Interests and Activities

Exploring RR Lyrae Variable Stars in the Vera C. Rubin Observatory Data Preview 1

Authors: Chow-Choong Ngeow, Anupam Bhardwaj We investigate the properties of known RR Lyrae in the Vera C. Rubin Observatory Data Preview 1 (DP1) fields and compare those with the predictions based on stellar pulsation models tailored to the Legacy Survey of Space and Time (LSST) filters. The cross-match of the DP1 data with two public variable star catalogs resulted in RR Lyrae with adequate light curve sampling in five (out of seven) DP1 fields. The majority of RR Lyrae are in the 47 Tucanae and Fornax fields. We estimated photometric metallicities for these RR Lyrae using the theoretical metallicity-color relation based on -band data, and find a good agreement with literature values where the light curve sampling is sufficient for fitting template light curves accurately. The distance modulus to all RR Lyrae in DP1 fields were determined using the theoretical period-luminosity-metallicity (PLZ) relations and the period-Wesenheit-metallicity (PWZ) relation which has the smallest metallicity term. The distances based on PWZ relations are in good agreement with the literature values with a mean offset of ~mag. However, the PLZ-based distance moduli are systematically large which could be due to the theoretical calibration uncertainties that include evolved horizontal branch models. The predicted period-amplitude relations based on evolved models are also inconsistent with the amplitudes based on DP1 light curves. We conclude that the metallicity and distance estimates are sensitive to the template fitting to sparsely sampled light curves in DP1 data and future data release will significantly improve these determinations for RR Lyrae stars.

How should we look for extragalactic globular clusters with Rubin/LSST?

The amount of high-quality data made available from large sky surveys is ever-increasing. LSST is no exception. Naturally, looking for compact objects such as extragalactic globular clusters (GCs) can become extremely difficult. Even with multi-band optical photometry, GCs in distant galaxies are easily confusable with background galaxies and foreground stars. Considering the expected data from Rubin, exactly how well could we distinguish unresolved GCs from contaminants? Besides that, once we understand the limitations inherent to the data, what is the best strategy to look for extragalactic star clusters with Rubin? The SMWLV star clusters group has teamed up to answer these questions. Schweder-Souza et al. 2026 (to be published) study the expected contamination and completeness rates in samples of extragalactic GC candidates using LSST-like data of the Fornax Cluster. The colors provided by the Rubin filterset may allow us to achieve contamination rates as low as ~ 40%. However, and perhaps most importantly, sophisticated machine learning methods cannot lower this rate. Therefore, regarding the identification of extragalactic GCs, we highlight the importance of augmenting Rubin/LSST data with ancillary information. Most importantly, NIR data from surveys such as VISTA (already to be cross-matched with LSST as part of the UK in-kind contribution) and new space facilities, e.g., Roman and Euclid. With even richer datasets in terms of spectral coverage, astronomers will be able to accurately map extragalactic GC systems across immense areas of the sky, reaching high completeness rates for unprecedentedly distant galaxies and vast areas of the sky. This way, it will be possible to fully explore the scientific potential of Rubin/LSST data for extragalactic star clusters studies.

SMWLV @ LSST@LATAM 2025

Including talks by Ana Chies Santos, Yasna Órdenes-Briceño, Bolivia Cuevas Otahola, Rafael S. de Souza, Kristen Dage, & Haifeng Wang See the conference program for more.

First results on nearby low surface brightness galaxies from Rubin imaging:

The first data taken by Rubin are already starting to yield exciting science results on nearby galaxies. DP1 imaging was used to characterize the stellar populations and globular clusters of an ultra-diffuse galaxy in Romanowsky et al. (2025a). Virgo First Look provided spectacular imaging of a long stellar stream around the spiral galaxy M61 (Romanowsky et al. 2025b). for more.

nProFit

nProFit es una herramienta computacional para caracterizar poblaciones de cúmulos estelares (Cuevas Otahola et al. 2022,Cuevas Otahola in prep.) para más detalles. Actualmente nProFit se encuentra en el desarrollo de su versión 2.0, orientada para caracterizar poblaciones de cúmulos estelares en datos del LSST. Esta herramienta fue mostrada durante un tutorial y en una contribución oral durante la Reunión Latinoamericana de LSST, que se llevó a cabo en Diciembre de 2025. En este proyecto se encuentran involucrados muchos miembros de nuestra colaboración científica SMWLV.

SMWLV @ LSST@Europe6

Talks: Introduction to SMWLV, Giada Pastorelli; Early Galactic Science with LSST, Aarya Patil; Metal-poor very low-mass stars and brown dwarfs in Rubin LSST and Euclid, Nicola Lodieu; Modeling long-period variability in evolved stars for Rubin-LSST, Michele Trabucchi; Light curve’s recovery with Rubin-LSST: II. Unveiling the darkness of the galactic bulge with RR Lyrae, Marcella Di Criscienzo; Accelerating Stellar Photometric Distance Estimates with Neural Networks, Karlo Mrakovčić; PhotoD with the LSST, Lovro Palaversa See the conference program for more.

Rubin and Roman teams are committed to maximizing scientific impact through coordinated survey strategies.

Joint Rubin/Roman teams have submitted white papers to Roman's call for community input detailing how both facilities can combine data and refine survey strategies to maximize their science return. Three white papers particularly focus on Milky Way bulge and plane surveys. See Street et al., Kruszyńska et al, Abrams et al for more.

Dedicated discussion on crowded fields in microlensing session at RCW 2024

See the workshop agenda for more.

Dedicated session for Stellar Science and Crowded Fields at the RCW 2024

Discussion includes: Beyond the centroid: the need for a more complete model of LSST astrometric uncertainties (Tom J. Wilson), Synthetic LSST magnitudes derived from Gaia XP spectra (Oleksandra Razim),Ultracool Dwarfs with Rubin and Roman (Aaron Meisner), Simulating Solar Neighborhood Brown Dwarfs: A Guide for Upcoming Surveys (Easton Honaker), Mining exoplanets and benchmark brown dwarfs from large sky surveys (ZJ Zhang)

Dedicated session for SMWLV at First LSST Latin American Meeting

Discussion includes: Globular cluster systems as probes of the build-up of galaxies and their environments in the LSST era by Ana Leonor Chies-Santos (Senior Faculty, UFRGS), Characterising stellar haloes of dwarf galaxies by Elissa Tau (PhD Student, La Serena), Kinematics of the NGC 4945 diffuse stellar halo with MUSE by Camila Beltran (PhD Student, La Serena), Neighbourhood Watch: A Survey of Baryonic Substructures in the Nearby Universe by Rohan Rahatgaonkar (PhD Student, PUC)

Workshop on Ultracool Dwarfs in the Solar Neighborhood with Rubin LSST: January 2024

The Vera C. Rubin Observatory Legacy Survey of Space and Time has unparalleled capabilities to study nearby ultracool dwarfs, very-low-mass stars, and brown dwarfs. This workshop is meant to revitalize the Solar Neighbor Working Group as we approach First Light for the Observatory.

Extragalactic Globular Cluster Classification

The star clusters science working group is working on a photometric star cluster classification tool. See the Star Clusters SWG page for more.

SCOC 4th workshop

The SCOC met on January 19, 2024 to discuss plans from the strategy task forces. See more at this link.