HST: van Altena has been involved with
the Hubble Space Telescope from the
beginning of Phase B in 1972, first as Team Leader of the HST Investigation
Definition Team for Astrometry, and from 1977 through 1999 as a Team Member
of the HST Astrometry Science Team. His HST research has been primarily
directed towards the determination of parallaxes of the Hyades Cluster
and various astrophysically interesting stars, as well as determination
of the internal motions of several Globular Clusters based on first and
second exposures (1992 to 2000) that we have taken with the WFPC and WFPC2
cameras on HST. The latter project has research goals of studying the variation
and isotropy of the clusters' internal kinematics as a fuction of distance
from the cluster center and mass, as well as determining kinematic distances
to the clusters based on a comparison of our measured proper motion dispersions
with the existing radial velocity dispersions. Collaborating individuals
include: T. Girard, J. T. Lee, C. Bailyn, G. Drukier, D. Dinescu, J. Nuñez
and W. van Altena.
FAME: The Full-Sky
Astrometric Explorer is a scanning astrometric satellite similar to
Hipparcos in concept but with capabilities extended to observe 50 million
stars to a position and parallax precision of 50 µas, and a proper
motion precision of 50 µas/yr to the 9th magnitude and reduced precision
to the 15th magnitude. van Altena is a member of the FAME Science Working
Group with research interests in determining the distances to, and the
membership in, about 100 Open Clusters to the 15th magnitude, establishing
a Pop II distance scale based on parallax determinations of Subdwarf stars,
refining the stellar Mass-Luminosity relation, and studying the local stellar
and kinematic structure of our Galaxy.
SIM: The Space
Interferometer Mission is a pointed Michelson Interferometer satellite
with a 10-meter baseline designed to determine stellar positions and parallaxes
with an accuracy of 4 µas, and a proper motion accuracy of 4 µas/yr
to the 20th magnitude for a few thousand stars. van Altena was a member
of the Science Working Group of SIM and he has proposed for a Key Project
for the determination of the Pop I Cosmological Distance Scale based on
the determination of absolute parallaxes of Cepheid variables, Open Clusters,
and young OB stars. Collaborating individuals include: T. Girard, I. Platais,
B. Madore, P. Demarque, R. Olling, E. Horch, L. Berdnikov, R. Méndez,
and W. van Altena.
Return
to Research Page
Astrometry
Techniques
Absolute Proper Motions:
The
Southern Proper Motion program (SPM) is a collaborative project between
the Yale Southern Observatory
(YSO) and the Universidad Nacional de San Juan, Argentina. Absolute
proper motions are being determined for stars in the magnitude range 5
< V < 19 for millions of stars with declinations < -17 degrees.
The research goals of the SPM are to study the kinematic structure of our
Galaxy and to establish a Faint Reference System in the Southern Hemisphere.
Up to date progress on the SPM is available on the SPM Web page. Collaborating
individuals include: T. Girard, I. Platais, V. Kozhurina-Platais, C. E.
López, D. Dinescu, R. Méndez, and W. van Altena.
Relative Proper Motions: Numerous papers
have been published providing membership and internal motions in Open Clusters
based on high precision relative proper motions. Current research is primarily
in association with the WOCS research group and their efforts to determine
membership in selected Open Clusters to very faint magnitudes, as well
as with the determination of the internal kinematics and distances of Globular
Clusters based on Hubble Space Telescope observations. Collaborating individuals
include: T. Girard, I. Platais, V. Kozhurina-Platais, D. Dinescu, R. Méndez,
and W. van Altena.
