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The light curve model fitting of Large Magellanic Cloud Cepheids: MESA-RSP versus Stellingwerf’s code predictions
No full textContext. A major challenge in modeling classical Cepheids is the treatment of convection, particularly its complex interplay with pulsation. This inherently three-dimensional (3D) process is typically approximated in one-dimensional (1D) hydrocodes, using dimensionless turbulent convection (TC) free parameters. Calibrating these parameters is essential for reproducing key observational features, such as the light curve amplitudes, secondary bumps, and the red edge of the instability strip (IS).
Aims. In this work, we calibrate the TC parameters adopted from the publicly available Modules for Experiments in Stellar Astrophysics-Radial Stellar Pulsations (MESA-RS
Optimal multi-round portfolio crowdfunding financing and capital structure
No full textThis study investigates the start-up firm’s optimal decision in multi-round equity and debt portfolio crowdfunding financing and the design of risk-sharing mechanism. A crowdfunding platform serves as an intermediary between a start-up firm with limited initial capital and external investors seeking debt and equity investments. When the funding target is not met, the crowdfunding platform provides loans to bridge the start-up firm’s capital gap, which also gives chance to adjust its capital structure. Firstly, a decision-making model is established to derive optimal financing strategies for a startup firm and a crowdfunding platform, while also derived the financing ratio between equity and debt crowdfunding channels. A numerical analysis further examines how key parameterssuch as fundraising rate and loan interest rateaffect the startup’s capital structure. More importantly, a novel debt-to-equity swap arrangement (DTE) is proposed for sharing debt risk between the start-up firm and the platform. The findings reveal that startup firms primarily rely on equity crowdfunding when the fundraising rate is moderate, while the low fundraising rate leads to a single equity crowdfunding approach. Similarly, the high loan interest rate drive startup firms to favor equity crowdfunding, whereas low rates may prompt platform to discontinue loans, leaving startup firms to rely solely on equity financing. Additionally, the DTE facilitates coordination among parties requires balanced adjustments from platforms (moderate commission rates), startup firm (capital structure optimization), and investors (appropriate success rates) to ensure effective risk-sharing and profit distribution
Mn-doped Bi
No full textThe current research investigates the influence of manganese (Mn) doping on the structural, optical, and dielectric properties of Bi2-xMnxO3 thin films for optoelectronic applications. The prepared thin films with different Mn content (x = 0, 0.025, 0.05, 0.075, and 0.1) were synthesized, and their characteristics were thoroughly analyzed. Our findings demonstrate that increasing manganese content enhances light absorption by creating new electronic states, which is reflected in higher absorbance and lower transmittance values. The direct optical band gap decreases with higher Mn incorporation (from 3.60 eV for x = 0–3.29 eV for x = 0.1), suggesting a tunable electronic structure. Furthermore, the Urbach energy increases with Mn concentration from 1.23 eV for x = 0–3.33 eV for x = 0.1, indicating enhanced structural disorder and broadening of the band tail, which can benefit photovoltaic applications. Analysis of refractive index, extinction coefficient, and dielectric parameters (ε1, ε2, Tanδ) demonstrates improved optical density, dielectric polarization, and reduced dielectric losses with Mn doping. These results establish clear correlations between Mn concentration and the resulting physical properties, providing crucial insights for optimizing Bi2O3-based materials for high-performance optoelectronic applications
HST pre-imaging of a free-floating planet candidate microlensing event
No full textHigh-cadence microlensing observations uncovered a population of very short-timescale microlensing events, which are believed to be caused by the population of free-floating planets (FFPs) roaming the Milky Way. Unfortunately, the light curves of such events are indistinguishable from those caused by wide-orbit planets. To properly differentiate both cases, one needs high-resolution observations that would allow one to resolve a putative luminous companion to the lens long before or after the event. Usually, the baseline between the event and high-resolution observations needs to be quite long (∼10 yr), hindering potential follow-up efforts. However, there is a chance to use archival data if they exist. Here, we present an analysis of the microlensing event OGLE-2023-BLG-0524, the site of which was captured in 1997 with the Hubble Space Telescope (HST). Hence, we achieve a record-breaking baseline length of 25 years. A very short duration of the event (tE = 0.346 ± 0.008 d) indicates an FFP as the explanation. Based on the finite-source effects in the light curve, we measure an angular Einstein radius value of θE = 4.78 ± 0.23 μas, suggesting a super-Earth in the Galactic disk or a sub-Saturn-mass planet in the Galactic bulge. We have not detected any potential companion to the lens with the HST data, which is consistent with the FFP origin of the event. Though we detect no potential companion to the lens in the HST imaging, we find that the HST imaging is insufficient to constrain beyond 25-48% of potential companions (depending on whether or not the occurrence rate of wide-orbit planets is correlated with the host mass); hence, we are unable to confidently confirm this event as an FFP. Despite this, our results show that archival high-resolution images should be available for many microlensing events, providing a potential new avenue to confirm FFP candidates in future observations
