity-field other than the classical ones (the Oort constants A and B). The important point to note here is that the generally accepted idea such that the K-M giants are a steady-state constituent of the galaxy is compatible with the luni-solar precessional correction proposed by the VLBI and LLR observations. The K-M giants give the rational set of corrections to the FK5 system: the luni-solar precessional correction Δp = −0″.27 ± 0″.03 / cent and the equinoctial motion correction including the planetary precessional correction Δe + Δλ = −0″.12 ± 0″.03 / cent. Thus, the precessional correction previously proposed with the modern techniques has been confirmed by the pattern analysis of the proper motions.Next, applying the corrections obtained above, we have performed the overall pattern analysis of the proper motions of about 3000 O-B5 stars, supergiants, and bright giants, which are chosen again from the ACRS, and considered as an entity of the galactic warp. It is found that the kinematics of these stars is quite different from that of K-M giants. These stars show additional shears and rotations around two mutually orthogonal axes lying in the galactic plane, besides the classical ones. The present finding implies that the young stars are streaming around the galactic center in a tilted sheet (the warp) with the velocity of 225 km/s, and the sheet itself is simultaneously rotating around the nodal line of the warp (galactic center — sun — anticenter line) with the angular velocity of 4 km/s/kpc in increasing sense of the present inclination of the warp.

Absolute magnitudes and kinematic properties of Cepheids

A maximum likelihood statistical parallax analysis of classical Cepheids has been performed to determine the relative solar motion, Oort constants, velocity ellipsoid parameters, and zero points of the PL and PLC relations. The analysis is based upon 90 proper motions drawn from the list of Karimova and Pavlovskaya and upon the analytical approach of Hawley et al. Our results give a best estimate for the mean absolute magnitude of Cepheids at log P=0.8 of =−3.46±0.33 mag. This estimate for the Cepheid absolute magnitude zero point is highly stable against refinements in the mathematical technique and against additional Cepheid proper motion data of quality similar to the existing proper motions

REINVESTIGATION OF O, B STAR KINEMATICS AND DETERMINATION OF CORRECTIONS TO PRECESSION

Radial velocities, distances and proper motions of 1412 early-type stars are used for in-vestigation and analysis of the galactic kinematics in the solar neighbourhood. It is shownfrom the results obtained here that differences among the components (uo, vo) of meanmotions relative to the Sun of early-type stars with different heliocentric distances are sig-nificant. This phenomenon can be reasonably explained by the three-star drift hypothesis,and thus the conventional Local Standard of Rest is likely to be moving outwards at 25 km/s.The Oort constants A and B and the parameters C and D connected with radial motion ofthe Galaxy that are obtained from the present investigation are (A, B)=(16.6±0.6, -14.4±1.7) km/s/kpe and (C, D)=(0.5±0.5, -2.0 ±0.4) km/s/kpe, respectively, which are invery satisfactory agreement with corresponding values of these parameters gained before. Thedetermined precession corrections, which are based on the kinematic parameters found fromsolution and data of fundamental proper motions of stars, are quite accurate: (△n, △k)=(0.″56 ± 0.″04, -0.″33 ± 0.″05) per century. The found △n, △k fully coincide with previouscorresponding values obtained by some authors.

The local complex of O and B stars. II - Kinematics

The observed space velocities of O-B5 stars lying within about 1 kpc of the sun are analyzed. Motions examined include local solar motion, differential galactic rotation, mean peculiar stellar velocities, and systematic stellar motions parallel and perpendicular to the galactic plane. Kinematical determinations of the Oort constant and the K term for stars previously classified as members of the Gould and galactic belts are found to confirm earlier results that the Gould belt (or at least its youngest component) comprises a local perturbation in the general galactic velocity field. It is shown that if the Gould belt is expanding as a unit, its expansion age must be about 70 million years. The analyses also indicate negligibly small translational motion of the Gould belt relative to the galactic belt and parallel to the galactic plane as well as an approximate 'seesaw' motion of the Gould belt about the Cassiopeia-Carina line in the galactic plane. The age of the Gould belt is inferred to be either 20 or 60 million years from the vertical motions, which would imply the existence of either one or two waves of star formation as the Gould belt passed through the galactic belt either once or twice.

A New Value for the Rotation Speed of the Spiral Structure

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.

