The Gaia NIR mission and the engagement of the Spanish Community

28 Jan 2026, 09:00 → 30 Jan 2026, 14:00 Europe/Madrid

Agencia Espacial Española (AEE) headquarters in Sevilla

The proposal of a new astrometric space mission, GaiaNIR, was submitted to ESA in response to the call for Voyage 2050 and was recommended by the Senior Committee. Built on the Gaia principles, GaiaNIR is an astrometric mission in the near IR, candidate for the ESA Voyage 2050 L5 launch slot. The main goals are to explore the previously inaccessible components of the Galaxy, obscured by dust, in the near-IR and to achieve a significant improvement in parallaxes and, most importantly, in proper motions by combining Gaia's epochs with new observations over a 20-year period.  Improved astrometry allows to enlarge the original Gaia science cases, from the details of the dusty spiral arms to exoplanets in dusty and star forming regions to IMBH embedded in clusters or wide binaries. We plan to identify which science cases can benefit from a GaiaNIR-like mission. Finally, this will ensure a revision of the Gaia reference frame. 

 The Spanish industry and scientific community, fully involved in the Gaia mission, join in this meeting to discuss the technical and scientific challenges of GaiaNIR. The most updated design and status of the GaiaNIR mission will be addressed by the international core team.    

 In this meeting we plan to cover the following topics:

• Mission overview: we count with the presence of Dr. David Hobbs (Lund observatory) to give a review talk.

• Technical challenges of the mission

• IR Astrometry scientific challenges & big science questions

• Round table with the Spanish industry

• Requests on simulations

• Synergies with other missions

• Round table on the actions for future Spanish enrollments

 

There is a small number of slots allocated for short talks. Please, submit your abstract using the Call for Abstracts before December 1st 2025.

 The meeting will be hybrid.

Scientific Organizing Committee (SOC):

• Giuseppina Battaglia (IAC)
• Jose Caballero (CAB)
• Josep Manel Carrasco (UB)
• Minia Manteiga (UdC)
• Mercè Romero-Gómez (UB, Chair)
• Rainer Schödel (IAA)

Registrations GaiaNIR Sevilla 22012026

Right of information in relation to the data processing Gaia NIR.pdf

Wednesday 28 January

09:00 → 10:59 REG: Herramientas para Gaia DR3 y DR4 (I)

09:00 Bienvenida

09:30 Gaia DR4: What can we expect from the coming data release

Gaia DR4 is planned for December 2026, covering the five years of nominal Gaia mission, and will include 'everything'. It will consist of more than 140 tables and of the order 500 TB of data. We give a brief overview of the various data products and how they are organized. With respect to Gaia DR3, the uncertainties will improve significantly and the release now includes the epoch data for astrometry, photometry and spectroscopy, allowing a much more flexible use of the data. Gaia DR5, for the full ten years of mission, will give another leap in precision but is not expected before the end of 2030.

Speaker: Claus Fabricius (IEEC-ICCUB)

09:50 Computing magnitudes, colours, distances at any signal-to-noise level

While it is in general preferable to work with parallaxes instead of distances, some applications may make a conversion from parallaxes to distances desirable. At low signal-to-noise levels random noise may however cause the observed parallax to become negative. The conversion from parallax to distance has therefore to take the non-negativity of the true parallax, and distance, properly into account. This can be done by using a suitable prior. We present a rigorous prior that results in a simple "all-purpose" estimator for the distance from the parallax and its error at all signal-to-noise levels. This estimator is easy to compute with low computational effort, and thus suitable for applications to large data set. We show that the estimator provides distances that are less biased than distances computed using previous priors, and also less prone to produce "outliers" in the distances. The same approach can also be applied in the computation of magnitudes and colours from observed fluxes at low signal-to-noise levels.

Speaker: Michael Weiler (IEEC-ICCUB)

10:10 The Galactic bar revisited. What could we expect from Gaia NIR?

Brief presentation on some new results of the long bar morphology using several stellar catalogues. An short extrapolation of what could be expected using NIR astrometric data will be given.

Speaker: Francisco Garzón (IAC)

10:17 Milky Way spiral arms across stellar populations

The Milky Way’s (MW) spiral structure has been longly studied using several tracers; however, it is not unambiguously determined yet. We address this by combining a hydrodynamical simulation and observational data.
In our simulation, stellar populations as old as 11Gyr and with velocity dispersions up to ~90km/s have overdensities coincident with the youngest spiral arms at all times. The global spiral pattern is transient on timescales of roughly 100Myr and shows disconnections and reconnections of arms segments. Young stars react faster to this evolution than old stars, which produces stronger arms in the first case. However, the scaling between arm strength and stellar age evolves with time depending on the strength of the global spiral structure.
In the case of the MW, we use a sample of A-type stars to demonstrate that this intermediate-age population also shows spiral substructure. Furthermore, our sample also reveals the kinematic signature of the Galactic warp.
Studying the interplay between all stellar populations is key to understanding the nature of MW’s spiral structure.

Speaker: Judith Ardèvol (Universitat de Barcelona (ICCUB - IEEC))

10:24 Vertical kinematics and structure of the Local Arm: from young clusters to GaiaNIR

Within the Local Arm Structure project we investigate the three-dimensional distribution and vertical kinematics of young tracers in the Orion (Local) arm using Gaia astrometry and recent catalogues of open clusters and star-forming regions. Building on our results in Vertical kinematics of the young Galactic clusters (Alfaro, Sánchez-Gil & Elmegreen 2025, MNRAS, doi:10.1093/mnras/staf155), we show that clusters younger than ≲30 Myr define an almost linear relation in the V_Z plane, consistent with a vertical harmonic oscillator and providing independent constraints on the effective local mass density.

In this flash talk I will present our ongoing work on the spatial structure of the Local Arm and its surroundings, aiming to characterise the nature of arm segments and filamentary groupings, including candidates for inter-arm structures. Using the 3D positions (X,Y,Z) of young clusters and associations, we apply minimum spanning tree (MST) analysis and Gaussian Mixture Model (GMM) classification to identify coherent structures and quantify their geometry, connectivity, and contrast with respect to the underlying disc. I will also outline how adding near-infrared astrometry from a GaiaNIR-like mission would allow us to extend this analysis into highly extincted regions, tracing these filaments and arm segments where Gaia alone becomes incomplete and testing whether their properties change between optically visible and dust-obscured parts of the spiral pattern.

