Julia Martikainen

Context. Originating from massive stars that have lost most of their hydrogen envelopes, type IIb supernovae are stellar explosions of partially stripped stars. Due to this extensive stripping, their spectra exhibit transitional signatures that bridge the gap between hydrogen-rich (type II) and helium-rich (type Ib) events, making them crucial astrophysical probes for investigating the final evolutionary stages of massive stars. Aims. We aimed to investigate the physical properties and the underlying explosion mechanisms of the type IIb SN 2025aico. Through a comprehensive analysis of early-phase optical light curves and spectroscopic data, we aimed to constrain the fundamental explosion parameters and evaluate the physical state of the event. Methods. We present early multi-band optical imaging and low-resolution optical spectroscopic follow-up observations of the type IIb SN 2025aico, spanning ∼70 days from the explosion. We constrained the properties of SN 2025aico using a hybrid model that combines shock-cooling emission and radioactively powered diffusion, as well as through an analysis of its spectroscopic evolution. We used various approaches to constrain ⁵⁶ Ni mixing from early data and compared our spectra with models to constrain the properties of the progenitor. Results. The explosion epoch of SN 2025aico is estimated to be Modified Julian Date (MJD) 61032.69, while the rise time in the r _M band is 22.30 ± 0.70 days. The peak pseudo-bolometric luminosity in the optical bands is L _opt = (4.07 ± 0.10)×10 ⁴¹ erg s ⁻¹ . The fitting yields a moderate to relatively low ⁵⁶ Ni mass of M _Ni = 0.033 _−0.004 ^+0.006 M _⊙ and an ejecta mass of M _ej = 2.79 _−0.18 ^+0.21 M _⊙ . The photospheric velocity near the bolometric peak, measured from the Fe II λ 5169 line, is 6450 ₋₁₆₀ ^+0.180 km s ⁻¹ . The derived envelope properties suggest a compact He-star progenitor possessing an H-rich envelope of M _env ≈ 0.02 M _⊙ and a radius of R _env ≈ 6–10 R _⊙ . Conclusions. The derived physical properties of SN 2025aico indicate an origin from a moderate-mass, stripped He-star in a compact binary system, characterized by a minimal residual hydrogen envelope. The explosion itself demonstrates weak to moderate ⁵⁶ Ni mixing throughout the ejecta.

Polarization at millimeter wavelengths provides a powerful diagnostic of dust grain properties in protoplanetary disks. Standard models based on solid spherical grains often struggle to reproduce the observed polarization fractions and morphologies in systems where self-scattering is expected to dominate. We investigate the impact of grain morphology on polarized millimeter emission by comparing models that adopt solid spherical grains with models that employ solid irregular hexahedral particles drawn from the TAMUdust2020 database. Both grain populations share identical size distributions, enabling us to isolate the effects of geometry while preserving the same internal structure and material density. We explore three optical-depth regimes—optically thick, optically thin, and an intermediate hybrid case—to assess how grain morphology modifies the polarization structure under different conditions. For size distributions with a max ∼ λ / 2 π , where scattering-induced polarization is expected to peak, we find that the polarization morphology and fraction are nearly indistinguishable between spherical and irregular grains. The primary quantitative difference is an enhancement of the scattering opacity by up to a factor of ∼2.5 for irregular particles, implying that disk dust masses inferred under the assumption of spherical grains may be systematically overestimated. Irregular grains also suppress the polarization reversal predicted by Mie theory at large size parameters ( x > 1). Nevertheless, modifying grain geometry alone is insufficient to reproduce the observed polarization fractions within a pure self-scattering framework. These results suggest that additional physical effects, such as dust porosity, warrant dedicated investigation.

We study the effects of using the optical properties of irregular hexahedral grains in photoionization models of circumstellar nebulae around evolved stars. Dust opacities for the irregular grains were obtained from the scattering properties available in the TAMUdust2020 database and these were implemented in the spectral synthesis code cloudy. A sample of photoionization models that use opacities from both spherical and irregular hexahedral grains across a standard MRN size distribution (0.005-0.25 μm) was produced. We consider the optical properties of graphite, amorphous carbon and silicate dust grains and find that differences between the model nebula continua calculated using spherical and irregular dust grains increase with the grain size, especially for graphite. In particular, we find that the luminosities at the infrared peak for the hexahedral grain models can be up to 60% higher than those from the equivalent spherical grain models for the largest grains. This result suggests that traditional spherical grain assumptions may lead to an overestimate of the dust mass in photoionized nebulae.

