Laboratório Nacional de Astrofísica

Abstract Stellar populations in the central regions of disc galaxies provide key constraints on their formation and secular evolution. We investigate the properties of young stellar populations in the centres of nearby barred galaxies from the TIMER survey, using four stellar population models, two based on empirical stellar libraries (MILES, X-Shooter) and two on theoretical libraries (Starburst99, HR-pyPopStar), complemented by independent gas-phase metallicities from emission-line diagnostics. The inferred stellar metallicities depend strongly on the adopted model. Measured as the 5th-to-95th percentile spread across the three galaxies analysed in detail, the empirical libraries recover variations of 1.11 and 0.98 dex, whereas the theoretical ones return 0.40 and 0.49 dex; the gas in the same regions spans 0.49 dex. Gas metallicities are indeed lower in the central star-forming regions, but the amplitude of that depression (about 0.3 dex in NGC 1097) exceeds what bar-driven inflow of disc gas can account for, given typical abundance gradients in literature. The age–metallicity relations consistently reveal two distinct components: an older population consistent with a self-enrichment scenario, and a younger population formed from gas inflows with a different chemical enrichment history. The empirical libraries produce a monotonic decline of metallicities from old to young populations, which would require a sustained inflow of metal-poor gas outpacing its own enrichment. The theoretical libraries instead recover a young component whose metallicity departs from the older populations only at the most recent ages and by a few tenths of a dex, compatible with a single dilution episode. Our results demonstrate that model choice critically affects inferred metallicities, with models based on empirical stellar libraries recovering age–metallicity relations that demand physical conditions the gas measurements cannot sustain.

Abstract Planet formation in the Galactic thick disk is expected to be inefficient—low solid reservoirs, short disk lifetimes, and harsh irradiation environments should conspire to inhibit the assembly of planetary bodies—yet, planets are there, and they are stranger than we expected. Here, we present a homogeneous characterization of 32 exoplanetary systems orbiting chemically and kinematically confirmed thick disk stars, combining new detections with a systematic reassessment of archival systems, increasing the total number of exoplanets orbiting thick disk stars to 66. When planets form in the thick disk, a notable fraction are giants and move on more eccentric orbits than their thin disk counterparts—two results that challenge standard disk-evolution models. However, this should be interpreted with caution given detection biases and sample size. We also report TOI-1927 b and TOI-2643 b, the first puffy, low-density giant planets known to orbit thick disk stars, unexpected in old, metal-poor environments where planets should cool and contract efficiently. Together, these findings reveal an early Milky Way far more hospitable to planetary diversity than its harsh conditions would initially suggest.

Abstract The large amount of ground-based photometric measurements of η Carinae obtained since 1940 have remained problematic for quantitative modeling due to the blending of flux from the stellar core and the surrounding circumstellar nebula. In the era of the Hubble Space Telescope (HST), spatially resolved imaging and spectrophotometry have enabled disentanglement of these components, allowing recovery of the stellar core V -band brightness from ground-based observations. We isolate the V -band fluxes of the stellar core and nebula using 1999–2020 HST (Advanced Camera for Surveys and Space Telescope Imaging Spectrograph) observations, and use these to calibrate coeval ground-based photometry. The main finding is an orbital light curve with an amplitude Δ m ≈ ±0.2 mag, many times higher than that modeled by ellipsoidal deformation of the primary. The observations suggest that Roche lobe overflow starts at −75 days before periastron in coincidence with the start of rising in the orbital light curve, and remains for 150 days. An expanding (and afterward dissipating) gas cloud reflecting the light from the primary would explain the observed large amplitude of the orbital light curve. A sharp periodic photometric peak occurs at ∼−18 days from the periastron. It is followed by a broad minimum around the superior conjunction of the secondary ( T 0 + 5.2 days), which we interpret as a partial eclipse of the ejected material, in coincidence with the shallow minimum in X-rays, which also has been attributed to an eclipse.