Speaker: M Carmen Sánchez Gil (Universidad de Cádiz)

10:31 Chronology of our Galaxy from Gaia color-magnitude diagram fitting (ChronoGal)

I will present a brief overview of the ChronoGal project which has recently been awarded an ERC advanced grant.

Speaker: Carme Gallart (IAC)

10:38 Inference of the Galactic SFH and IMF from BGM FASt and Gaia DR3/DR4

Despite the fundamental role of the star formation history (SFH) and the initial mass function (IMF) in describing the Milky Way—and their intrinsic correlation—their consistent and robust determination remains challenging. The unprecedented astrometric and photometric precision of Gaia provides a unique opportunity to address this long-standing problem. I will present a new implementation of the Besançon Galaxy Model Fast Approximate Simulations (BGM FASt), a population synthesis framework designed to efficiently generate synthetic Milky Way stellar catalogs. By fitting Gaia DR3 color–magnitude diagrams, we make a robust derivation of the 2nd and 3rd slopes of the IMF and obtain an SFH in the Solar neighborhood characterised by a hiatus 6 Gyr ago, a bump with a wide plateau from 6 to 2 Gyr ago, and an accurate increase in the last Gyr (del Alcázar-Julià et al. 2025). I will compare our findings with recent studies, including Fernández-Alvar et al. (2025) and Alzate-Trujillo et al. (2025). Finally, I will discuss the ongoing work and how BGM FASt will benefit from the upcoming Gaia DR4, expected by the end of this year, whose improved parallaxes, proper motions, and radial velocities will allow for a more detailed characterization of the different Galactic components and their role in the Milky Way assembly history.

Speaker: Marc del Alcázar i Julià (ICCUB - IEEC)

10:45 N-body simulations of the Milky Way

Gaia data provide a detailed snapshot of the local structure of our Galaxy. However, to understand the global dynamical structure of the Milky Way and its time evolution, it is essential to compare observation data with theoretical models. In this context, I have been using high-resolution N-body simulations as theoretical counterparts of the Milky Way. Recent advances in GPU computing enable simulations with billions of particles. In this short talk, I will briefly introduce our previous studies on disc dynamics using both isolated and perturbed N-body simulations, demonstrating the potential of high-resolution N-body simulations.

Speaker: Tetsuro Asano (IEEC-ICCUB)

10:52 Creating realistic Gaia-like mock of dwarf galaxies

I will present a method we develloped at the IAC to create realistic Gaia-like mock of dwarf galaxies, which includes a method to optain the uncertainties from a wide set of parameters.

Speaker: Guillaume Thomas (IAC/ULL)

11:00 → 11:30 Coffee Break

11:30 → 12:56 REG: Herramientas para Gaia DR3 y DR4 (II)

11:30 SPACIOUS: A practical guide (overview, usage and proposals)

SPACIOUS (Science PlAtform Cloud Infrastructure for Outsize Usage Scenarios) is a cloud-ready science platform built to make the exploitation of large space-mission datasets more scalable, interactive, and reproducible, leveraging big-data and data-mining technologies. In this talk, I will give a practical overview of what SPACIOUS provides today and how to get started with typical “astronomer-first” use cases. I will finish with a short roadmap for turning a science case into a SPACIOUS-ready proposal.

Speaker: Alfred Castro-Ginard (Universitat de Barcelona)

11:45 Data fusion of Gaia with other catalogues: Gaia and J-PLUS (proof-of-concept)

We have combined part of the Gaia DR3 catalogue (GaiaSource and EpochPhotometry) with the photometry and classification data from J-PLUS DR3 in a single table, also including the distance estimator by M. Weiler. It is available as partitioned Parquet files, including an index which allows to download just the relevant files for each use case. Additionally, we provide an experimental online service, with Jupyter notebooks and this table ingested in a fast database. All this is a good appetizer for the format and data volume that we will see in Gaia DR4, as well as for the kind of tools that will be provided for its exploitation.

Speaker: Dr Jordi Portell de Mora (ICCUB)

12:00 Gaia and the J-Surveys: A Match Made in Heaven

Thanks to large public spectroscopic surveys, we now possess a wealth of high-quality chemical-abundance data for Milky Way stars. This has significantly advanced our understanding of the Galaxy’s evolution and mass-accretion history, but these surveys remain inherently biased by their pre-selection requirements. Gaia overcomes many of these limitations by providing unparalleled all-sky astrometry and low-resolution spectrophotometry. Yet, even with the upcoming DR4, Gaia’s BP/RP spectra struggle to deliver precise chemical information for faint, distant stars, the very populations that hold the earliest record of Galactic assembly.

Here, multifilter surveys such as J-PLUS and J-PAS offer a powerful solution. Their high-S/N, multi-band photometry captures low-resolution SEDs with far greater sensitivity than Gaia XP at faint magnitudes, supplying crucial chemical constraints. In this talk, I will present results combining Gaia DR3 with J-Surveys photometry using BANNJOS, a Bayesian neural-network pipeline that delivers stellar classifications, atmospheric parameters, and elemental abundances with full posterior PDFs. This synergy, photometric chemistry from J-Surveys combined with Gaia’s astrometry, allows us to trace both the ages and chemical composition of stars deep into the Galactic halo.

The deeper XP spectra of Gaia DR4, together with forthcoming releases of J-PLUS and J-PAS, will further enhance this complementarity, paving the way toward the most detailed 3D chemical maps of the Milky Way to date.

