Galactic Kinematics Research Articles

The promise of Gaia and how it will influence stellar ages

AbstractThe Gaia space project, planned for launch in 2011, is one of the ESA cornerstone missions, and will provide astrometric, photometric and spectroscopic data of very high quality for about one billion stars brighter than V = 20. This will allow to reach an unprecedented level of information and knowledge on several of the most fundamental astrophysical issues, such as mapping of the Milky Way, stellar physics (classification and parameterization), Galactic kinematics and dynamics, study of the resolved stellar populations in the Local Group, distance scale and age of the Universe, dark matter distribution (potential tracers), reference frame (quasars, astrometry), planet detection, fundamental physics, Solar physics, Solar system science.I will present a description of the instrument and its main characteristics, and discuss a few specific science cases where Gaia data promise to contribute fundamental improvement within the scope of this Symposium.

Diffuse interstellar bands in RAVE survey spectra

We have used spectra of hot stars from the RAVE Survey in order to investigate the visibility and properties of five diffuse interstellar bands previously reported in the literature. The RAVE spectroscopic survey for Galactic structure and kinematics records CCD spectra covering the 8400–8800 A wavelength region at 7500 resolving power. The spectra are obtained with the UK Schmidt at the AAO, equipped with the 6dF multi-fiber positioner. The DIB at 8620.4 A is by far the strongest and cleanest of all DIBs occurring within the RAVE wavelength range, with no interference by underlying absorption stellar lines in hot stars. It correlates so tightly with reddening that it turns out to be a reliable tool to measure it, following the relation EB−V = 2.72(±0.03) × EW (A), valid throughout the general interstellar medium of our Galaxy. The presence of a DIB at 8648 A is confirmed. Its intensity appears unrelated to reddening, in agreement with scanty and preliminary reports available in the literature, and its measurability is strongly compromised by severe blending with underlying stellar He I doublet at 8649 A. The two weak DIBs at 8531 and 8572 A do not appear real and should actually be blends of underlying stellar lines. The very weak DIB at 8439 A cannot be resolved within the profile of the much stronger underlying hydrogen Paschen 18 stellar line.

Populating the Galaxy with pulsars I. Stellar and binary evolution

The computation of theoretical pulsar populations has been a major component of pulsar studies since the 1970s. However, the majority of pulsar population synthesis has only regarded isolated pulsar evolution. Those that have examined pulsar evolution within binary systems tend to either treat binary evolution poorly or evolve the pulsar population in an ad hoc manner. Thus, no complete and direct comparison with observations of the pulsar population within the Galactic disc has been possible to date. Described here is the first component of what will be a complete synthetic pulsar population survey code. This component is used to evolve both isolated and binary pulsars. Synthetic observational surveys can then be performed on this population for a variety of radio telescopes. The final tool used for completing this work will be a code comprised of three components: stellar/binary evolution, Galactic kinematics and survey selection effects. Results provided here support the need for further (apparent) pulsar magnetic field decay during accretion, while they conversely suggest the need for a re-evaluation of the assumed typical millisecond pulsar formation process. Results also focus on reproducing the observed P u P diagram for Galactic pulsars and how this precludes short time-scales for standard pulsar exponential magnetic field decay. Finally, comparisons of bulk pulsar population characteristics are made to observations displaying the predictive power of this code, while we also show that under standard binary evolutionary assumption binary pulsars may accrete much mass.

What will Gaia tell us about the Galactic disk?

AbstractGaia will provide parallaxes and proper motions with accuracy ranging from 10 to 1000 microarcsecond on up to one billion stars. Most of these will be disk stars: for an unreddened K giant at 6 kpc, it will measure the distance accurate to 2% and the transverse velocity to an accuracy of about 1 km/s. Gaia will observe tracers of Galactic structure, kinematics, star formation and chemical evolution across the whole HR diagram, including Cepheids, RR Lyrae, white dwarfs, F dwarfs and HB stars. Onboard low resolution spectrophotometry will permit – in addition to an effective temperature estimate – dwarf/giant discrimination, metallicity measurement and extinction determination. For the first time, then, Gaia will provide us with a three-dimensional spatial/properties map and at least a two-dimensional velocity map of these tracers. (3D velocities will be obatined for the brighter sources from the onboard RV spectrograph). This will be a goldmine of information from which to learn about the origin and evolution of the Galactic disk. I briefly review the Gaia mission, and then show how the expected astrometric accuracies translate into distance and velocity accuracies and statistics. I then briefly examine the impact Gaia should have on a few scientific areas relevant to the Galactic disk, specifically disk structure and formation, the age–metallicity–velocity relation, the mass–luminosity relation, stellar clusters and spiral structure. Concerning spiral arms, I note how a better determination of their locations and pattern speed from their OB star population, plus a better reconstruction of the Sun's orbit over the past billion years (from integration through the Gaia-measured gravitational potential) will allow us to assess the possible role of spiral arm crossings in ice ages and mass extinctions on the Earth.