Context . Spectroscopic monitoring surveys have shown that the magnetic cycle alters the photospheric structure of the Sun, perturbing the formation of molecular lines. In parallel, the study of globular clusters (GCs) has remained centred on the multiple stellar populations (MPs) conundrum, a phenomenon defined – most notably – by the anti-correlation between CH and CN molecular bands, serving to distinguish between first-population (1P) and second-population (2P) stars. Aims . Since these molecular transitions are intrinsically sensitive to photospheric conditions, we investigated whether stellar magnetic activity can induce spectroscopic variations consistent with the signatures traditionally utilised to disentangle 1P and 2P populations. Methods . We bridged the stellar and solar domains by applying standard spectroscopic index analyses – routinely used to identify MPs in clusters – to a decade-long dataset of disc-integrated high-resolution solar spectra. We systematically monitored the behaviour of the CH and CN molecular bands as a function of the solar magnetic cycle. These observational results are further complemented by first-order magnetohydrodynamic (MHD) simulations to evaluate how these signatures scale with increased magnetic activity. Results . We demonstrate that the disc-integrated solar spectrum exhibits a distinct CH/CN anti-correlation driven by the magnetic cycle. Our simulations indicate that these variations in molecular line formation scale significantly with increased magnetic filling factors, rendering them, in principle, capable of reaching amplitudes comparable to the spectroscopic spreads observed between 1P and 2P stars in GCs. Conclusions . While the broader implications of our discovery of a CH/CN anti-correlation in the single-star Sun remain to be fully elucidated, our results suggest that the spectroscopic and photometric anomalies defining the MP conundrum may be physically linked to a differential spectral response to varying degrees of surface magnetic coverage. The emerging mechanism depends on the intrinsic magnetic state of the star – distinguishing relatively active from relatively quiescent stars – rather than the existence of a magnetic cycle itself. Surface magnetism offers a novel physical framework that may provide new insights into the origin of MPs and clearly warrants future exploration.

We present a comprehensive reanalysis of two star-planet systems: TOI-4438, an M3.5V star hosting a mini-Neptune in a 7.4-day orbit, and TOI-442, an M1V star with a 4-day period planet located within the hot Neptune desert. Both systems were originally identified as transiting planet candidates by the Transiting Exoplanet Survey Satellite (TESS) and subsequently validated through the radial velocity (RV) method. Our work incorporates new TESS transit data and high-resolution spectroscopy from the SPIRou near-infrared spectropolarimeter. We detected a persistent and relatively strong Zeeman signature in TOI-442, while TOI-4438 exhibits weaker and intermittent magnetic activity, and we inferred the stellar rotation periods of both stars from the variability of the longitudinal magnetic field. We jointly fit photometry and RV models for each system. For TOI-4438 b we combined archival CARMENES data with 81 SPIRou observations and five TESS sectors. This yielded a refined planetary mass of M p = 4.11 +0.40 −0.38 M ⊕ and a radius of R p = 2.40 +0.09 −0.10 R ⊕ , consistent with the previous estimate within 1.1 σ while improving by 53% the precision on the mass and 22% on the radius. For TOI-442 b, we added 29 SPIRou RV measurements to an extensive archival dataset, significantly extending the temporal baseline. Incorporating this with a new TESS sector, we tighten the constraints on the planetary mass to M p = 28.38 +0.77 −0.73 M ⊕ and radius to R p = 4.25 +0.10 −0.08 R ⊕ , which agrees with the previous values within 1.5 σ and improves the precisions by 46 and 67%, respectively. We found no clear signs of additional planets in the currently available RV data, although we detected a single-transit event in the TOI-4438 light curve. We compared various RV models and found that those accounting for stellar variability-induced signals yield improved constraints on the planetary parameters.

Abstract We present results from 28 stellar occultations by the large trans-Neptunian object (50000) Quaoar registered between 2018 and 2025. By performing a joint analysis of this occultation dataset, along with nine other published events, we were able to fit an oblate ellipsoid shape, with equatorial semiaxes a and b of 566 . 1 − 2.2 + 2.5 km, and a polar semiaxis, c , of 511 . 2 − 3.7 + 3.6 km. It provides an equivalent volumetric diameter of 1094.4 ± 4.6 km and polar oblateness of 0.097 ± 0.011. Considering an absolute magnitude of H = 2.79 ± 0.35, we derive a geometric albedo of p V = 0.125 ± 0.038. We have derived new upper limits to the surface pressure of a CH 4 atmosphere of 0.15 nbar (1 σ ) and 0.65 nbar (3 σ ). We also provide a table with the 36 new astrometric positions for Quaoar. Using the new system mass derived from Weywot’s orbit around Quaoar, we calculated a density of 1.760 ± 0.109 g cm −3 . Moreover, from the derived size and rotation period (8.8394 ± 0.0002 hr, we calculated that, if Quaoar is in Maclaurin hydrostatic equilibrium state, it would have a density of 1.859 ± 0.200 g cm −3 . This result, within the error bars, is compatible with the value we found. Therefore, this work shows that Quaoar can be a Maclaurin object, being eligible as a dwarf planet.

