No evidence for a dark matter disk within 4 kpc from the Galactic plane

We estimated the dynamical surface mass density (Sigma) at the solar Galactocentric distance between 2 and 4 kpc from the Galactic plane, as inferred from the observed kinematics of the thick disk. We find Sigma(z=2 kpc)=57.6+-5.8 Mo pc^-2, and it shows only a tiny increase in the z-range considered by our investigation. We compared our results with the expectations for the visible mass, adopting the most recent estimates in the literature for contributions of the Galactic stellar disk and interstellar medium, and proposed models of the dark matter distribution. Our results match the expectation for the visible mass alone, never differing from it by more than 0.8 $Mo pc^-2 at any z, and thus we find little evidence for any dark component. We assume that the dark halo could be undetectable with our method, but the dark disk, recently proposed as a natural expectation of the LambdaCDM models, should be detected. Given the good agreement with the visible mass alone, models including a dark disk are less likely, but within errors its existence cannot be excluded. In any case, these results put constraints on its properties: thinner models (scale height lower than 4 kpc) reconcile better with our results and, for any scale height, the lower-density models are preferred. We believe that successfully predicting the stellar thick disk properties and a dark disk in agreement with our observations could be a challenging theoretical task.Comment: Accepted for publication in ApJ Letter

Central Proper-Motion Kinematics of NGC 6752

We present proper motions derived from WFPC2 imaging for stars in the core of the peculiar globular cluster NGC 6752. The central velocity dispersion in both components of the proper motion is 12 km/s. We discuss the implications of this result as well as the intrinsic difficulties in making such measurements. We also give an alternative correction for the 34-row problem in the WFPC2 CCDs.Comment: 25 pages, 7 figures, 1 table included. Accepted for publication in A

Astrometry with the Hubble Space Telescope: Trigonometric Parallaxes of Selected Hyads

We present absolute parallaxes and proper motions for seven members of the Hyades open cluster, pre-selected to lie in the core of the cluster. Our data come from archival astrometric data from FGS 3, and newer data for 3 Hyads from FGS 1R, both white-light interferometers on the Hubble Space Telescope (HST). We obtain member parallaxes from six individual Fine Guidance Sensor (FGS) fields and use the field containing van Altena 622 and van Altena 627 (= HIP 21138) as an example. Proper motions, spectral classifications and VJHK photometry of the stars comprising the astrometric refer- ence frames provide spectrophotometric estimates of reference star absolute parallaxes. Introducing these into our model as observations with error, we determine absolute parallaxes for each Hyad. The parallax of vA 627 is significantly improved by including a perturbation orbit for this previously known spectroscopic binary, now an astrometric binary. Compared to our original (1997) determina- tions, a combination of new data, updated calibration, and improved analysis lowered the individual parallax errors by an average factor of 4.5. Comparing parallaxes of the four stars contained in the Hipparcos catalog, we obtain an average factor of 11 times improvement with the HST . With these new results, we also have better agreement with Hipparcos for the four stars in common. These new parallaxes provide an average distance for these seven members, = 47.5 pc, for the core a \pm 1 - {\sigma} dispersion depth of 3.6 pc, and a minimum depth from individual components of 16.0 \pm 0.9 pc. Absolute magnitudes for each member are compared to established main sequences, with excellent agreement. We obtain a weighted average distance modulus for the core of the Hyades of m-M=3.376 \pm 0.01, a value close to the previous Hipparcos values, m-M=3.33\pm 0.02.Comment: 21 pages, 7 figures, Astronomical Journal, accepted 2011-3-

Actualiteiten Varkensproefbedrijf Raalte

Op het Varkensproefbedrijf in Raalte wordt nieuw onderzoek opgestart bij vleesvarkens. Er is een opzet gemaakt voor een voeding- en een mestbehandelingsproef. - Onderzoek multifasenvoedering - Onderzoek microbieel aanzure

The Southern Proper Motion Program IV. The SPM4 Catalog

We present the fourth installment of the Yale/San Juan Southern Proper Motion Catalog, SPM4. The SPM4 contains absolute proper motions, celestial coordinates, and (B,V) photometry for over 103 million stars and galaxies between the south celestial pole and -20 deg declination. The catalog is roughly complete to V=17.5 and is based on photographic and CCD observations taken with the Yale Southern Observatory's double-astrograph at Cesco Observatory in El Leoncito, Argentina. The proper-motion precision, for well-measured stars, is estimated to be 2 to 3 mas/yr, depending on the type of second-epoch material. At the bright end, proper motions are on the International Celestial Reference System by way of Hipparcos Catalog stars, while the faint end is anchored to the inertial system using external galaxies. Systematic uncertainties in the absolute proper motions are on the order of 1 mas/yr.Comment: 34 pages, 8 figures, 3 tables; accepted for publication in AJ; note - modified author list and acknowledgements sectio

The Southern Proper Motion Program III. A Near-Complete Catalog to V=17.5

We present the third installment of the Yale/San Juan Southern Proper Motion Catalog, SPM3. Absolute proper motions, positions, and photographic B,V photometry are given for roughly 10.7 million objects, primarily stars, down to a magnitude of V=17.5. The Catalog covers an irregular area of 3700 square degrees, between the declinations of -20 and -45 degrees, excluding the Galactic plane. The proper-motion precision, for well-measured stars, is estimated to be 4.0 mas/yr. Unlike previous releases of the SPM Catalog, the proper motions are on the International Celestial Reference System by way of Hipparcos Catalog stars, and have an estimated systematic uncertainty of 0.4 mas/yr. The SPM3 Catalog is available via electronic transfer,(http://www.astro.yale.edu/astrom/) As an example of the potential of the SPM3 proper motions, we examine the Galactocentric velocities of a group of metal-poor, main-sequence A stars. The majority of these exhibit thick-disk kinematics, lending support to their interpretation as thick-disk blue stragglers, as opposed to being an accreted component.Comment: 23 pages, 10 figures, accepted for publication in Astronomical Journa

Huisvesting

Groepshuisvesting zeugen- Groepshuisvesting dragende zeugen- Groepshuisvesting in de kraamfase Combihok Vloeruitvoering hokken gespeende bigge

Observations of Binary Stars with the Differential Speckle Survey Instrument. V. Toward an Empirical Metal-Poor Mass-Luminosity Relation

In an effort to better understand the details of the stellar structure and evolution of metal poor stars, the Gemini North telescope was used on two occasions to take speckle imaging data of a sample of known spectroscopic binary stars and other nearby stars in order to search for and resolve close companions. The observations were obtained using the Differential Speckle Survey Instrument, which takes data in two filters simultaneously. The results presented here are of 90 observations of 23 systems in which one or more companions was detected, and 6 stars where no companion was detected to the limit of the camera capabilities at Gemini. In the case of the binary and multiple stars, these results are then further analyzed to make first orbit determinations in five cases, and orbit refinements in four other cases. Mass information is derived, and since the systems span a range in metallicity, a study is presented that compares our results with the expected trend in total mass as derived from the most recent Yale isochrones as a function of metal abundance. These data suggest that metal-poor main-sequence stars are less massive at a given color than their solar-metallicity analogues in a manner consistent with that predicted from the theory