Speaker: Andrés del Pino Molina (Instituto de Astrofísica de Andalucía (IAA-CSIC))

12:07 A Massive Star Census of the Magellanic Cloud

The fourth phase of the Alma Luminous Star (ALS) catalogue aims to create the most comprehensive and complete sample of massive stars in the Magellanic Clouds (MCs). By combining Gaia DR3, which provides high-precision photometric and astrometric data, with SIMBAD, which compiles complementary information from the literature, such as spectroscopy classification, we can identify likely massive stars based on photometry cuts
and star identifiers. Incorporating additional datasets, including UBV photometry from Zaritsky et al. (2002, 2004) and JKs photometry from VISTA and 2MASS, allows us to filter out the remaining intermediate-mass stars effectively. Consequently, our sample encompasses not only the clearly massive stars above the 8 solar masses isochrone in the Color-Magnitude Diagram (CMD), but also reddened massive stars below it that are
often overlooked in previous catalogues. The final catalogue will cover both the Large and Small Magellanic Clouds (LMC and SMC) as well as the Magellanic Bridge (MB), providing a valuable resource for studies of the MCs’ structure, peculiar stellar populations, refinement of the Initial Mass Function (IMF), and investigations into extragalactic black holes and gravitational waves, among other applications.

Speaker: Juan Antonio Molina Calzada (CAB (CSIC-INTA))

12:14 How to brake a bar: tidal interactions can slow down the bar pattern speed

In this talk, I will present our recent results showing that tidal interactions can strongly affect the dynamical state of stellar bars, and in extreme cases can effectively halt their rotation. Using controlled interaction models motivated by the XMC system, we find that bars can experience a rapid drop in pattern speed down to nearly zero on short timescales around pericentric passages, while also undergoing substantial weakening and subsequent re-growth. This provides a physically motivated pathway to explain slowly rotating or non-rotating bars in interacting galaxies, and supports the interpretation that the LMC may host a bar in a very low-pattern-speed state. I will close by discussing why these results reinforce the need for caution when interpreting bar properties in cosmological simulations, where numerical resolution and time-dependent environments can bias both bar formation and the inferred bar evolution due to not resolving properly all type of bar stellar orbits.

Speaker: santi Roca-Fàbrega (Universidad Complutense de Madrid)

12:21 Missing RR Lyrae Binaries: Observational Biases or Model Tension?

Metal-rich RR Lyrae stars in the Milky Way disc challenge their classical interpretation as purely old tracers. Binary evolution has been proposed as a viable formation channel, predicting a significant population of long-period RR Lyrae binaries. However, none have been robustly identified so far, including in Gaia DR3.
In this talk, I show that Gaia DR3 non-detections already point to a tension with current binary-formation models, but do not yet provide a definitive test. Using a carefully selected sample of Gaia RR Lyrae stars and realistic simulations of Gaia astrometry, we find that intrinsic stellar variability strongly suppresses binary detectability, substantially weakening constraints on the binary fraction. As a result, while the data disfavour the highest binary fractions predicted by some models, firm conclusions cannot yet be drawn.
Gaia DR4, together with an explicit treatment of stellar variability, will be crucial to resolving this tension.

Speaker: Giuliano Iorio (University of Padova)

12:28 RR Lyrae: Pulsating Tracers of the Milky Way with Gaia and J-VAR/J-PLUS

RR Lyrae stars are powerful pulsating tracers of the Milky Way’s structure and stellar populations. We present a catalog of 315 RR Lyrae light curves combining Gaia DR3 with J-VAR DR1 observations from the JAST80 telescope at the Observatorio Astrofísico de Javalambre, complemented by J-PLUS multi-filter photometry. We will also present preliminary results from the analysis of Gaia–J-PLUS RR Lyrae light curves, highlighting trends in multi-band amplitudes and their potential for population studies. This work illustrates the value of combining current surveys as a pathfinder for future Gaia-based and GaiaNIR astrometric science.

Speaker: SAYALI KULKARNI (Centro de Estudios de Física del Cosmos de Aragón)

12:35 Stellar Parameters Using J-PLUS DR4 Photometry and Gaia Parallaxes via PCA

Accurately deriving stellar parameters Teff, log g, [Fe/H], and [α/M] for millions of stars is critical for unraveling the Milky Way’s formation and evolution, yet spectroscopy remains costly and prone to selection biases. We present a purely algebraic method that recovers these quantities from a combination of multifilter photometry and parallax from Gaia DR3: a principal-component analysis (PCA) of colours and distance modulus followed by low-order polynomial regression. The approach is flexible, easy to interpret, requires only a modest spectroscopic training set from LAMOST, and can be applied to any survey. Applied to J-PLUS DR4, which images around 5000 deg² with 12 bands (seven of them narrow), it yields a catalogue of fifteen million stars whose parameters reproduce independent LAMOST measurements with precision comparable to that of low-resolution spectra, where parallaxes from Gaia allow us to predict surface gravity. This photometric catalogue enables science that would be difficult with spectroscopy alone, such as systematic selection of metal-poor ([Fe/H] ≲ –1.5) populations to trace ancient merger debris and study them with Gaia astrometry, mapping of stellar streams across thousands of square degrees, or automatic flagging of white dwarfs through their distinctive location in the [α/M]–[Fe/H] and log (g) – Teff planes. Because the model is survey-agnostic and lightweight, it remains effective even when only a handful of spectra are available, making it ideal for sparsely sampled regions.

Speaker: Adrián Hidalgo Pinilla (Centro de Estudios de Física del Cosmos de Aragón)

12:42 A Gaia+VVVX census of FGKM and ultracool stars toward the GC with prospects for Gaia NIR

We present CeVeSo-GC, a project aimed at building a homogeneous census of FGKM and ultracool stars out to 500 pc in the direction of the Galactic Center — a region still poorly characterized due to crowding and extinction.
The catalog is constructed by combining Gaia DR3 optical astrometry with deep VVVX near-infrared photometry, enabling distance estimation (parallactic or photometric), temperature and spectral-type determination, and population classification. We will identify key scientific subsets including young stars, metal-poor subdwarfs, ultracool dwarfs, potential exoplanet hosts, and unresolved binaries. ML techniques will be used to evaluate contamination and completeness, and spectroscopic/high-resolution imaging follow-up is foreseen to refine parameters and multiplicity assessments.

We will discuss how Gaia NIR will dramatically extend this work by improving parallaxes and proper motions, increasing completeness for cool and faint objects, and mitigating extinction toward the bulge. This mission will enable a more complete and precise characterization of the Solar Neighborhood toward the Galactic Center, opening new avenues for Galactic structure, stellar evolution, chemical-abundance studies, and exoplanet searches around M dwarfs.

