Letters of Intent received in 2022

LoI 2024-2184
Towards Multi-wavelength Astrometry

Date: 14 August 2024 to 15 August 2024
Category: Focus meetings (GA)
Location: Cape Town, South Africa
Contact: Christopher Jacobs (Chris.Jacobs@jpl.nasa.gov)
Coordinating division: Division A Fundamental Astronomy
Other divisions: Division B Facilities, Technologies and Data Science
Chair of SOC: Christopher Jacobs (JPL, Caltech)
Chair of LOC: Glenda Coetzer (SARAO)



Review talk on the state of Modern Astrometry at Multiple Wavelengths

Science Highlights at multiple wavelengths:
- Gaia DR3 and progress towards DR4
- Progress towards a next generation multi-wavelength ICRF
- AO assisted narrow field differential optical astrometry e.g. galactic center studies
- sub-mm VLBI e.g. EHT at 780 microns (345 GHz)
- optical interferometers e.g. the VLT’s GRAVITY program at 2 microns

Spacecraft tracking and navigation based on astrometric measurements
- Radio measurements (VLBI, Doppler and Range) for interplanetary navigation
- Optical measurements of spacecraft trajectories

Differential VLBI astrometry of AGNs, masers, and other natural sources.
-Mapping the galaxy with VLBI astrometry of water masers
- prospects for improved accuracy

Astrometry from extremely large telescopes
- large sky surveys
- the need for very dense reference frames

Astrometric technique development including opportunities for cross-fertilization amongst wavelengths
- Managing Big Data: approaching the Petabyte regime
- Lessons from Gaia analysis
- Differential ground based optical interferometry e.g. GRAVITY
- Ground based optical/IR surveys e.g. PanSTARRS, LSST
- SKA astrometric capability development
- VLBI astrometry above 100 GHz

- astrometric and complementary databases e.g. photometric, and spectroscopic surveys
- wavelength synergies: optical-IR-radio
- space-ground synergies

Future ground and space-based astrometric surveys.



The field of astrometry has made tremendous progress over the past several years
in the number of objects measured, the accuracies achieved, and the range of wavelengths covered.
Large projects such as Gaia now measure billions of objects.
Differential measurements at both the radio and optical/IR wavelengths
now achieve accuracies on the order to 10 µas!
Wavelengths now range from several centimeters down to 2 microns:
- GaiaNIR is the proposed successor Gaia's optical mission.
-The next generation ICRF is slated to cover multiple radio as well as Gaia optical wavelengths.
-The Koreans are developing a simultaneous 4-band VLBI system going to 129 GHz (1.8mm)
- The EHT team is looking to extend VLBI into the sub-mm regime (345 GHz, 870 microns)
- The VLT's GRAVITY project is producing interferometry in the 2 micron band.

The Gaia catalog has enabled advances in diverse fields ranging from exo-planets to
white dwarfs, to proto-planetary disks, to refinement of the Hubble-Lemaitre constant
which in turns aids dark energy studies. Closer to home, hundreds of thousands of
Solar system objects such as asteroids are now being tracked by Gaia.

On the ground, optical/IR interferometry is realizing it’s long appreciated potential
with instruments such as the VLT’s GRAVITY instrument producing ~10 µas
accuracies over narrow fields.

In the radio, differential VLBI is producing similar ~10 µas accuracies
with exciting applications such as mapping the structure of our galaxy.
The VLBI technique is pushing to higher frequencies and thus higher resolution.
For example, the Korean VLBI network is producing results with as many as
four simultaneous bands and frequencies as high as 129 GHz. The Event Horizon Telescope
has pushed the VLBI technique up to 230 GHz with plans to go even higher
to realize many-fold increases in resolution.

Global scale Celestial Reference Frame (CRF) work at both optical and radio wavelengths continues to
progress with precision often better than 100 µas. Alignment amongst CRFs
at various wavelengths is on the order of a few 10s of µas with potential for zonal errors to
be reduced to similar levels. The time is now to work towards an IAU standard multi-wavelength
frame to enable registration across wavelengths at the the highest accuracies.

Our proposed focus meeting aims to bring together the practitioners and users of
high accuracy astrometric data in order to
inform the community on recent scientific successes in astrometry.
to educate the community on advances in astrometric techniques across
different wavelength ranges and instrument concepts.
and to inspire future advances.

In particular, we aim at bringing together the various astrometry communities
(Optical/IR, radio, ground and space-based surveys, specialized astrometric instruments) which
often work in relative isolation from each other. Our proposed meeting would promote
understanding of the complementarity of the various branches of astrometry and thus
reveal synergies between the different astrometric techniques
thereby driving the definition of future directions for our discipline.

In order to strengthen the astrometric community, the scientific organizing
committee of this focus meeting will have representatives from the
various branches of astrometry mentioned above (optical/IR, radio, ground and space-based)
as well as gender balance and broad geographical representation.