Galactic kinematics with RAVE data

Galactic kinematics with RAVE data

Galactic kinematics near the sun from open clusters

AbstractA catalogue of open clusters is used to analyze the Galactic kinematics near the Sun. The Galactic open clusters, which are components of Galactic thin disk, were selected for our analysis. Based on kinematical data for around 270 Galactic open clusters, we found the Galactic rotation curve remains flat near the Sun. We also found Ve = 6.40±3.39 km s−1 inside the solar circle, which shows a weak trend of stars moving toward the Galactic anti-center.

Validation of the new Hipparcos reduction

Context.A new reduction of the astrometric data as produced by the Hipparcos mission has been published, claiming accuracies for nearly all stars brighter than magnitude Hp = 8 to be better, by up to a factor 4, than in the original catalogue. Aims.The new Hipparcos astrometric catalogue is checked for the quality of the data and the consistency of the formal errors as well as the possible presence of error correlations. The differences with the earlier publication are explained. Methods. The internal errors are followed through the reduction process, and the external errors are investigated on the basis of a comparison with radio observations of a small selection of stars, and the distribution of negative parallaxes. Error correlation levels are investigated and the reduction by more than a factor 10 as obtained in the new catalogue is explained. Results.The formal errors on the parallaxes for the new catalogue are confirmed. The presence of a small amount of additional noise, though unlikely, cannot be ruled out. Conclusions. The new reduction of the Hipparcos astrometric data provides an improvement by a factor 2.2 in the total weight compared to the catalogue published in 1997, and provides much improved data for a wide range of studies on stellar luminosities and local galactic kinematics.

Spectroscopic and light curve characterization of bulge microlensing events

Aims. Microlensing events have been observed regularly by surveys such as MACHO, OGLE and MOA. They offer an excellent way to probe the galactic structure, kinematics and stellar content. We have undertaken a follow-up study of 16 galactic microlensing events to determine masses and locations of the sources of these events within the Galaxy. Methods. Spectroscopy allows us to obtain information about the sources of the events. Low resolution spectra obtained with the Magellan I and II telescopes were analyzed to obtain radial velocities, spectral type and extinction by the method of Kane & Sahu. We also present results for the lens of the event using the microlensing light curve when possible. Light curves have been analyzed with the standard and the parallax models. Results. We have inferred a configuration inside our galaxy for each event, and therefore a lens mass estimation using a suitable galaxy model. Lens mass determination in some cases shows massive lenses that can be considered black hole candidates. This is the case for the events MACHO-98-BLG-6, and OGLE-00-BUL-43. In our sample only three events do not have enough parallax signal for a successful estimation of the lens mass.

STUDIES OF GALACTIC CEPHEIDS: THE INASAN/SAI INTEGRATED PROGRAM

We present the review of the main results of more than two decades of the Moscow program of Cepheid studies, carried out at the Institute of Astronomy (INASAN) and Sternberg Astronomical Institute (SAI). This program consists of extensive photometry and radial velocity measurements (the contribution from our team being the largest among observations of comparable precision), studies of period variations (permitting identification of the number of a particular star’s current instability-strip crossing), detection of spectroscopic binaries among Cepheids, determinations of Cepheid radii, discoveries of double-mode Cepheids, studies of galactic structure, kinematics, and dynamics, etc.