Stellar Parallaxes: Numerous papers
have been published on the determination of stellar parallaxes, both from
the ground and from space, the most recent being the determination of the
parallax of the Hyades Cluster based on parallaxes determined with the
Fine Guidance Sensors of the Hubble Space Telescope. In 1995 we published
the Fourth Edition of the General Catalog of Trigonometric
Stellar Parallaxes, which is a compilation and critical evaluation
of all parallaxes published from 1900 to 1995. Spectrophotometric parallaxes
are also being determined for the reference stars in HST parallax fields
based on spectra taken with the MOS/Hydra spectrgraph on the WIYN 3.5-meter
telescope. Collaborating individuals include: D. Hoffleit, J. Lee, and
W. van Altena.
Return to Research Page
Objects of
Interest
Galactic Structure: The local structure
of our Galaxy can be studied through the use of absolute proper motions
and distance estimators such as the star's magnitudes and colors. We have
used the first results of the SPM observations in the vicinity of the South
Galactic Pole, i.e. the SPM
1.1 Catalog, to study the Solar Motion, and streaming motions of the
stars as a function of distance below the galactic plane due to galactic
rotation. More extensive investigations will be undertaken as we complete
additional zones of the SPM. Collaborating individuals include: T. Girard,
I. Platais, V. Kozhurina-Platais, C. E. López, D. Dinescu, R. Méndez,
and W. van Altena.
Open Star Clusters: The Yale Astrometry
Group has been active for many years in the determination of the membership
and internal motions in Open Clusters based on high-precision proper motions.
Use of the refined membership lists has enabled Yale researchers and the
WOCS collaboration members to fit stellar evolution isochrones to the color-magnitude
diagrams and derive improved ages and stellar internal structure parameters.
Recently studied Open Clusters include NGC 2451, Blanco 2, M35 and NGC
188. Collaborating individuals include: T. Girard, I. Platais, V. Kozhurina-Platais,
D. Dinescu, P. Demarque, and W. van Altena.
Globular Star Clusters: One of our
two major research projects, as a part of our participation in the HST
Astrometry Science Team, has been the determination of very precise relative
proper motions in Globular Clusters. These proper motions will be used
to measure the internal velocity dispersions as functions of distance from
the cluster center and stellar mass, and to study the degree of anisotropy
and, in comparison with independently determined radial velocities, the
kinematic distances to the clusters. The clusters being studied include:47
Tuc, NGC 6752, M3, M13, M15, and M22. In a separate ground-based project,
we are determining the tangential velocities and galacto-centric orbits
of Southern Hemisphere Globular Clusters, as well as the Magellanic Clouds,
based primarily on plates taken for the SPM project. Collaborating individuals
include: T. Girard, C. Bailyn, G. Drukier, D. Dinescu, and W. van Altena.
Near Earth Objects: We have an active
program for the observation of NEO's and Minor Planets from the Cesco Observatory
at El Leoncito, Argentina which the Yale Southern Observatory, Inc. runs
in collaboration with the Universidad Nacional de San Juan, Argentina.
Our newly installed CCD system on the Double Astrograph is capable of reaching
NEO's to the 20th magnitude and is used primarily to observe those objects
that are moving south and in danger of being lost due to their poorly known
orbits. Collaborating individuals include: C. E. López, T. Girard,
D. Rabinowitz, R. Branham, R. Meyer and W. van Altena.
Binary Stars: The observation of binary
stars using high-resolution techniques such as
Speckle Interferometry and
the HST Fine Guidance Sensors has been an important part of Yale Astrometric
research for many years. HST observations of binary stars has been primarily
undertaken under the leadership of O. Franz of the Lowell Observatory,
while ground-based Speckle Interferometry of binary stars has been under
the leadership of E. Horch, now of the Rochester Institute of Technology
Center for Imaging Sciences. Speckle observations are currently being made
with the WIYN 3.5-meter telescope of stars proposed as members of the SIM
grid, stars suspected of being binaries from Hipparcos observations, and
binaries in need of improved orbits. Observations are also being made to
develop improved methods for the determination of magnitude differences
in binary stars and a new highly efficient Speckle Interferometer is also
being developed. Collaborating individuals include: C. E. López,
T. Girard, E. P. Horch, R. Meyer and W. van Altena.
Faint Reference System: As a part of
the SPM, we are establishing
a relatively high density extension of the Hipparcos/ICRS bright star (V
< 10) reference system to the 18th magnitude. Work has already been
completed on major parts of the -20 to -40 degree zones based on the already
published SPM catalogs. Further information is available on the extension
on the SPM Web page. Collaborating individuals include: T. Girard, I. Platais,
V. Kozhurina-Platais, C. E. López, and W. van Altena.
Return
to Research Page