This study is part of an ongoing project in which we experimentally examine the effect of composition (refractive index) and surface roughness on the scattering matrix elements of a set of well-characterized rough regolith simulants. A set of four cylindrical Mars regolith simulants with controlled degrees of porosity and surface roughness is studied. Photopolarimetric measurements, spanning scattering angles from 94° to 177°, were conducted at a wavelength of 488 nm at the Instituto de Astrofísica de Andalucía Cosmic Dust Laboratory. These results are compared with those previously obtained at 640 nm. The higher absorption of the Mars simulants at 488 nm compared to 640 nm produces a significant effect on all elements of the scattering matrix. The trends previously observed in the diagonal elements of the scattering matrix and in the albedo as a function of surface roughness remain unaffected by the differences in refractive indices at both wavelengths. The comparison with the previous study enables the investigation of sample reddening across the scattering-angle range, with a trend also observed between surface roughness and reddening. Moreover, within our measured angular range, the effect of absorption is consistent with Umov’s law, whereas the effects of surface roughness do not appear to support its validity. Nearly all samples exhibit a shallow negative polarization branch.

. IntroductionAerosol dust particles are an important component in planetary atmospheres, influencing energy balance, thermal structure, weather systems, and remote observations. Despite their importance, radiative-transfer models and climate simulations for planets are often limited by assumptions of oversimplified particle shapes and fixed complex refractive indices for aerosol dust, which hinders the interpretation of observational data. To address this gap, we present an experimentally validated database of aerosol dust optical properties derived from Martian dust analogs. The work combines laboratory measurements with advanced light-scattering modeling and provides a transferable methodology for studying aerosols in a variety of planetary environments.2. Sample Preparation and CharacterizationWe selected three spectrally and mineralogically distinctive Martian dust analogs representative of different Martian terrains: JSC Mars-1, MGS-1, and MMS-2 (see Figure 1). The samples were processed at Instituto de Cerámica y Vidrio (ICV) to produce narrow particle size distributions in the geometric optics domain for the retrieval of complex refractive indices, as well as narrow size distributions representative of airborne dust aerosols for the computation of optical properties. Detailed morphological and compositional characterization was performed using SEM imaging, laser diffraction particle sizing, and X-ray diffraction (XRD) (see Martikainen et al. 2023).Figure 1: The JSC Mars-1, MGS-1, and MMS-2 analogs. 3. Experimental DataDiffuse reflectance spectra were measured from 200 to 2000 nm using a Varian Cary 5000 UV-vis-NIR spectrophotometer for samples with narrow particle size distributions in the geometric optics domain (Martikainen et al. 2023). The scattering matrix measurements at 488 and 640 nm were carried out at the Cosmic Dust Laboratory (CODULAB, Muñoz et al. 2010) of the Instituto de Astrofísica de Andalucía (IAA), covering scattering angles from 3° to 177° using analogs with narrow size distributions representative of airborne dust (Martikainen et al. 2024). The measurements include the phase function (F₁₁), degree of linear polarization (−F₁₂/F₁₁), and, where possible, additional scattering matrix elements (F₂₂, F₃₃, F₃₄, F₄₄). Together, these datasets provide the experimental basis for retrieving the complex refractive indices and computing bulk optical properties for radiative-transfer modeling.4. Light-scattering modelingThe complex refractive indices were retrieved using the SIRIS4 ray-tracing model (Muinonen et al. 2009), which accounts for the irregular shapes of real dust grains. The model was applied to the measured diffuse reflectance spectra and corresponding narrow particle size distributions in the geometric optics domain. In this regime, the scattering behaviour of large particles is highly sensitive to the complex refractive index, allowing it to be reliably constrained from the measurements.Bulk optical properties were computed using the TAMUdust2020 database of irregular hexahedral particles (Saito et al. 2021), based on the retrieved complex refractive indices and narrow size distributions representative of airborne dust. The modeled phase matrices were compared with measurements at 488 and 640 nm to validate both the retrieved complex refractive indices and the hexahedra particle model. The final set of calculated properties includes single-scattering albedo, extinction efficiency, extinction cross-section, asymmetry factor, and phase matrix elements across the 200–2000 nm spectral range.5. Broader ApplicationsWhile the database is based on Martian dust analogs, both the experimental approach and the modeling framework are designed to be transferable. Similar methods can be applied to characterize aerosols in other planetary atmospheres, such as those of Venus or exoplanets. Our work demonstrates the value of combining controlled laboratory measurements with advanced numerical scattering models to improve the realism of aerosol dust optical data. Moreover, our derived optical properties reproduce the key spectral features of observed Martian regolith. This confirms the physical relevance of the results and supports their use in forward modeling and data interpretation.6. ConclusionsWe provide a validated, multi-wavelength database of aerosol dust optical properties derived from Martian dust analogs (Martikainen et al. 2025), intended for use in radiative-transfer modeling and observational retrievals across the planetary sciences. The methodology is designed for adaptation to other planetary atmospheres and dust compositions. The full dataset is available at the Granada-Amsterdam Light Scattering Database (Muñoz et al. 2025).References: Martikainen et al. (2023), ApJS 268; Martikainen et al. (2024), ApJS 273; Martikainen et al.(2025), MNRAS 537; Muñoz et al. 2011, JQSRT 111; Muñoz et al. (2025), JQSRT 331; Muinonen et al. (2009), JQSRT 110; Saito et al. (2021), JAS 78.