SPARC4 (Simultaneous Polarimeter And Rapid Camera in 4 bands) is a new instrument for the Pico dos Dias Observatory (OPD). It acquires images with a field of view of 5.7' × 5.7' in four channels simultaneously, whose spectral responses are very similar to the g, r, i, and z bands of the SDSS photometric system. It can be used as a standard imager or as an imaging polarimeter capable of measuring linear and circular polarization. The detectors are frame-transfer electron-multiplying CCDs. SPARC4 has various detector acquisition options from low-noise to fast-reading modes, achieving dead times of around 5 ms in the photometric mode. The images have excellent optical quality, with both photometric and polarimetric modes delivering S/N primarily limited by photon and detector noises. Following its first light in November 2022 and the commissioning throughout 2023, SPARC4 is an OPD facility as of the 2024A semester. This Brazilian initiative is a joint effort of the National Institute for Space Research (INPE) and the National Laboratory for Astrophysics (LNA).

The SOAR Telescope Echelle Spectrograph (STELES) is a high-resolution, near-UV/optical spectrograph for the 4.1 m SOAR Telescope. STELES is a Nasmyth-fed, dual-channel (blue/red), VPH cross-dispersed echelle spectrograph operating in quasi-Littrow white-pupil configuration. The instrument provides simultaneous wavelength coverage from ∼300 to 960 nm at mean resolving powers approaching R ∼ 50, 000 and is optimized for high throughput, particularly in the near-UV. The bench-mounted spectrograph is fed by a dedicated fore-optics system, and is permanently mounted below the Nasmyth platform. Installed and commissioned since August 2025, STELES is currently available for scientific observations. In this work, we present an overview of the instrument design, control and data-reduction systems, and its initial on-sky performance, including measurements of throughput, wavelength calibration, spectral resolution, and representative science observations.

MOSAIC, the wide-field multi-object spectrograph for the Extremely Large Telescope (ELT), is advancing through Phase B2, where subsystem architectures mature toward the Preliminary Design Review. Central to the Front-End channel is the Instrument Core Subsystem (ICOS), which provides the mechanical support, alignment stability, and controlled rotation required by the focal-plane assembly and the GLAO, ORSS, and CALEMOS subsystems. ICOS comprises a steel Static Structure Module interfaced to the Nasmyth platform, a motorized Rotating Structure Module that delivers field -rotation compensation with accuracy better than 0.095 mrad , and a Cable Wrap Module enabling continuous ±180 deg motion. ICOS must include an alignment strategy capable of restoring the optical axis to the sub-100μm level required for injection efficiency and pupil stability. With refined interfaces and a mass current estimated mass of 12.97 t, within the 13.3 t allocation, ICOS is converging toward a robust preliminary design for Phase C.

ECHARPE is a new fiber-fed, high-resolution ´echelle spectrograph for the 1.6-m Perkin & Elmer telescope at the Observat´orio do Pico dos Dias (OPD/LNA), Brazil. Designed as a bench-mounted and environmentally controlled instrument, it delivers broad visible-band coverage (380–900 nm) with a resolving power of R ∼ 50,000, enabling precise radial velocity and stellar abundance analyses. This contribution summarizes the main characteristics and design choices of the instrument, including its optical layout, mechanical architecture, fiber-injection system, and calibration unit. We describe the final construction phase now underway, focusing on the integration of the optical bench, alignment of opto-mechanical assemblies, and implementation of the control and data-acquisition systems. We present first laboratory results, including preliminary spectral measurements, stability tests, and throughput estimates. Commissioning at OPD is planned for late 2026, enhancing the spectroscopic capabilities of the observatory.