X-ray, optical, and radio follow-up of five thermally emitting isolated neutron star candidates
No full textWe report on follow-up observations with XMM-Newton, the FORS2 instrument at the ESO-VLT, and FAST, aiming to characterise the nature of five thermally emitting isolated neutron star (INS) candidates recently discovered from searches in the footprint of the Spectrum Roentgen Gamma (SRG)/eROSITA All-sky Survey. We find that the X-ray spectra are predominantly thermal and can be described by low-absorbed blackbody models with effective temperatures ranging from 50 to 210 eV. In two sources, the spectra also show narrow absorption features at 300–400 eV. Additional non-thermal emission components are not detected in any of the five candidates. The soft X-ray emission, the absence of optical counterparts in four sources, and the consequent large X-ray-to-optical flux ratios > 3000 − 5400 confirm their INS nature. For the remaining source, eRASSU J144516.0–37442
A decade of solar high-fidelity spectroscopy and precise radial velocities from HARPS-N
No full textContext. The HARPS-N solar telescope has been observing the Sun every possible day since the summer of 2015. We have recently released 10 years of these data, which are available online.
Aims. The goal of this paper is to present the different optimisations made to the ESPRESSO data reduction software used to extract the published HARPS-N solar spectra, describe the data curation, and perform some analyses that demonstrate the extreme radial velocity (RV) precision of those data.
Methods. By analysing all of the HARPS-N wavelength solutions over 13 years, we brought to light instrumental systematics at the 1 m s−1 level. We mitigated those systematics by curating the thorium line list used to derive the wavelength solution and applying a correction to the drift of thorium lines induced by the aging of thorium-argon hollow cathode lamps. After optimisation, we demonstrated a peak-to-peak precision on the HARPS-N wavelength solution better than 0.75 m s−1 over 13 years. We then carefully curated the decade of HARPS-N re-reduced solar observations by rejecting 30% of the data affected either by clouds, bad atmospheric conditions, or well-understood instrumental systematics. Finally, we corrected the curated data for spurious sub-meter-per-second RV effects caused by erroneous instrumental drift measurements and by changes in the spectral blaze function over time.
Results. After curation and correction, a total of 109,466 HARPS-N solar spectra and respective RVs over a decade were made available. The median photon-noise precision of the RV data is 0.28 m s−1, and on daily timescales, the median RV rms is 0.49 m s−1, which is similar to the level imposed by stellar granulation signals. On 10 year timescales, the large RV rms of 2.95 m s−1 results from the RV signature of the Sun’s magnetic cycle. Through modelling of this long-term effect using the Bremen composite magnesium II activity index, we demonstrate a long-term RV precision of 0.41 m s−1. We also analysed contemporaneous HARPS-N and NEID solar RVs and found the data from both instruments to be of similar quality and precision. However, an analysis of the RV difference between these two RV datasets over the three available years gave a surprisingly large RV rms of 1.3 m s−1. This variation is dominated by an unexplained trend that could be caused by a different sensitivity to stellar activity of the two datasets. Once this trend was modelled, the overall RV rms for three years reached 0.79 m s−1, and the RV rms during the low-activity phase decreased to 0.6 m s−1, compatible with what is expected from supergranulation.
Conclusions. This decade of high-cadence HARPS-N solar observations with short- and long-term precision below one m s−1 represents a crucial dataset in the pursuit of further understanding the stellar activity signals in solar-type stars and advancing other science cases requiring such extreme precision
Emission-line and continuum reverberation mapping of the NLS1 galaxy WPVS 48
No full textContext. WPVS 48 is a nearby narrow-line Seyfert 1 galaxy without previous analysis of the broad-line region (BLR) by means of optical spectroscopic reverberation mapping.
Aims. By studying the continuum and emission line variability of WPVS 48, our aim was to infer the BLR size as well as the mass of the central supermassive black hole (SMBH).
Methods. We analysed data from a dedicated optical spectroscopic reverberation mapping campaign of WPVS 48 taken with the 10 m Southern African Large Telescope (SALT) at 24 epochs over a period of seven months between December 2013 and June 2014.