Modeling the brightness of a surface consisting of particulate material is a problem we often face in planetary science, but it is also present in many other fields from Earth remote sensing to material science and industrial applications. The forward problem depends on particle sizes, shapes, packing, and the optical properties of the materials. In the inverse problem, we want to estimate some of the mentioned properties from the scattering characteristics of the material.In general, the forward problem can be difficult if the particulate material has rough structure in many size scales including the scale of the wavelength considered, in which case the Maxwell equations need to be solved for the wavelength scale. However, if the particles are large compared to the wavelength, we can employ a geometric optics approximation to calculate average single-scattering properties of the grains in the material, and a radiative transfer approximation to consider the response of the particulate material.We have employed the abovementioned modeling to study the effect of particle size and complex refractive index m=n+ik on the reflected intensity of particulate surfaces. The direct application of this method is the inversion of m, and especially the extinction coefficient k, from reflectance measurements with known particle shapes and sizes.We simulate the forward problem in a grid of input parameters (size, n, and k) and create a library of reflectance values that are integrated over the backward scattering hemisphere of a particulate surface when illuminated directly from above. Particle shape is fixed to a random convex polyhedral shape. Single-particle scattering properties are simulated using the SIRIS[1] geometric optics code, and multiple scattering and the backward hemispherical reflectance with RT-CB[2] code employing only the radiative-transfer part as the coherent backscattering effects are not important here.We present the results of these simulations and show how the received reflectance can be approximated with a simple, logistic-type function with the size parameter of the particles (size in relation to the wavelength) and the extinction coefficient combined into a single parameter, and the real part not having any significant role in this approximation. The analytical approximation can be used for quick inversion of reflectance measurements for the extinction coefficient with known size or to the size with known extinction coefficient [3]. Finally, we present the predictions using this model for mixtures of Mercury-related endmembers created in the ISSI project “Wide-Ranging Characterization of Explosive Volcanism on Mercury: Origin, Properties, and Modifications of Pyroclastic Deposits” led by A. Galliano, and compare to measurements of the mixtures.[1] Muinonen et al. (2009). Light scattering by Gaussian particles with internal inclusions and roughened surfaces using ray optics. JQSRT 110, 1628–1639.[2] Muinonen K, 2004. Coherent backscattering of light by complex random media of spherical scatterers: Numerical solution. Waves in Random Media 14(3), 365-388.[3] Penttilä et al. (2024). Modeling linear polarization of the Didymos-Dimorphos system before and after the DART impact. The Planetary Science Journal, 5(1), 27.

The characterization of dust particles in the Solar System is a fundamental component of planetary science. These particles are present in a variety of environments, including the atmospheres of planets and satellites, comets, or covering the surfaces of planets, moons, and asteroids. The ever-growing number of new exoplanetary systems show that the Solar System is just a particular case in our galaxy. Through the scattering and absorption of stellar radiation, dust particles significantly influence the radiative balance of the corresponding atmosphere. However, their net radiative effect remains one of the major sources of uncertainty in atmospheric modeling. This uncertainty largely stems from a lack of understanding of how stellar radiation is scattered by a cloud of realistic dust particles i.e. the lack of accurate scattering properties for dust and cloud particles. While modeling these properties is straightforward for homogeneous spheres, it becomes highly complex when dealing with irregularly shaped dust particles. Hence, the importance of laboratory astrophysics and in particular the characterization of cosmic dust optical properties for proper interpretation of astronomical observations.Over the last years, the IAA Cosmic Dust Laboratory (IAA-CODULAB) (Muñoz et al., 2011) has generated a substantial collection of high-quality experimental scattering matrices for clouds of randomly oriented cosmic dust analogues. Measurements are conducted at three wavelengths (448 nm, 520 nm, and 640 nm), spanning a wide scattering angle range from 3° to 177°. These datasets are available in digital format through the Granada-Amsterdam Light Scattering Database (scattering.iaa.es) (Muñoz et al., 2025). The database includes the full set of measured scattering matrices along with comprehensive metadata describing the scattering samples, and guidance on how to interpret and utilize the data effectively. The samples presented in the database comprise a wide range of sizes (sub-micron up to mm-sized grains), shapes and compositions. We have recently added the diffuse reflectance spectra of some of our powder samples and, from these spectra, obtained the corresponding refractive indices (200 nm–2000 nm) (Martikainen et al 2023). In this presentation, we will provide an overview of the database and illustrate its application through examples demonstrating how the experimental data can be used to interpret astronomical observations.REFERENCESMuñoz, O.; Moreno, F.; Guirado, D.; Ramos, J. L. ; Volten, H. ; Hovenier, J. W. The IAA cosmic dust laboratory: Experimental scattering matrices of clay particles. Icarus, Volume 211, Issue 1, p. 894-900, 2011. Muñoz, O. Frattin, E.; Martikainen, J. ; Guirado, D. ; Passas-Varo, M. ; Escobar-Cerezo, J. ; García-Izquierdo, F. J. ; Gómez-Martín, J. C. ; Gray, Z. ; Jardiel, T. ; Moreno, F. ; Ocaña, A. J. ; Peiteado, M. ; Gallego-Calvente, A. T. ; Volten, H. Update Granada–Amsterdam Light Scattering Database. JQSRT, 331, id.109252, 2025 Martikainen, J.; Muñoz, O.; Jardiel, T.; Gómez Martín, JC; Peiteado, M; Willame,Y; Penttilä, A; Muinonen, K.; Wurm, G.; Becker, T. Optical Constants of Martian Dust Analogs at UV-Visible-Near-infrared Wavelengths. ApJ Suppl. Series, 268 (2), id.47, 2003