Speaker: Javier Banegas Paredes (Universidad Complutense de Madrid)

12:49 Cataclysmic Variables in Gaia DR3: spectra and light curves

Cataclysmic Variables (CVs) are interacting binaries made of a white dwarf accreting material from a low mass main sequence Roche-lobe filling secondary star. I use machine learning algorithms to both Gaia low resolution spectra and light curves to identify new objects belonging to this class. Suggestions and advice on the use of spectra is welcome.

Speaker: Alessandro Ederoclite (CEFCA)

13:00 → 15:00 Lunch break

15:00 → 16:40 Mission overview

15:00 Welcome and summary of the ministerial meeting

Speaker: Isabel Pérez Grande (Directora de Ciencia, Tecnología e Innovación AEE)

15:15 Spanish industrial partners, current developme

Speaker: Cecilia Hernández (TBC)

15:30 Voyage 2050: GaiaNIR in context

Speaker: Frédéric Safa (ESA)

15:45 Gaia lessons learned

Although the Gaia mission is still very much alive and still has its most important data releases coming up in the future, the spacecraft operations have ended, and several successful data releases have already been made. Some important lessons learned can therefore already be drawn. This presentation will highlight a few of these.

Speaker: Jos De Bruijne

16:00 The GaiaNIR mission and the hidden regions of our Galaxy, including the inclusion of RVS and end-of-mission accuracies

Speaker: David Hobbs

16:40 → 17:10 Coffee Break

17:10 → 18:40 Tecnical Challenges

17:10 A huge challenge: onboard and on ground data processing

The Gaia ground segment has proven to be an enormous challenge from the
design, science, technical and managerial points of view. It is expected
that GaiaNIR will observe about eight times more stars than Gaia, and
thus, its data processing will be shattering. From our years of
experience with onboard and onground Gaia data handling, and the lessons
learned, in this talk we will go through the GaiaNIR data pipeline -
from the onboard instrumentation to its catalogue publication. We will
provide some considerations on the onboard data handling requirements,
including compression and downlink, and initial suggestions on the
possible approach and needs for the science ground segment.

Speaker: Dr Jordi Portell de Mora (ICCUB)

17:30 Radial velocity and atmospheric parameter calculations for GaiaNIR

We aim to determine the optimal wavelength region for the GaiaNIR spectrograph to maximize radial velocity and atmospheric parameter precision (Teff, log g, [M/H]) between 800 and 2300 nm. To achieve this, we generated 10,000 synthetic spectra using the BOSZ library, spanning a wide range of stellar parameters, resolutions (R=5000–20,000), and signal-to-noise ratios. Radial velocities were derived by cross-correlating these mock observations with ideal, noise-free templates. We analyzed the statistical scatter and 95th percentile of the velocity residuals to subsequently selected four candidate windows for detailed atmospheric parameter testing.

We further explored the precision of atmospheric parameters, and what abundances are available in the four candidate windows to make our final selection for the wavelength range of the spectrograph. Our results demonstrate that while the 845–885 nm region yields the highest intrinsic precision for most parameters, the 1926–1998 nm window represents the preferred strategic choice. It provides sufficiently precise radial velocities and atmospheric parameters for the mission's key targets—cool stars across a wide metallicity range—while leveraging the reduced extinction of the K-band to probe the dust-obscured structure of the Milky Way.

Speaker: Mészáros Szabolcs

17:50 The GaiaNIR photometry

The photometric measurements of GaiaNIR will extend to the infrared the scientific knowledge of the Galaxy, also adding more stars not detectable by Gaia in the visible domain. This talk will discuss the current proposal and the aspects that need to be considered for the definition of the photometric and spectrophotometric instruments for the GaiaNIR mission.

Speaker: Josep Manel Carrasco Martínez (Institut d'Estudis Espacials de Catalunya)

Thursday 29 January

09:30 → 10:50 IR Astrometry: big science questions (I)

09:30 Exploring the Galactic Centre: Opportunities and Challenges with Gaia-NIR

The Galactic Centre is a key environment for understanding how the Milky Way formed and evolved, and for studying the inner regions of spiral galaxies. However, extreme extinction and stellar crowding make Gaia effectively blind to its central parsecs. Near-infrared surveys such as GALACTICNUCLEUS and VVVX-Galcen are revealing the stellar populations there, but their 3D structure and formation history remain uncertain. A future Gaia-NIR mission could provide a direct view of these heavily obscured regions. In this talk, I will review the current state of the field, outline the major open questions, and discuss the potential role and limitations of Gaia-NIR in advancing our understanding of the Galactic Centre. I will also highlight its synergy with ongoing near-infrared surveys.

Speaker: Dr Francisco Nogueras-Lara (IAA-CSIC)

09:50 Kinematic fractionation of the Milky Way boxy/peanut bulge

The Milky Way (MW) bar hosts a prominent boxy/peanut (B/P) structure, recognised since the COBE mission. Simulations of bar evolution that include ongoing star formation show that the B/P morphology varies across stellar populations due to kinematic fractionation, meaning that stars of different ages originate in different kinematical conditions of the bar/disc and therefore settle onto different orbits, producing population-dependent B/P shapes. The metallicity dependence of the B/P in red clump stars provided the first evidence that this process operates in the MW.

In this talk I will present my results from analysing the spatial distributions of variable stars (RR Lyrae and Miras) that trace different age populations and provide further evidence for the kinematic fractionation of the Galactic B/P bulge. Upcoming infrared astrometric surveys such as JASMINE and GaiaNIR will deliver deeper and more complete coverage of the obscured inner Galaxy, enabling far more precise mapping of the MW bar and B/P structure across stellar populations. Combined with improved theoretical modelling, these data will significantly advance our understanding of the MW bar’s dynamics and evolutionary history.

Speaker: Marcin Semczuk (Institut de Ciències del Cosmos, Universitat de Barcelona)

10:10 A GaianIR-aided view of the properties of Local Group dwarf galaxies

As the smallest galaxies and the most dark matter dominated ones that we can observe, Local Group dwarf galaxies are widely considered as precious systems to shed light on the processes that drive galaxy formation and evolution at small halo masses.