A problem in distance-determination for Mira variables with an appendix on OB-star distances

Difficulties in accepting the results on the kinematics of distant Mira variables obtained by Smak and Preston (1965) and in paper II, are outlined. It is shown that proper allowance for statistical bias in the distance determinations together with an allowance for the different definition of maximum magnitude, as used in these two investigations and in the statistical parallax work, removes the difficulties. It appears that the values of the Oort constant ( A) for Mira variables do not contradict the predictions of ellipsoidal theory. It is estimated that a considerable number of the stars in paper II must lie in the vicinity of the galactic centre, where large rotational effects are found. The present investigation strengthens the previous conclusion that the velocity dispersion, radial from the galactic centre, is independent of the galactocentric distance for Miras of a given period. It is shown that the absolute magnitudes of the Miras derived from statistical parallaxes are in substantial agreement with those derived from clusters and visual binaries including a new determination from the companion to U Men. Statistical effects in the distance determinations for OB-type stars are discussed in the appendix in order to bring out differences between the treatment necessary in this case and in that of the Miras.

Generating mechanisms for spiral waves

To maintain the spiral structure over long periods in spite of the chaotic disturbances so often seen in galaxies it is probably necessary to have a large energy store which is gradually tapped to generate and maintain the spiral wave. Now in a sense stable axially symmetrical model galaxies are configurations of minimum energy for a given angular momentum structure. By a given angular momentum structure I mean that the function μ(h)dh giving the total mass with specific angular momentum between h and h + dh is given and in making the minimum energy statement I have assumed that there is sufficient ‘random’ motion to satisfy Toomre's local stability criterion. To tap a store of energy one must either tap the energy of the whole rotational structure by finding disturbances that may change μ(h), or one may tap the smaller energy store of the ‘random’ motions. Clearly the larger energy store is the more attractive. Now μ(h) is conserved for any axially symmetrical time dependent motions so the only disturbances that can change μ(h) are non-axially symmetrical. If one considers a single star moving in nearly circular motion and interacting with a weak disturbance in the gravitational potential which may be Fourier analysed into components of the form S(R) exp[i(mΦ+ωt)] then one finds that the energy and angular momentum of the star oscillate but do not change in the mean. This statement is untrue when the force due to the wave does not average to zero or when it resonates with the natural oscillation of the star about the circular motion. The angular frequency of the force seen by the star is ω + mΩ, where Ω(R) is the rotational angular velocity of the galaxy, so the exceptions occur at the resonances Here κ(R) = (4B(B-A))1/2, the epicyclic angular frequency, and A(R) and B(R) are Oort's constants. At the radius where ω + mΩ(R) = 0 the pattern of the disturbance moves around at the same velocity as the circular motion of the stars epicentre. The other resonances that were discovered by B. Lindblad lie one within and one outside that circle.

A New Determination of oort's Constant A from Cepheids

A New Determination of oort's Constant A from Cepheids

The Kinematics of B Stars, Cepheids, Galactic Clusters and Interstellar Gas in the Galaxy

An analysis has been made of B star motions using all available stars with reliable radial velocities and distances. The radial velocities of the interstellar Ca II lines have also been studied. Recent work on cepheids and galactic clusters is discussed and in part re-analysed. The principal results are the following: 1. The K -term for the B stars (Table I and Section 4) varies with distance from the Sun, probably due to the effects of large stellar groupings. This effect conceals any dependence on spectral type and luminosity class except for the O stars where a significant positive K -term is probably chiefly due to a gravitational red shift (Section 4 (vii)). 2. The values of the Oort constant A in varibus sub-groups of OB star spectral types and luminosity classes are in good agreement showing that the adopted absolute magnitude calibration is self-consistent. 3. The small percentage of high velocity B stars can have a considerable effect on the K -term. The velocity dispersions of B stars, cepheids and galactic clusters are all about the same (∼ 11.5 km/sec). That for the interstellar Ca II is somewhat lower (6.9 km/sec). The observed distributions of the residuals are generally gaussian. The effect on the dispersions of observational errors is discussed. It is unlikely that the true dispersion for B stars is less than about 9 km/sec. 4. The solar motion for B stars nearer than 0.25 kpc is appreciably different from that obtained from more distant stars. This is probably chiefly due to the effects of the Sco–Cen association. 5. The distances of the B stars are corrected statistically for systematic errors (Section 8 and Appendix). The ω ( R ) curve for B stars and interstellar Ca II is then in much better agreement with the 21 cm observations than the uncorrected ω ( R ) curve. However the optical results suggest that the Leiden ω ( R ) curve has been drawn too high (Section 13). 6. The best values found for the components of the solar motion and the Oort constant are u0 = + 10 km/sec, v0 = + 13 km/sec, ( w0 = + 6 km/sec adopted) and A = + 14.3 ± 0.8 km/sec/kpc. 7. Distant B stars are used to derive a value of R0 , the distance to the galactic centre of 9.9 ± 0.9 kpc.