The experimental data base of scattering matrices of three well-characterized Martian dust analogues with narrow particle size distributions representative of Martian dust aerosols is used to check the the suitability of hexahedra model particles to reproduce the scattering behaviour of realistic polydisperse irregular particles at 488 and 640 nm. In general, the hexahedra model performs well. The scattering matrix elements as functions of the scattering angle can be reproduced with good accuracy for particle size distributions that contain small particles; however, the discrepancies increase with increasing particle size due to wavelength-scale surface roughness and internal structure found within large dust grains that are not accounted for by the smooth hexahedra model particles. We further perform sensitivity tests to study the effect of absorption, real part of the complex refractive index, and particle size distribution within the model to understand their contribution to the modelled scattering matrix elements. By using the best-fitting parameters from the sensitivity study, we have created a data base of optical properties that includes bulk extinction efficiencies, single-scattering albedos, asymmetry factors, extinction cross-sections, and phase matrices of the analogue samples from 200 to 2000 nm. The obtained values can be further used in radiative-transfer simulations. This work emphasizes the importance of accounting for the full scattering matrix as information on particle shape, size, and complex refractive index is lost when omitting polarization.

Within the RoadMap project, we investigated the microphysical aspects of particle collisions during saltation on the Martian surface in laboratory experiments. In earlier works, we followed the size distribution of ejected particles, their aerodynamic properties, and aggregation status upon ejection. We now focus on the electrification and charge distribution of ejected particles. We analyzed rebound and ejection trajectories of grains in a vacuum setup with a strong electric field of 100 kV m⁻¹ and deduced particle charges from their acceleration. The ejected particles have sizes of about 10–100 μm. They carry charges up to 10⁵ e or charge densities up to >10⁷ e mm⁻².

We study a magnitude-limited sample of 36 broad-lined type Ic supernovae (SNe Ic-BL) from the Zwicky Transient Facility Bright Transient Survey (detected between 2018 March and 2021 August), which is the largest systematic study of SNe Ic-BL done in literature thus far. We present the light curves (LCs) for each of the SNe and analyze the shape of the LCs to derive empirical parameters, along with the explosion epochs for every event. The sample has an average absolute peak magnitude in the r band of M ¯ r , max = − 18.51 ± 0.15 mag. Using spectra obtained around peak light, we compute expansion velocities from the Fe ii 5169 Å line for each event with high enough signal-to-noise ratio spectra, and find an average value of v ph ¯ = 16 , 100 ± 1100 km s⁻¹. We also compute bolometric LCs, study the blackbody temperature and radii evolution over time, and derive the explosion properties of the SNe. The explosion properties of the sample have average values of M ¯ Ni = 0.37 − 0.06 + 0.08 M ⊙ , M ¯ ej = 2.45 − 0.41 + 0.47 M ⊙ , and E ¯ K = ( 4.02 − 1.00 + 1.37 ) × 10 51 erg. Thirteen events have radio observations from the Very Large Array, with eight detections and five non-detections. We find that the populations that have radio detections and radio non-detections are indistinct from one another with respect to their optically inferred explosion properties, and there are no statistically significant correlations present between the events’ radio luminosities and optically inferred explosion properties. This provides evidence that the explosion properties derived from optical data alone cannot give inferences about the radio properties of SNe Ic-BL and likely their relativistic jet formation mechanisms.