Results. WPVS 48 shows variability throughout the campaign. We find a stratified BLR, where the variability amplitude of the integrated emission lines decreases with distance to the ionising continuum source. Specifically, the variable emission of Hα, Hβ, Hγ, and He
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No full textThe recent discovery of five massive stellar clusters at z = 9.625 in the Cosmic Gems galaxy has raised the question about the formation mechanism of star clusters in the first 500 Myr after the Big Bang. We inferred the total stellar mass in clusters by normalizing and integrating the stellar cluster mass function (SCMF, dn(M)/dM = n0Mβ), assuming three different slopes (β = −1.5, −2.0, and −2.5) and different lower-mass limits between 102 and 105 M⊙. We compared the total integrated cluster stellar mass to the stellar mass inferred from the counter image of the Cosmic Gems, which provides the best modestly magnified (μ = 1.84 ± 0.05) representation of the entire galaxy. The delensed stellar mass of the Cosmic Gems galaxy was estimated as M⊙, with an effective radius of parsecs and a stellar surface mass density of M⊙ pc−2. Accounting for normalization uncertainties – including different lensing magnification scenarios for the arc – a modified SCMF, combined with a significantly high star cluster formation efficiency (approaching 100%), appears to be a necessary condition to explain the relatively short formation timescale of both the star clusters and the counter image, without exceeding the galaxy’s stellar mass. By extrapolating the physical properties at the peak of the burst, we found that in its recent past (≲30 Myr) the Cosmic Gems galaxy likely experienced a specific star formation rate exceeding 25 Gyr−1 and luminosity approaching the “blue monster” regime (MUV < −20). Our study provides insights into the extreme clustered nature of star formation in early galaxies and sheds light on the formation of bound star clusters that might survive to z = 0 as globular clusters older than 13 Gyr
Shock-type inference of L1157 B2 using methanol desorption
No full textContext. Shock types of low-velocity molecular outflows are not always well constrained. Astrochemical comparisons are often made between low-velocity and high-velocity outflows, but without considering the question of the shock type.
Aims. We investigated molecular abundances of post-shock regions to determine whether strong differences between non-irradiated C-type and J-type shocks can be highlighted. One of the main application goals is to diagnose the shock type of the protostellar object L1157 B2 through the use of molecular tracers.
Methods. We simulated grid sets of shock models with the Paris-Durham Shock code with velocities ranging from 5 to 19 km/s and low densities from 102 to 105 cm−3. We computed the desorption percentage of methanol in these simulations and estimated it at higher velocities. We compared our results to observational measurements of L1157 B2 and with a benchmark of four already identified shocks.
Results. L1157 B2 has been diagnosed as a non-irradiated C-type shock, and the method showed a good applicability through the benchmark. Methanol formed in the icy mantle of grains can serve to trace the differences between shock types, at least in non-irradiated conditions. A requirement for the applicability of a species as a shock-type tracer is that it does not undergo significant enhancement or destruction, but is mainly impacted by desorption processes under shocked conditions.
Conclusions. The desorption percentage of methanol is a good criterion in characterizing the shock type of L1157 B2 and should be investigated as a general method to diagnose the shock type in non-irradiated regions. We identify L1157 B2 as a non-irradiated C-type shock with velocities and densities fitting with previous studies
Chemodynamic evidence of pristine gas accretion in the void galaxy VGS 12
No full textContext. Accretion of metal-poor gas is expected to be an important channel of gas replenishment in galaxy evolution studies. However, observational evidence of this process is still relatively scarce.
Aims. The unusual polar disk galaxy VGS 12 was found in the Void Galaxy Survey. It appears to be isolated and resides in the cosmological wall between two large voids. The suggested formation scenario for this peculiar system is accretion of metal-poor gas from the void interior. To confirm or refute the accretion scenario, information on the chemical properties of VGS 12 is crucial and provides novel insights into gas accretion mechanisms when combined with kinematic constraints on the polar material.
Methods. We present for the first time the data on the gas-phase chemical abundance of VGS 12 obtained with the Russian 6m telescope BTA. We complement our analysis with HI data obtained with VLA and the data on the kinematics of the ionized gas.
Results. VGS 12 appears to be a strong outlier from the “metallicity–luminosity” relation, with gas oxygen abundance ∼0.7 dex lower than expected for its luminosity. The nitrogen abundance, on the other hand, is higher than what is typically observed in galaxies with similar metallicity, but is consistent with the metallicity expected given its luminosity. Such behavior is what is expected in the case of metal-poor gas accretion. The H