The Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) will revolutionize our current
astrophysical and cosmological knowledge of the Universe thanks to its long-term, sensitive, multi-band
photometry. This experiment will collect data in six different photometric (ugrizy) bands, over a time scale
of ten years. LSST’s field of view is almost ten square degrees and it will scan the entire Southern sky
approximately every three nights. The 8 metre class telescope will allow us to reach a depth of r∼24 mag
per single exposure. With these limiting magnitudes, the photometric accuracy and the homogeneity of
the data, the survey will exceed current limits set by Gaia several order of magnitudes both in depth and
in completeness.
The early LSST data releases, with the first planned in 2026, will be a goldmine to characterize resolved
stellar populations in Local Group (LG, d<1 Mpc) and unresolved stellar populations in Local Volume
(LV, d<25 Mpc) galaxies and to constrain on a quantitative basis the early formation and evolution of the
Milky Way (Galactic bulge, halo, disks) and nearby stellar systems. The six photometric bands range
from almost the limit of the atmospheric cutoff (λeff (u)∼3500 A˚ ) to the near-infrared (λeff (y)∼10000
1
A˚ ), meaning that a strong sensitivity in effective temperature presents us with the unique opportunity to
unveil stellar populations in highly reddened regions (bulge, core nearby dwarf galaxies). Moreover and
even more importantly, LSST plans to adopt an ad hoc reduction strategy, in tandem with crowded field
photometry developed by in-kind contributions, to perform accurate and deep photometry even in the
most crowded stellar fields.
For these reasons, LSST will be a game changer across a wide variety of astrophysical fields, particularly
the field of stellar astrophysics. At the end of the mission, the limiting magnitudes reached by LSST will
allow us to identify and characterize all southern stellar systems located within roughly one Mpc. This
will be the largest and most homogeneous demographic investigations of resolved stellar populations in
the Local Universe. The observing strategy and the cadence of the images in the different photometric
bands will also allow us to identify and characterize periodic and aperiodic astrophysical phenomena
ranging from tens of seconds to years.
Searching through the avalanche of data acquired by LSST will be a major challenge: it is expected that
the survey will produce on average 15 terabytes of data per night. Roughly 100 petabytes of data will be
collected at the end of the 10-year experiment. New and dedicated high performance computing facilities
will process the huge amount of raw and scientific images, almost in real time, and a re-processing of the
entire data set is planned on an annual scale. The identification and characterization of variable stars
and all kinds of stellar populations will require sophisticated techniques of Artificial Intelligence/Machine
Learning (AI/ML). We are entering a new era in which a sophisticated data management system, the
Rubin Science Platform, will enable database queries from individual astronomers to use the entire
data set collected by LSST. In addition to the data releases, Rubin Observatory will produce a public
stream of alerts containing nightly data about transient, variable and moving sources. LSST alert brokers
will receive these alert streams and redistribute them, bringing LSST data closer to science users,
as well as promoting citizen science projects. According to the Rubin Observatory construction
plans (https://www.lsst.org/about/project-status), the very first images collected with the LSST
Camera will become available to the data-holders at the beginning of the next year. Soon after,
the second data preview (DP2) is planned, while the first data release (DR1) is currently scheduled
for the end of 2026 / early beginning of 2027. While some schedule delays on the order of
months may still be possible with this ambitious a project, Rubin’s Data Preview 1 has already been
released, with new science results forthcoming. Therefore, by mid 2027, we expect any delays would
not significantly limit the outcomes of this meeting, and indeed shows that June/July 2027 is the perfect
time to bring the international community together to prepare for next-generation science with the Vera
Rubin Observatory.
For these reasons, we propose to hold the VEra Rubin ObservatorY: Stars and Stellar Systems (VERYTAS)
program. VERYTAS will allow us to bring together researchers from four different astrophysical
communities, who work on similar astrophysical problems, but with different observables and different
approaches: a) – Stellar astrophysicists dealing with periodic and aperiodic variable stars. Optical variability
ranging from compact objects (white dwarfs, neutron stars, stellar mass black holes), to hydrogen
and helium burning variable stars, to the zoo of geometrical variables. b) – Astrophysicists interested
in using chemistry (elemental abundances), photometry (colors, distances, reddening) and kinematics
(radial velocity, proper motion, orbital parameters) to constrain the assembly history of nearby stellar
systems. c) – Cosmologists dealing with numerical simulations including dark matter, star and gas components
of Milky Way-like galaxies and stellar systems (open, globular clusters). d) – Astrophysicists
interested in developing new algorithms and new AI/ML methodologies to efficiently and accurately mine
the wealth of information that LSST will provide to the astronomical community.
The diversity of scientific objectives, combined with the novelty of the methodological approach make
VERYTAS unique, with far-reaching implications for our understanding of stellar physics and stellar dynamics,
and transformative insights into data intensive techniques.