Nonetheless, the majority of them are found in the surrounding of a much larger system, i.e. the Milky Way or M31; this makes the knowledge of the orbits around the host a crucial piece of information for investigating the role of environment in shaping the dwarf galaxies' observed properties. In addition, this type of information can also be used to improve our understanding of the host itself, e.g. its dark matter halo mass.

In this talk I will present the results of recent works based on Gaia data and discuss how the existence of Gaia-NIR could improve on those determinations.

Speaker: Giuseppina Battaglia

10:30 Advancing XMC kinematics with GaiaNIR

GaiaNIR will dramatically advance studies of the Clouds (LMC and SMC) by delivering two key improvements in astrometric precision and coverage. First, its extended time baseline will sharpen proper motions for the 15–20 million LMC and SMC stars already observed by Gaia. Second, its near-infrared sensitivity will enable the detection of large new stellar samples in heavily dust-obscured inner regions, such as the LMC bar. Together, these capabilities will uncover previously inaccessible internal kinematic structures and refine dynamical models built on the foundation of Gaia.

Speaker: Óscar Jiménez-Arranz (Lund University)

10:50 → 11:20 Coffee Break

11:20 → 13:00 IR Astrometry: big science questions (II)

11:20 Relativistic modelling for next-generation astrometry

The increasing accuracy of the astrometric parameters expected of modern astrometric catalogs raises the question of to which extent subtle relativistic effects included in astrometric models are needed. The most interesting effect for astrometry is gravitational light deflection: according to general relativity, massive bodies bend the light rays on their way from a source to the astrometric satellite. In particular observations, the deflection angle due to the giant planets of the Solar System may amount to several milliarcseconds. However, an astrometric mission makes many observations of each source, and the deflection angle could be large for a few observations but very small in the remaining ones. Moreover, with increasing number of observed sources (Gaia with 2 billion vs. GaiaNIR with up to 50 billion sources), the number of observations affected by such 'rare' deflection effects will increase. Therefore, it is important to check how large the errors in the astrometric parameters would be if light deflection effects were not taken into account in astrometric models.

In this talk, we consider the example of Gaia and show the errors that would arise in the astrometric parameters when light bending effects were not included in the Gaia Relativity Model. We then compare these effects to expected astrometric accuracy levels in Gaia or GaiaNIR. This allows us to determine if the magnitude of the errors is actually comparable to the accuracy levels we are reaching in Gaia-like space astrometry missions. Along these lines, we also discuss the role that microlensing events by stars in the Galaxy or subtle deflections by other structures such as the asteroid belt may play in reaching an astrometric noise limit, that is, a limiting accuracy in the astrometric parameters which could not be surpassed due to practical limitations, namely the impossibility to control every deflecting body individually. This is particularly relevant for GaiaNIR, which aims to observe many more sources than Gaia and improve the astrometric accuracy for at least some parameters like proper motions.

Finally, we briefly discuss the interrelation between the Celestial Reference Frame and GaiaNIR astrometry.

Speaker: Gabriel Rodríguez Moris (Lohrmann Observatory, Technische Universität Dresden)

11:40 Low-Mass Stars in the GaiaNIR Era: Opportunities and Challenges

Low-mass stars and brown dwarfs (M, L, and T types) dominate the stellar population of the Milky Way and are key to understanding Galactic structure and evolution. Their optical faintness and location in highly extincted regions limit current astrometric surveys. Gaia has revolutionized our view of nearby low-mass stars through precise astrometry and photometry, but its sensitivity decreases sharply for the coolest and reddest objects. Infrared surveys such as VVV and VVVX have extended detections into highly extincted regions, though their astrometric precision is lower than that of Gaia. GaiaNIR will overcome these limitations by extending high-precision astrometry into the near-infrared, enabling a complete census of low-mass stars and brown dwarfs, improved kinematics in dusty regions, and refined constraints on the low-mass end of the initial mass function. Tackling NIR calibration, cross-wavelength consistency, and multi-epoch integration will be crucial to fully exploit GaiaNIR and achieve a complete view of low-mass stars and brown dwarfs.

Speaker: Ms Miriam Cortés Contreras (Universidad Complutense de Madrid)

12:00 The White Dwarf Potential of a Gaia–NIR Mission

White dwarfs are the most common stellar remnants and are widely used as reliable cosmic chronometers, providing important insights into the evolution and history of the Galaxy. Observations in the near-infrared (NIR) open unique opportunities, including the detection of circumstellar disks and substellar companions, as well as studies of the composition of accreted extrasolar planetary material. NIR also enables the characterization of the coolest and oldest white dwarfs in the thin/thick disc and halo, where distinguishing hydrogen- and helium-dominated atmospheres from optical data alone becomes challenging. All-sky NIR astrometry, with the accuracy and coverage of a Gaia-like mission, could provide valuable insights from white dwarfs, helping to refine our understanding of Galactic evolution, probe the oldest and faintest populations, improve age constraints, reveal binaries, and explore the remnants of planetary systems across the Milky Way.

Speaker: Santiago Torres Gil (Universitat Politècnica de Catalunya)

12:20 Unveiling the dusty realm of massive stars with GaiaNIR

Massive stars play a key role in shaping the structure, dynamics, and evolution of the Galaxy, yet a large fraction of its youngest population remains hidden from optical surveys due to heavy dust extinction. These stars are commonly distributed in groups or clusters, which are often part of star-forming complexes. These regions are characterized by strong infrared emission from the heated interstellar dust, in which their newly born populations of massive stars are embedded. Near-infrared astrometry, as envisioned for a GaiaNIR-like mission, would provide unprecedented access to these obscured environments, enabling accurate distances and proper motions for highly obscured massive stars, young clusters, and OB associations across the Galactic disk and inner regions. In this talk, I highlight key science cases on high-mass stars that uniquely benefit from near-infrared astrometry, and illustrate how a GaiaNIR mission could transform our understanding of massive star formation and early stellar evolution in the dusty Milky Way.