Galactic Kinematics from Open Clusters

On the basis of the astrophysical parameters of the Galactic open clusters published in the recent years, we have selected ~300 clusters completely with all measurements of their kinematical parameters. Almost all the clusters have a heliocentric distance less than 3.0 kpc. Inspecting the velocity field defined by the sample, we found some 30 clusters that have extremely large peculiar motions. All the clusters with large peculiar velocities are distant objects further than 2 kpc from the Sun, and some of them have large Galactic height |z|>0.35 kpc. The age ranges of the clusters are from 4 Myr to 1 Gyr with the intermediate age of 50 Myr.

Distances and Galactic Kinematics of Two Blue Metal‐poor Stars

ABSTRACTWe use an SX Phe period‐luminosity relation to derive distance estimates and Galactic kinematic parameters for the short‐period pulsating blue metal‐poor stars CS 29499−057 and CS 22966−043. The resulting kinematics are quite distinctive relative to the metal‐poor halo field. Even though these two field blue stragglers’ binarity is consistent with the idea of formation in a mass transfer system, we speculate that these stars’ origin instead lies in a Galactic merger or interaction with a dwarf galaxy satellite, or in the merger of a stellar binary system. The former possibility is consistent with CS 22966−043’s significant [α/Fe] deficiency. A non–mass‐transfer origin for both binaries is also consistent with (though not necessarily precluded by) the lack of any significant s‐process enhancement seen in either star, and the long orbital period of CS 29499−057 that may preclude a mass transfer origin. In an effort to determine distances to additional blue metal‐poor stars, we have photometrically monitored CS 22890−069, CS 22872−062, and CS 22884−065. However, the light curves of these three objects indicate no short‐period photometric variability at the level of a few hundredths of a magnitude.

On the distance, reddening and progenitor of V838 Mon

Extensive optical and infrared photometry as well as low and high resolution spectroscopy are used as inputs in deriving robust estimates of the reddening, distance and nature of the progenitor of V838 Mon, the 2002 outbursting event that produced a most spectacular light-echo. The reddening affecting V838 Mon is found to obey the RV = 3.1 law and amounts to (i) EB−V = 0.86 from the interstellar NaI and KI lines; (ii) EB−V = 0.88 from the energy distribution of the B3 V component; and (iii) EB−V = 0.87 from the progression of extinction along the line of sight. The adopted EB−V = 0.87 ± 0.01 is also the amount required by fitting the progenitor with theoretical isochrones of appropriate metallicity. The distance is estimated from (a) the galactic kinematics of the three components of the interstellar lines; (b) the amount of extinction vs. the HI column density and vs. the dust emission through the whole Galaxy in that direction; from (c) spectrophotometric parallax to the B3 V companion; from (d) comparison of the observed color−magnitude diagram of field stars with 3D stellar population models of the Galaxy; from (e) comparison of theoretical isochrones with the components of the binary system in quiescence and found to be around 10 kpc. Pre-outburst optical and IR energy distributions show that the component erupting in 2002 was brighter and hotter than the B3 V companion. The best fit is obtained for a 50 000 K source, 0.5 mag brighter than the B3 V companion. The latter passed unaffected through the outburst, which implies an orbital separation wide enough to avoid mass exchange during the evolution of the binary system, and to allow a safe comparison with theoretical isochrones for single stars. Such a comparison suggests that the progenitor of the outbursting component had an initial mass ∼65 M� ,t hat it was approaching the carbon ignition stage in its core at the time it erupted in 2002 and that the age of the V838 Mon binary system is close to 4 million yr. The 2002 event is probably just a shell thermonuclear event in the outer envelope of the star.

The nearest cool white dwarf (d$\mathsf{\sim4}$ pc), the coolest M-type subdwarf (sdM9.5), and other high proper motion discoveries