Kinematics of the Mira Variables.

view Abstract Citations (35) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Kinematics of the Mira Variables. Smak, Jozef I. ; Preston, George W. Abstract Radial velocities based on Lick 120-inch coude spectrograms are given for 270 Mira variables previously unobserved for radial velocity. The great majority of these Miras have magnitudes in the interval 10 < mpe < 15. These observations are combined with those of Merrill and Feast to discuss the kinematic properties of the Miras. Distances are calculated by means of the absolute magnitudes of Osvalds and Risley and an exponential layer model of the interstellar extinction. Three values of the interstellar extinction coefficient were assumed:1 5, 2 0, and 2.5 pg. mag kpc-1 Values of the Oort constant A 15 km kpc-2 are obtained for period groups with F <350 days. A much larger value A 25 km kpc-2 is obtained for Miras with F > 350 days. The mean 0-component of the galactocentric motion for Miras decreases with increasing height above the galactic plane. This decrease is interpreted in terms of the ellipsoidal hypothesis and leads to z-dependent expressions for V0, A, and R , the galactocentric distance for which V0 is a maximum. Publication: The Astrophysical Journal Pub Date: October 1965 DOI: 10.1086/148364 Bibcode: 1965ApJ...142..943S full text sources ADS | data products SIMBAD (282)

Preliminary Results of Observations of Faint B Stars.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Preliminary Results of Observations of Faint B Stars. Petrie, R. M. Abstract Radial velocities, spectroscopic absolute magnitudes, and distances are available for nearly 500 B stars. These data are analyzed to determine the parameters of galactic motion. The results are preliminary in that some 200 stars are yet to be added to the sample when accurate magnitudes and colors become available. The following results are obtained: (1) There does not appear to be a close spatial connection between the distributions of the stars and the densest hydrogen clouds; (2) Circular galactic motion is the dominant feature and Oort's constant A is 20 km/sec/kpc; (3) A small outward radial motion is suggested by the behavior of the K term but the evidence is not conclusive; (4) Strong local departures from the circular motion are found, the most conspicuous one being in the direction of Perseus at a distance of 3 kpc. Publication: The Astronomical Journal Pub Date: September 1963 DOI: 10.1086/109104 Bibcode: 1963AJ.....68R.289P full text sources ADS |

Kinematical Analysis of the Cepheid Variables.

view Abstract Citations (3) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Kinematical Analysis of the Cepheid Variables. Takase, Bunshiro Abstract The selected 130 Cepheid K term K (km/sec) Sun's distance R0 (kpc) Zero-point correction ~M (mag.) Angular rotational ~ (R0) (km/sec kpc) velocity and its 1st w'(R0) (km/sec kpc2) and 2nd derivatives w" (R1) (km/sec kpc3) Oort's constant A (km/sec kpc) Solar motion S (km/sec) Apex in galactic L"0 (deg) coordinates B011 (deg) variables which have accurate photometric data and also the radial velocity and/or proper motion data were used to determine a consistent set of values concerning the galactic distance scale, the galactic rotation, and the local stellar motion. We solve the equations which express the relations between the observed motion, the solar motion, the differential galactic rotation, the peculiar motion, and other systematic motions, under the condition that the expectation of the peculiar motions is zero. Distances of the Cepheids were calculated using the period-luminosity relation and the period-color relation recently established by Kraft (Kraft, R. P., Astrophys. J. 134, 616, 1961). Thus we obtain the solar motion, the differential galactic rotation, the K term, and so on. We tried two kinds of solutions, one of which includes K term and the other of which does not. Calculations were also made for several R0 values, the distance of the sun from the galactic center, and for cases where the various zero-point corrections, AM, to the Kraft's period-luminosity relation were applied. The table shows results for cases selected from many others because of the reason that they give the A R0 values, where A is the Oort constant, closest to 156 km/sec determined by Schmidt (Schmidt, M., Bull. Astron. Inst. Neth. 13,15,1956) from the 21-cm radio observation. Since the photometric data of the Cepheids have been more accurately determined than their velocity data, it seems better to adopt the cases where no zero-point corrections were applied. Publication: The Astronomical Journal Pub Date: March 1963 DOI: 10.1086/108919 Bibcode: 1963AJ.....68...80T full text sources ADS |

