75 research outputs found
Membership in the Young Cluster Trumpler 37
Astrometric positions for 1387 stars and proper motions for a subset of 1135 stars brighter than V=15 in a 1.5 degree surrounding the young open cluster Trumpler 37 are presented. Membership probabilities are presented for those stars with measured proper motions, and 486 stars with probabilities of \u3e80% are identified
Observations of Binary Stars with the Differential Speckle Survey Instrument. III. Measures below the Diffraction Limit of the WIYN Telescope
In this paper, we study the ability of CCD- and electron-multiplying-CCD-based speckle imaging to obtain reliable astrometry and photometry of binary stars below the diffraction limit of the WIYN 3.5 m Telescope. We present a total of 120 measures of binary stars, 75 of which are below the diffraction limit. The measures are divided into two groups that have different measurement accuracy and precision. The first group is composed of standard speckle observations, that is, a sequence of speckle images taken in a single filter, while the second group consists of paired observations where the two observations are taken on the same observing run and in different filters. The more recent paired observations were taken simultaneously with the Differential Speckle Survey Instrument, which is a two-channel speckle imaging system. In comparing our results to the ephemeris positions of binaries with known orbits, we find that paired observations provide the opportunity to identify cases of systematic error in separation below the diffraction limit and after removing these from consideration, we obtain a linear measurement uncertainty of 3-4 mas. However, if observations are unpaired or if two observations taken in the same filter are paired, it becomes harder to identify cases of systematic error, presumably because the largest source of this error is residual atmospheric dispersion, which is color dependent. When observations are unpaired, we find that it is unwise to report separations below approximately 20 mas, as these are most susceptible to this effect. Using the final results obtained, we are able to update two older orbits in the literature and present preliminary orbits for three systems that were discovered by Hipparcos
Membership of the Rosette Nebula Cluster, NGC 2244
Relative proper motions for 287 stars in the region of the young open cluster NGC 2244, located in the Rsette Nebula, have been determined from plates taken with the Yerkes 40-in. and the Allegheny 30-in. refractors. Probabilities of membership based on these proper motions are derived. Because probable members are chosen primarily from kinematic considerations, the sample should show a minimum photometric bias. Differential extinction across the cluster, however, is identified as a complication in the immediate interpretation of the sample in terms of color-magnitude diagrams or luminosity functions
Observations of Binary Stars with the Differential Speckle Survey Instrument. II. Hipparcos Stars Observed in 2010 January and June
The results of 497 speckle observations of Hipparcos stars and selected other targets are presented. Of these, 367 were resolved into components and 130 were unresolved. The data were obtained using the Differential Speckle Survey Instrument at the WIYN 3.5 m Telescope. (The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatories.) Since the first paper in this series, the instrument has been upgraded so that it now uses two electron-multiplying CCD cameras. The measurement precision obtained when comparing to ephemeris positions of binaries with very well known orbits is approximately 1-2 mas in separation and better than 0°.6 in position angle. Differential photometry is found to be in very good agreement with Hipparcos measures in cases where the comparison is most relevant. We derive preliminary orbits for two systems
Space Velocities of Southern Globular Clusters. IV. First Results for Inner-Galaxy Clusters
We have measured the absolute proper motions of four low-latitude,
inner-Galaxy globular clusters. These clusters are: NGC 6266 (M62), NGC 6304,
NGC 6316 and NGC 6723. The proper motions are on the Hipparcos system, as no
background extragalactic objects are found in these high-extinction regions.
The proper-motion uncertainties range between 0.3 and 0.6 mas/yr.
We discuss the kinematics of these clusters and of three additional bulge
clusters -- NGC 6522, NGC 6528 and NFC 6553 -- whose proper motions with
respect to bulge stars had been determined previously. We find that all of the
clusters have velocities that confine them to the bulge region. Of the three
metal poor clusters ([Fe/H] < -1.0), NGC 6522, and NGC 6723 have kinematics
consistent with halo membership. The third cluster, NGC 6266 however, appears
to belong to a rotationally-supported system. Of the four metal rich clusters
([Fe/H] >= -1.0), NGC 6304 and NGC 6553 also have kinematics consistent with
membership to a rotationally-supported system. NGC 6528 has kinematics,
metallicity and mass that argue in favor of a genuine Milky-Way bar cluster.
NGC 6316's kinematics indicate membership to a hotter system than the bar.Comment: 4 figures, 5 tables; accepted for publication in A
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
A large local rotational speed for the Galaxy found from proper-motions: Implications for the mass of the Milky-Way
Predictions from a Galactic Structure and Kinematic model are compared to the
absolute proper-motions of about 30,000 randomly selected stars with derived from the Southern Proper-Motion Program (SPM) toward
the South Galactic Pole. The absolute nature of the SPM proper-motions allow us
to measure not only the relative motion of the Sun with respect to the local
disk, but also, and most importantly, the overall state of rotation of the
local disk with respect to galaxies. The SPM data are best fit by models having
a solar peculiar motion of +5 km~s in the V-component (pointing in the
direction of Galactic rotation), a large LSR speed of 270 km~s, and a
disk velocity ellipsoid that points towards the Galactic center. We stress,
however, that these results rest crucially on the assumptions of both
axisymmetry and equilibrium dynamics.
The absolute proper-motions in the U-component indicate a solar peculiar
motion of km~s, with no need for a local expansion or
contraction term.
The implications of the large LSR speed are discussed in terms of
gravitational mass of the Galaxy inferred from the most recent and accurate
determination for the proper-motion of the LMC. We find that our derived value
for the LSR is consistent both with the mass of the Galaxy inferred from the
motion of the Clouds ( to kpc), as well
as the timing argument, based on the binary motion of M31 and the Milky Way,
and Leo I and the Milky Way ( to
kpc).Comment: 7 pages (AAS Latex macro v4.0), 2 B&W postscript figures, accepted
for publication on ApJ, Letters sectio
In-Situ Star Formation in the Outskirts of the Large Magellanic Cloud: Gaia DR2 Confirmation
We explore the Gaia DR2 proper motions of six young, main-sequence stars,
members of the Large Magellanic Cloud (LMC) reported by Moni Bidin et al.
(2017). These stars are located in the outskirts of the disk, between 7 and 13
degrees from the LMC's center where there is very low H I content. Gaia DR2
proper motions confirm that four stars formed locally, in situ, while two are
consistent with being expelled via dynamical interactions from inner, more
gas-rich regions of the LMC. This finding establishes that recent star
formation occurred in the periphery of the LMC, where thus far only old
populations are known.Comment: Accepted for publication in Astrophysical Journal Letter
Speckle observations of binary stars with the WIYN Telescope. II. Relative astrometry measures during 1998-2000
Five hundred twelve relative astrometry measures are presented for 253 double stars, including 53 double stars discovered by Hipparcos. In 15 cases, relative astrometry is reported for the first time for newly confirmed pairs. In addition, 20 high-quality nondetections of companions are reported for stars suspected of being nonsingle by Hipparcos. Observations were taken using a fast-readout CCD camera system at the WIYN 3.5 m telescope at Kitt Peak, Arizona. In comparing these measures with ephemeris predictions for binary stars with very well known orbits, we find that the measurement precision is better than 3 mas in separation and 1° in position angle per individual observation. Measurement precision and detection capabilities are fully discussed, and confirmed orbital motion is reported in four cases of the Hipparcos double star discoverie
- …