Speaker: Sara Berlanas

12:40 The impact of GaiaNIR on future exoplanet science

GaiaNIR has the potential to significantly advance exoplanet science. By extending high-precision astrometry to cooler and more obscured stars, it would broaden the range of both stellar and planetary environments accessible to astrometric planet detection. Combined with Gaia, this new instrument would provide a decades-long astrometric baseline, enabling the discovery and mass measurement of long-period giant planets that other methods cannot access, enabling thereby the detection of Solar-System analogues. Improved stellar parameters from GaiaNIR would enhance the characterization of known exoplanets and strengthen synergies with missions such as PLATO, Ariel, and JWST. GaiaNIR would thus play a central role in shaping future exoplanet studies.

Speakers: Juan Carlos Morales (ICE-CSIC), Manuel Perger (ICE-CSIC)

13:00 → 15:00 Lunch break

15:00 → 16:30 Industry

15:00 Round table with industry

Speaker: IDOM, SENER, AISTECH, AVS, DAPCOM Confirmed

16:30 → 17:00 Coffee Break

17:00 → 18:30 IR Astrometry: big science questions (III)

17:00 Present with Gaia and Future with GaiaNir in the bodies of the solar system

The Gaia mission has revolutionized our understanding of the Solar System by providing unprecedented astrometric and photometric data for small bodies, despite not being originally designed for this purpose. To date, Gaia has delivered high-precision astrometry for over 150,000 asteroids and photometric measurements for tens of thousands of objects, along with reflectance spectra for approximately 60,000 asteroids in the visible range. These achievements have opened new avenues for studying asteroid taxonomy, rotational properties, and phase curves. However, Gaia’s capabilities are limited to the optical domain, leaving the near-infrared (NIR) region largely unexplored from space.
GaiaNIR represents a transformative opportunity to extend Gaia’s legacy into the NIR, covering wavelengths between 0.8 and 2.5 μm. This spectral range includes diagnostic absorption features of silicates (near 0.9 and 2.0 μm), hydrated minerals, and volatiles such as water ice (around 1.5 and 2.0 μm), as well as providing critical information on continuum slopes. These measurements are essential for disentangling compositional classes within the asteroid belt and for probing the distribution of primitive and thermally altered materials. While a single broad NIR filter would enable improved phase-curve studies and rotational characterization, the real scientific breakthrough lies in spectroscopic capability. Low-resolution spectra across this range would allow robust taxonomic classification and compositional mapping, complementing ground-based surveys and addressing key questions about Solar System formation and evolution.
GaiaNIR’s expected sensitivity, assuming performance comparable to Gaia, would enable characterization of objects down to absolute magnitude Hr ≈ 17, corresponding to diameters of several kilometers in the main belt. This complements the Rubin Observatory’s LSST, which will complete the inventory of main-belt asteroids down to Hr ≈ 20 (∼1 km), and surpasses the spectrophotometric capabilities of missions like Euclid. By combining GaiaNIR’s NIR spectroscopy with LSST’s deep optical survey, we can achieve an unprecedented multi-wavelength dataset for hundreds of thousands of small bodies, enabling studies of space weathering, thermal evolution, and volatile retention across diverse populations.
In this presentation, we will review Gaia’s contributions to Solar System science in the visible domain and outline the scientific objectives of GaiaNIR. We will discuss its potential to characterize asteroid composition, constrain dynamical families, and identify reservoirs of volatiles, as well as its synergy with upcoming surveys. GaiaNIR will not only fill a critical observational gap but also provide a cornerstone for comparative planetology, linking small-body populations to the processes that shaped the early Solar System

Speakers: Rene Duffard (Instituto de Astrofísica de Andalucía - CSIC), Dr Alvaro Alvarez-Candal (IAA-CSIC)

17:15 GaiaNIR Photometry and the Census of Unresolved Binaries

Precise Gaia astrometry and photometry have enabled large-scale studies of unresolved binaries across the Milky Way. However, most existing (spectro-)photometric techniques based solely on these data remain primarily sensitive to high mass-ratio systems (q ≳ 0.6). In a recent pathfinder study we demonstrated that incorporating near- and mid-infrared photometry—such as from 2MASS and WISE—significantly enhances the detectability of low-q binaries. The exquisite deep all-sky photometry from GaiaNIR will therefore be transformative, enabling a much more complete census of binary populations in the Galaxy and offering new constraints on the processes governing star formation and dynamical interactions.

Speaker: Sagar Malhotra (IEEC-ICCUB)

17:30 Massive young clusters in the Milky Way

Massive young clusters, with stellar populations approaching or exceeding ten thousand solar masses, are formidable laboratories to study stellar properties and evolution. On the one hand, they contain so many stars of any given type that they permit statistically robust tests of stellar properties, with samples of the same age and composition. On the other, their upper main sequences are sufficiently populated to probe short-lived but crucial evolutionary phases and allow the study of the effects of rotation and binary interactions.
Until recently, it was assumed that such clusters were very rare or even absent in the Milky Way. Recent developments, however, have shown that they are much more common, although there are strong reasons to believe that most of them are hidden in the inner regions of the Milky Way, obscured from view by interstellar extinction and, most importantly, extreme contamination by the field.
I will review the properties of known massive young clusters in our Galaxy and summarize the empirical constraints they provide on high-mass stellar evolution. I will then discuss the observational limitations that currently prevent a complete census of these systems. Finally, I will present the reasons why we can be certain that a near-IR Gaia would give us a large population of these objects. Such a sample would allow us to trace their properties as a function of environment and metallicity, offering a powerful tool to understand star formation and massive star evolution along cosmic history.

Speaker: Ignacio Negueruela (Universidad de Alicante)

17:45 GaiaNIR: Transforming our view of star and planet formation

Gaia has transformed our view of the Milky Way, and a near-infrared successor, GaiaNIR, promises an equally profound revolution in our understanding of how stars and planets form. GaiaNIR will provide, for the first time, homogeneous and precise all-sky astrometry down to the lowest-mass end of the initial mass function, crucial for identifying brown dwarfs and free-floating planets members of young star clusters. Estimating the fraction of substellar objects, their multiplicity (through astrometric, photometric, and spectroscopic variability), and their disk fraction (through NIR photometric excess) is crucial for constraining their formation theories. GaiaNIR will also see through the dust-obscured environments where the earliest phases of star formation occur, providing an unprecedented view of deeply embedded protostars, including proto–brown dwarfs for which astrometry is key to assess their nature. NIR spectroscopy, in addition to being decisive in discarding potential background contaminants, will trace accretion (including episodic accretion in young stars) and outflows through key hydrogen and metal line diagnostics. High-precision astrometry and spectroscopy of newborn stars will be crucial for tracing the dynamical evolution of young star clusters, revealing how gas dispersal affects stellar motions and the early evolution of clusters. Together, these capabilities will establish GaiaNIR as a transformative mission for star and planet formation science.

