204 research outputs found
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 <B < 18. The 1993 NPM1 Catalog contains
148,940 stars in 899 fields outside the Milky Way's zone of avoidance. The 2003
NPM2 Catalog contains 232,062 stars in the remaining 347 NPM fields near the
plane of the Milky Way. This paper describes the NPM2 star selection, plate
measurements, astrometric and photometric data reductions, and catalog
compilation. The NPM2 Catalog contains 120,000 faint (B > 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
(http://www.ucolick.org/~npm). 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.Comment: 44 pages, 6 figures, accepted for publication in September 2004
Astronomical Journa
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
Discovery of seven T Tauri stars and a brown dwarf candidate in the nearby TW Hydrae Association
We report the discovery of five T Tauri star systems, two of which are
resolved binaries, in the vicinity of the nearest known region of recent star
formation, the TW Hydrae Association. The newly discovered systems display the
same signatures of youth (namely high X-ray flux, large Li abundance and strong
chromospheric activity) and the same proper motion as the original five
members. These similarities firmly establish the group as a bona fide T Tauri
association, unique in its proximity to Earth and its complete isolation from
any known molecular clouds.
At an age of ~10 Myr and a distance of ~50 pc, the association members are
excellent candidates for future studies of circumstellar disk dissipation and
the formation of brown dwarfs and planets. Indeed, as an example, our speckle
imaging revealed a faint, very likely companion 2" north of CoD-33 7795 (TWA
5). Its color and brightness suggest a spectral type ~M8.5 which, at an age of
~10^7 years, implies a mass ~20 M(Jupiter).Comment: 6 pages, 4 figures and 1 table. AAS LaTeX aas2pp4.sty. To be
published in Ap
Ground-based astrometry with wide field imagers. V. Application to near-infrared detectors: HAWK-I@VLT/ESO
High-precision astrometry requires accurate point-spread function modeling
and accurate geometric-distortion corrections. This paper demonstrates that it
is possible to achieve both requirements with data collected at the high acuity
wide-field K-band imager (HAWK-I), a wide-field imager installed at the Nasmyth
focus of UT4/VLT ESO 8m telescope. Our final astrometric precision reaches ~3
mas per coordinate for a well-exposed star in a single image with a systematic
error less than 0.1 mas. We constructed calibrated astro-photometric catalogs
and atlases of seven fields: the Baade's Window, NGC 6656, NGC 6121, NGC 6822,
NGC 6388, NGC 104, and the James Webb Space Telescope calibration field in the
Large Magellanic Cloud. We make these catalogs and images electronically
available to the community. Furthermore, as a demonstration of the efficacy of
our approach, we combined archival material taken with the optical wide-field
imager at the MPI/ESO 2.2m with HAWK-I observations. We showed that we are able
to achieve an excellent separation between cluster members and field objects
for NGC 6656 and NGC 6121 with a time base-line of about 8 years. Using both
HST and HAWK-I data, we also study the radial distribution of the SGB
populations in NGC 6656 and conclude that the radial trend is flat within our
uncertainty. We also provide membership probabilities for most of the stars in
NGC 6656 and NGC 6121 catalogs and estimate membership for the published
variable stars in these two fields.Comment: 36 pages (included appendix), 13 tables, 35 figures (26 in low
resolution), accepted for publication in Astronomy and Astrophysics. Online
materials will be soon available on CDS. Meanwhile, online materials can be
requested directly to the first autho
A proper motion study of the globular cluster M55
We have derived the absolute proper motion (PM) of the globular cluster M55
using a large set of CCD images collected with the du Pont telescope between
1997 and 2008. We find (PM_RA*cos(DEC), PM_DEC) = (-3.31 +/- 0.10, -9.14 +/-
0.15) mas/yr relative to background galaxies. Membership status was determined
for 16 945 stars with 14<V<21 from the central part of the cluster. The PM
catalogue includes 52 variables of which 43 are probable members of M55. This
sample is dominated by pulsating blue straggler stars but also includes 5
eclipsing binaries, three of which are main sequence objects. The survey also
identified several candidate blue, yellow and red straggler stars belonging to
the cluster. We detected 15 likely members of the Sgr dSph galaxy located
behind M55. The average PM for these stars was measured to be (PM_RA*cos(DEC),
PM_DEC)=(-2.23 +/- 0.14, -1.83 +/- 0.24) mas/yr.Comment: 12 figures and 4 tables, accepted for publication in MNRAS Main
