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