Speaker: Núria Miret Roig (Universitat de Barcelona)

18:00 Cosmological Simulations for GaiaNIR Studies of the Local Group

The upcoming GaiaNIR mission will provide unprecedented proper motion measurements for stars across the Local Group, extending Gaia’s capabilities into the near-infrared and enabling the inclusion of stars previously obscured by dust. This will improve orbit determinations for the Milky Way’s satellite dwarf galaxies, and neighboring galaxies such as M31 and M33. In this context, cosmological simulations of the Local Group offer a critical framework to interpret the new data, connect observed dynamics to galaxy formation histories, and place individual systems in a broader cosmic environment.
I will discuss the requirements and characteristics of simulations that are particularly well suited to complement GaiaNIR. High-resolution simulations capable of resolving satellite dwarf galaxies and their stellar halos can link observed dynamics to infall times, tidal interactions, and assembly histories. Such simulations can help constrain the mass distribution of the Milky Way and the total Local Group, and predict the fate of major systems such as M31, M33, and the LMC.
GaiaNIR’s near-infrared sensitivity will improve star member selection in dwarf galaxies, better distinguishing them from Milky Way foreground, and potentially revealing new low-mass satellites or stellar overdensities near the Galactic disc. I will explore how simulations can guide the interpretation of these discoveries, including predictions for previously undetected satellites and signatures of tidal stripping.
By combining the enhanced observational capabilities of GaiaNIR with tailored cosmological simulations, we can unlock a richer understanding of the Local Group beyond the Milky Way, placing its formation and evolution within a cosmological context.

Speaker: Isabel Santos-Santos

18:15 Studying the Milky Way stellar halo and its stellar stream with Gaia-NIR

I will present how the improvement in astrometry provided by Gaia-NIR for stars in the outermost component of our Galaxy, the stellar halo, will allow us to better constrain the formation history of the Milky Way and the distribution of dark matter. In recent years, several studies have shown that the halo is out of equilibrium and strongly perturbed, in particular due to the infall of the Large Magellanic Cloud. Understanding these perturbations requires high-precision six-dimensional phase-space information of halo stars, which Gaia-NIR will deliver. I will also show how Gaia-NIR will improve the study of stellar streams, both in the halo and the disc. These streams can be used to anchor the Galactic potential, probe its granularity, and reveal the population of dark matter subhaloes orbiting our Galaxy. In the disc, the near-infrared data will make it possible to trace streams from disrupted open clusters, providing constraints on the evolution of the bar and spiral arms, as well as on streams passing near the Galactic center, offering a more complete 3D view of the Milky Way’s mass distribution.

Speaker: Guillaume Thomas (IAC/ULL)

Friday 30 January

09:30 → 10:50 GaiaNIR: request for simulations

09:30 The GaiaNIR simulator and BGM

Simulations are a cornerstone in the preparation and design of any space
mission. In the case of GaiaNIR, these simulations are critical for estimating the total number of detectable sources, which is expected to significantly exceed the current Gaia catalogue. Such data is essential for refining the mission's observation strategy and finalizing the instrument's technical specifications.
We summarize the work already conducted, specifically the star counts
estimated for various wavelength ranges using Besançon Galaxy Model (BGM)
included in the Gaia simulator. Furthermore, we present new tools and
methodologies designed to enhance the precision of these estimates,
accounting for the unique challenges of near-infrared detection and stellar crowding.

Speaker: Eduard Masana

09:50 The JASMINE Astrometric fleXible Block Iterative Solver (JAXBIS): concept and verification

The upcoming Japan Astrometry Satellite Mission for Infrared Exploration (JASMINE) will provide proper motions and parallaxes for the highly obscured and reddened stars in the central-most parts of the Milky Way, which could help disentangle the origin of the different components that co-exist in the inner-most ~200pc. Since optical wavelengths are blocked by dust, JASMINE observes in the near infrared, a band for which high-precision astrometry is just becoming feasible. As such, the data reduction will require extensive testing, assessing the performance of our models of the optics and detectors against different foreseeable scenarios like periodic thermal fluctuations, permanent deformations of the frame, or chromatic effects. We have designed an iterative Least Squares solver that can process billions of observations, millions of parameters, while relying on auto-differentiation to bypass the need to recalculate the analytical derivatives of our changing calibration models. In this contribution, I will present in detail our novel software and show its potential with the results obtained from simulated data. Thanks to its use of auto-differentiation and unique algorithmic structure, it is highly scalable and adaptable, making it very easy to adopt by other missions. The experience we gain deriving NIR astrometry of the crowded Galactic Centre will certainly be, in several aspects, to great utility for Gaia NIR.

Speaker: Pau Ramos (NAOJ)

10:10 Javalambre surveys as pivotal hubs for data management and scientific exploitation in the GaiaNIR era

GaiaNIR will not only need advanced instrumentation, but also survey-driven infrastructures able to handle very large and complex data sets. The Javalambre wide-field surveys J-PLUS and J-PAS, led by CEFCA and carried out at the Observatorio Astrofísico de Javalambre (OAJ), are natural precursors in this sense. They already deliver well-calibrated images, catalogues and value-added products over thousands of square degrees. By the time GaiaNIR becomes operational, J-PAS will be completed, providing optical spectrophotometry at R≈60 for several hundred million stars down to r≈22. Combined with Gaia astrometry and photometry, this dataset will significantly extend and complement the scientific reach of GaiaNIR, especially for studies of Galactic structure and the Local Group.