We report the discovery of seven high proper motion stars with proper motions between about 0.7 and 2.2 arcsec/yr, all at relatively low Galactic latitudes () and located in the southern sky. They were detected in a high proper motion search using multi-epoch positions in the optical SuperCOSMOS Sky Surveys and in the near-infrared sky surveys 2MASS and DENIS. Classification spectroscopy carried out for six of the objects reveals them to represent three different classes of cool objects in the solar neighbourhood: M dwarfs, M subdwarfs and cool white dwarfs. The star with the largest proper motion, SSSPM J1138–7722, is classified as a very nearby ( 8 pc) M 5.5 dwarf with Galactic thin disk kinematics. A second star with ~2 arcsec/yr proper motion, SSSPM J1358–3938, is still lacking spectroscopic confirmation but can be classified from photometry as a thick disk ~M 3.5 dwarf. Three objects turn out to be cool subdwarf members of the Galactic thick disk or halo, including the first sdM9.5 object, SSSPM J1013–1356, which represents the currently coolest known M subdwarf, another ultra-cool subdwarf, SSSPM J1930–4311, of spectral type sdM7.0 as well as an earlier type (sdM1.5) star. The latter, SSSPM J1530–8146, has an extremely large space velocity with clear halo kinematics (heliocentric km s-1). Two objects show featureless spectra classifying them as cool white dwarfs with K. One of them, SSSPM J1549–3544, is an extremely nearby ( pc) thin disk object, the other one, SSSPM J1148–7458, has thick disk kinematics. SSSPM J1549–3544 is likely to be the nearest cool white dwarf and may be even the nearest isolated white dwarf, i.e. closer than van Maanen 2.

Lick Northern Proper Motion Program. III. Lick NPM2 Catalog

The Lick Northern Proper Motion (NPM) program, a two-epoch (1947-1988) photographic survey of the northern two-thirds of the sky (Dec. > -23 deg), has measured absolute proper motions, on an inertial system defined by distant galaxies, for 380,000 stars from 8 14) anonymous stars for astrometry and galactic studies, 92,000 bright (B < 14) positional reference stars, and 35,000 special stars chosen for astrophysical interest. The NPM2 proper motions are on the ICRS system, via Tycho-2 stars, to an accuracy of 0.5 mas/yr in each field. RMS proper motion precision is 6 mas/yr. Positional errors average 80 mas at the mean plate epoch 1968, and 200 mas at the NPM2 catalog epoch 2000. NPM2 photographic photometry errors average 0.18 mag in B, and 0.20 mag in B-V. The NPM2 Catalog and the updated (to J2000) NPM1 Catalog are available at the CDS Strasbourg data center and on the NPM WWW site (this http URL). The NPM2 Catalog completes the Lick Northern Proper Motion program after a half-century of work by three generations of Lick Observatory astronomers. The NPM Catalogs will serve as a database for research in galactic structure, stellar kinematics, and astrometry.

The Universality of Turbulence in the Molecular Interstellar Medium and Its Exploitation as a Distance Estimator

The turbulent energy spectrum of molecular clouds in a variety of environments is measured via principal component analysis (PCA) of spectral line imaging observations at millimeter wavelengths. Molecular clouds with known distances have been previously shown to accurately obey a universal scale dependence of turbulent velocity dispersion over spatial scales of 1-50 pc, via both standard object-based analysis and, more recently, PCA. The PCA-based spectrum is accurately obeyed such that it may be used as a distance estimator for molecular clouds with ~30% accuracy, where the error budget is contributed to strongly by input H II region distances used for the calibration. The use of 13CO spectral line data for distance estimation is examined and compared to the distance calibration established for 12CO observations. We show that distances estimated using 13CO are in good agreement with those obtained using 12CO, with a possible ~10% distance overestimation for 13CO relative to the 12CO calibration. Several molecular clouds with known distances are subjected to PCA, and we demonstrate that the universal spectrum is closely respected by all clouds; PCA-based distances estimated under the assumption of exact adherence to the universal spectrum are derived and are shown to be in excellent agreement with optically estimated distances. We examine the possibility that the PCA distance estimation method may be used to solve the kinematic distance ambiguity in the inner Galaxy. We establish how PCA may be used to diagnose severe blending of near/far emission and, in cases of little or no blending, to accurately establish the near or far distance. The inner Galaxy results provide initial support for the global validity of the universal PCA spectrum previously demonstrated for the outer Galaxy only. In conjunction with the accurate velocity information provided by millimeter wavelength spectral line data, PCA can provide useful information for studies of Galactic structure and kinematics.