Galactic Rotation Determined from Radial Velocities and Photometric Distances of Galactic Clusters.

view Abstract Citations (29) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Galactic Rotation Determined from Radial Velocities and Photometric Distances of Galactic Clusters. Johnson, H. L. ; Svolopoulos, S. N. Abstract A total of 36 galactic clusters whose photometrically determined distances are greater than 700 parse s, has radial velocities available. From an analysis of the radial velocities and distances of these cluster 1- together with the 21-cm radio data, a value of Oort's constant, A, of 15 km/sec/kpc is obtained. A con is parison of the radio data with the optical data indicates that the distance to the galactic center, R0, smaller than 10 kpc Publication: The Astrophysical Journal Pub Date: November 1961 DOI: 10.1086/147214 Bibcode: 1961ApJ...134..868J full text sources ADS |

On the Rotation of the Inner Parts of the Galactic System.

view Abstract Citations (18) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Rotation of the Inner Parts of the Galactic System. Münch, Guido ; Münch, Luis Abstract Results of radial-velocity measurements for 18 distant OB stars in galactic longitudes between 345 and 35 are presented. On the basis of published spectroscopic distance moduli, the results have been interpreted in terms of rotational velocities around the galactic center and compared with those of the interstellar neutral hydrogen. The stellar motions seem to suggest for the rotational velocity of the galactic system, at a distance of 6 kpc from the center, a value 10 km/sec higher than that indicated by the 21-cm line. At a distance of 4 kpc from the center, the stellar motions provide rotational velocities around 25 km/sec lower than the 21-cm line profiles do. This discrepancy is shown to be unlikely to arise from systematic errors in the spectroscopic distance moduli or in the radial velocities. The motion of the stars considered indicates a value for Oort's constant A somewhat larger than the classical value A = 20 km/sec. The BO.S Ia star HD 173438 has been found to be a single-line spectroscopic binary with a 250- day period, a semiamplitude of 50 km/sec, and an eccentricity of 0.54. Publication: The Astrophysical Journal Pub Date: March 1960 DOI: 10.1086/146830 Bibcode: 1960ApJ...131..253M full text sources ADS | data products SIMBAD (18)

On rotating ring orbits in galaxies

If ω is the angular velocity of circular motions in a stellar system depending on the distance R from the centre, and κ is the frequency of oscillation in the radius vector for an orbit in the equatorial plane which differs slightly from a circular orbit, we may show that in a coordinate system of angular speed the orbit in question is a closed oval, in the first approximation an ellipse, with two opposite vertices and with its centre in the centre of the system. The conditions are illustrated in Fig. 1, when AA is the apsidal line of an orbit. The expression for κ is where A is Oort's constant of differential rotation. If the distribution of matter in the stellar system may be approximated by a sum of concentric spheroids with one and the same plane of symmetry, the density increasing with decreasing dimensions of the spheroids, we should expect κ = 2ω close to the centre, whereas in the outermost regions we must expect that κ approaches to ω. It is therefore likely that ω – ½κ does not change appreciably within the system. Fig. 2 gives the run of κ, ω, and ω – ½κ for the galactic system according to the values of ω given by Kwee, Muller, and Westerhout [2]. In this case ω – ½κ changes very slowly with R. A relative orbit has a quite important property, if ω – ½κ is constant in the interval of R covered by the orbit. In this case, if the centre of gravity of a cloud of free particles follows the orbit, and if the velocity dispersion is small, the particles will pursue orbits which differ only slightly from each other and from the central orbit, but on the other hand there will in general be considerable differential motions along the central orbit. This orbit is therefore the curve in space along which a cloud of free particles tends to disperse. The process is similar to the dispersion of the meteoric particles of a comet along its orbit.

Values of Oort's constant A derived from some B stars

Values of Oort's constant A derived from some B stars