Journal; full PM catalogue (Table 3) at http://case.camk.edu.p
Trumpler 20 - an old and rich open cluster
We show that the open cluster Trumpler 20, contrary to the earlier findings, is actually an old Galactic open cluster. New CCD photometry and high-resolution spectroscopy are used to derive the main parameters of this cluster. At [Fe/H]=−0.11 for a single red giant star, the metallicity is slightly subsolar. The best fit to the colour-magnitude diagrams is achieved using a 1.3-Gyr isochrone with convective overshoot. The cluster appears to have a significant reddening at E(B−V) = 0.46 (for B0 spectral type), although for red giants this high reddening yields the colour temperature exceeding the spectroscopic Teff by about 200 K. Trumpler 20 is a very rich open cluster, containing at least 700 members brighter than MV=+4. It may extend over the field of view available in our study at 20 × 20 arcmin
Trumpler 20 - an old and rich open cluster
We show that the open cluster Trumpler 20, contrary to the earlier findings,
is actually an old Galactic open cluster. New CCD photometry and
high-resolution spectroscopy are used to derive the main parameters of this
cluster. At [Fe/H]=-0.11 for a single red giant star, the metallicity is
slightly subsolar. The best fit to the color-magnitude diagrams is achieved
using a 1.3 Gyr isochrone with convective overshoot. The cluster appears to
have a significant reddening at E(B-V)=0.46 (for B0 spectral type), although
for red giants this high reddening yields the color temperature exceeding the
spectroscopic T_eff by about 200 K. Trumpler 20 is a very rich open cluster,
containing at least 700 members brighter than M_V=+4. It may extend over the
field-of-view available in our study at 20'x20'.Comment: 7 pages, 5 figures; accepted for publication in MNRA
A New Proper Motion Determination of Leo I
We measure the absolute proper motion of Leo I using a WFPC2/HST data set
that spans up to 10 years, to date the longest time baseline utilized for this
satellite. The measurement relies on ~ 2300 Leo I stars located near the center
of light of the galaxy; the correction to absolute proper motion is based on
174 Gaia EDR3 stars and 10 galaxies. Having generated highly-precise, relative
proper motions for all Gaia EDR3 stars in our WFPC2 field of study, our
correction to the absolute EDR3 system does not rely on these Gaia stars being
Leo I members. This new determination also benefits from a recently improved
astrometric calibration of WFPC2. The resulting proper-motion value, (mu_alpha,
mu_delta) = (-0.007 +- 0.035, -0.119 +-0.026) mas/yr is in agreement with
recent, large-area, Gaia EDR3-based determinations. We discuss all the recent
measurements of Leo I's proper motion and adopt a combined, multi-study average
of (mu_alpha_3meas, mu_delta_3meas) = (-0.036 +- 0.016, -0.130 +- 0.010)
mas/yr. This value of absolute proper motion for Leo I indicates its orbital
pole is well aligned with that of the Vast Polar Structure, defined by the
majority of the brightest dwarf-spheroidal satellites of the Milky Way.Comment: accepted for publication in The Astronomical Journa
High-precision astrometry with VVV. I. An independent reduction pipeline for VIRCAM@VISTA
We present a new reduction pipeline for the VIRCAM@VISTA detector and
describe the method developed to obtain high-precision astrometry with the
VISTA Variables in the V\'ia L\'actea (VVV) data set. We derive an accurate
geometric-distortion correction using as calibration field the globular cluster
NGC 5139, and showed that we are able to reach a relative astrometric precision
of about 8 mas per coordinate per exposure for well-measured stars over a field
of view of more than 1 square degree. This geometric-distortion correction is
made available to the community. As a test bed, we chose a field centered
around the globular cluster NGC 6656 from the VVV archive and computed proper
motions for the stars within. With 45 epochs spread over four years, we show
that we are able to achieve a precision of 1.4 mas/yr and to isolate each
population observed in the field (cluster, Bulge and Disk) using proper
motions. We used proper-motion-selected field stars to measure the motion
difference between Galactic disk and bulge stars. Our proper-motion
measurements are consistent with UCAC4 and PPMXL, though our errors are much
smaller. Models have still difficulties in reproducing the observations in this
highly-reddened Galactic regions.Comment: 11 pages, 10 figures (some in low res), 1 table. Accepted for
publication in MNRAS on March 25, 2015. The FORTRAN routine will be soon made
available at http://groups.dfa.unipd.it/ESPG/ , and via email request to the
first autho
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