An extension of Herschel's method for dense and extensive catalogues

We present a way of handling and interpreting stellar proper motions, in which the idea of substituting them by great circles, proposed by Herschel in 1783, allows us to take the entire celestial sphere as a field of application, making possible the study of dense and extensive stellar zones. A suitable mathematical processing of data together with Herschel's method make up a good tool in order to search for and detect associations, clusters, systematic patterns of motion and to go deeper in the local galactic kinematic. In this paper, we explain our vision of Herschel's method, illustrating it with some practical examples. The particular case of solar motion is developed in a specific and complete way, using the whole Hipparcos catalogue, Herschel's method and our own mathematical tool, originally designed to determine systematic trends in plates or between catalogues. The solar apex and velocity obtained here are expressed as a continuous function, depending on the distribution of the stellar spectral types.

Kinematics of OB Stars

The kinematics of 1817 stars of class O-B5 are examined. The 1655 stars with distances up to 1 kpc are taken from the Hipparcos catalog and 162 stars with distances greater than 1 kpc from Westlin's study of OB stars. The Ogorodnikov-Milne model of Galactic kinematics, with Edmondson's second-order terms included, is used for the equations of condition and mixed total least squares-least squares (TLS-LS) is used for the reduction method. Reasonable values for the parameters of Galactic kinematics are obtained. In particular, Oort A and B constants yield a Galactic rotation of 258.7 ± 34.29 km s-1 if we take the distance of the Sun from the Galactic center as 8.5 ± 1.1 kpc. Although lower than the higher values obtained by some other investigators and higher than the IAU's recommended 220 ± 20 km s-1, all the determinations fall with their stated mean errors. Thus, no evidence for a significant difference in the various determinations exists. Evidence does exist, however, to assert that the TLS-LS reduction model with second-order terms seems superior to ordinary least-squares with only first-order terms.

Contribution of hipparcos to the determination of precession

The IAU (1976) luni-solar precession constant was derived by Fricke from intensive study of the catalog of 512 FK4-FK4/Sup distant stars. At present, when the data from the catalog HIPPARCOS is available, it is helpful to reconsider Fricke's analysis. This paper presents a redetermination of precession based on the following new factors: (a) the accurate parallaxes of stars have been taken into account; (b) galactic rotation and other kinematics have been eliminated from the proper motions of 512 stars; (c) the systems of the FK5 and improved GC catalog were used in combination with the HIPPARCOS catalog; (d) a new method (the MOTOR) of studying stellar kinematics was used. This method is based on the decomposition of proper motions on a set of orthogonal functions. The MOTOR, in contrast to the commonly used Least Squares Procedure, provides a test for whether or not the model is compatible with the data. Derived corrections to the IAU (1976) luni-solar precession constant are consistent with the results...

Kinematics of young stars

The young star velocity field is analysed by means of a galactic model which takes into account solar motion, differential galactic rotation and spiral arm kinematics. We use two samples of Hipparcos data, one containing O- and B-type stars and another one composed of Cepheid variable stars. The robustness of our method is tested through careful kinematic simulations. Our results show a galactic rotation curve with a classical value of A Oort constant for the O and B star sample (-13.8 km s-1 kpc-1) and a higher value for Cepheids (-16.9 km s-1 kpc-1, depending on the cosmic distance scale chosen). The second-order term is found to be small, compatible with a zero value. The study of the residuals shows the need for a K-term up to a heliocentric distance of 4 kpc, obtaining a value (1-3) km s-1 kpc-1. The results obtained for the spiral structure from O and B stars and Cepheids show good agreement. The Sun is located relatively near the minimum of the spiral perturbation potential (-20°) and very near the corotation circle. The angular rotation velocity of the spiral pattern was found to be km s-1 kpc-1.

Systematic Spectroscopic Observations on Small Telescopes: Past and Future Research of Stellar Kinematics

AbstractWe have used a CORAVEL-type spectrometer on small telescopes (70-cm, Moscow observatory, Russia; 60- and 100-cm, Simeiz observatory, Crimea, Ukraine and some others) for systematic observations of northern sky stars, since 1987 (Rastorguev &amp; Glushkova, 1997; Gorynya et al., 1998). The typical accuracy of a single measurement is about 0.5 km/s. The limiting magnitude is 14 in V-band. The young Galaxy disk population, metal-poor stars and Kaptein selected areas are the important parts of our program. In this paper we present new results on galactic kinematics and our future program.