A central element is CEFCA’s UPAD data centre, a survey-oriented, scalable infrastructure that manages the full data flow: raw data ingestion, automatic reduction pipelines, quality control, archiving, public data releases and VO-compliant access. The experience gained with J-PLUS and J-PAS in operating a high-throughput survey facility, processing large data volumes and delivering science-ready catalogues can be transferred directly to GaiaNIR. This includes support for simulations, survey design and optimisation, data processing and cross-calibration between optical and near-IR bands, as well as strategies for target selection in crowded and dusty regions. Altogether, the Javalambre surveys and their data centre provide a powerful framework for GaiaNIR data management and for maximising its scientific impact on Galactic and Local Group astronomy.

Speaker: Borja Anguiano (Centro de Estudios de Fisica del Cosmos de Aragon (CEFCA))

10:30 Modelling the MW exoplanet population

The number of detected exoplanets increased significantly in the last decade, finally allowing us to study the exoplanet population from a Galactic point of view. But the detected population is not completely representative of the entire exoplanet population, due to observational biases.
Aiming to simulate a realistic Galactic exoplanet population, we combine planetary formation models and our best knowledge of stellar and exoplanet statistics. We present the process we developed to generate a synthetic exoplanet population, from any given stellar population, considering the relation between exoplanet occurrence rates and host-star properties.
In order to test our generated exoplanet population, we simulated exoplanets in the Kepler field of view, reproducing the selection function of Kepler’s exoplanet census. Comparing our simulated “detectable” planets and the exoplanets detected by Kepler, we identified the model parameters to refine to obtain an even more realistic simulation (e.g. the absence of the observed radius gap).
We also generate exoplanet populations in different regions of the simulated Galaxy. Our results suggest that terrestrial planets, even if they are largely underrepresented in current detections, are extremely abundant in all regions of the Galaxy.
We apply the same exoplanet creation process to the future PLATO long-duration phase fields to estimate the number of detectable planets and compare our estimate with existing studies, and will extend it to other future missions in the future, like Gaia NIR.

Speaker: Chloé Padois (Universitat de Barcelona - ICCUB)

10:50 → 11:20 Coffee Break

11:20 → 12:40 GaiaNIR Sinergies

11:20 The future Roman Galactic Plane Survey and HAYDN - Synergies with GaiaNIR

I will briefly present 2 upcoming space missions relevant to GaiaNIR: Nancy Grace Roman's recently approved Galactic Plane Survey, and the HAYDN mission.

The Nancy Grace Roman Space Telescope is currently on track to be launched in late 2026. It will perform a deep (Ks~24 mag) Galactic Plane Survey in the near-infrared whose main objective is to create a high-resolution (~0.1 arcsec) map of the Inner Galaxy. The observations will be conducted at two epochs separated by ~5 years, allowing for relative proper motions - these will potentially be very useful also for GaiaNIR astrometry.

HAYDN, on the other hand, is one of the ten mission concepts proposed to ESA’s M-class call (M8) after its Step-1 selection. Its mission is to revolutionise our understanding of stellar evolution through high-precision, space-based asteroseismology in dense stellar fields, including clusters. HAYDN’s science cases also include Galactic evolution and exoplanetary science. Spain is currently the second-largest contributor to the project, with active participation from several national institutes and universities. There is still room for active participation in the science preparation activities from our community - also with regards to synergies with GaiaNIR.

Speaker: Friedrich Anders (Universitat de Barcelona)

11:40 The Euclid mission in the context of the GAIA NIR mission

ESA´s Euclid mission was launched from Cape Cañaveral in
Florida in July 2023.
It is a wide-field space telescope with two instrument, the visual
imager (VIS) and the near-infrared imager and slitless spectrograph
(NISP). Euclid is carrying out a 5-year survey of the extragalactic sky
to study the geometry of the Universe.
It has already produced two public data releases, namely the Early
Release Observations (ERO) and the Quick data release 1 (Q1). Deep wide
field multi-color images and catalogs were provided in the the ERO
release, including low-galactic latitude regions in well-known nearby
star-forming regions and very young open clusters. The Q1 release
consisted of a first glimpse of the Euclid Deep Fields that are going to
be observed repeatedly throughout the mission. Preparation of the major
data release number 1 (DR1) is underway as it is scheduled to become
public in the fall of 2026. This presentation will deal with the Euclid
performance and limitations, the current status and future plans,
particularly in the context of synergies with Gaia NIR. Some examples of
big science questions in the realm of Substellar Astrophysics will be
discussed.

Speaker: Eduardo Martín

12:00 Exploring Synergies Between the Rubin Observatory/LSST and GaiaNIR

The Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) will provide an unprecedented view of the dynamic optical sky, combining deep, wide, and multi-epoch observations of billions of sources over ten years. Its photometry and astrometry open opportunities to complement and enhance the capabilities of future missions such as GaiaNIR.

In this talk, I will present the key capabilities of Rubin/LSST and highlight some of the major scientific projects currently underway.

I will also discuss potential synergies between Rubin/LSST and GaiaNIR, focusing on how combining optical and near-infrared observations could expand scientific opportunities and foster collaboration between the two communities.

Speaker: Laura Toribio San Cipriano (CIEMAT)

12:20 HWO & LIFE

In the "Final recommendation from the Voyage 2050 Senior Committee", an ESA reference document similar to a NASA Decadal Survey, the Senior Committe considered that for the "From Temperate Exoplanets to the Milky Way" theme, a mission on the Characterisation of Temperate Exoplanets had a higher scientific priority. Should it be determined that this is not feasible, the Senior Committee recommended rather a focus on the Galactic Ecosystem with Astrometry in the Near-infrared. In the current landscape of on-going space mission development in Europe, the NIR astrometric mission is of course Gaia-NIR, while the temperate exoplanet characteriser is the Large Interferometer For Exoplanets (LIFE), which might compete with Gaia-NIR for the L5 slot. LIFE grows on the concepts already used by Darwin and Terrestrial Planet Finder-Interferometer. In parallel, NASA is developing its Next Great Observatory, dubbed Habitable Worlds Observatory (HWO), which may have important contributions from ESA (such as the POLLUX spectropolarimeter), CSA and even JAXA. China is also developing its own exolife-searching space mission, Tianlin. I will briefly summarise the status and basic properties of HWO, LIFE and Tianlin.

Speaker: José A. Caballero (Centro de Astrobiología CSIC-INTA)

12:40 → 13:30 Next steps: actions for future Spanish enrolments

Round table