Effective Temperature Research Articles

Magnetic-guided nanocarriers for ionizing/non-ionizing radiation synergistic treatment against triple-negative breast cancer

BackgroundTriple-negative breast cancer (TNBC) is a subtype of breast cancer with the worst prognosis. Radiotherapy (RT) is one of the core modalities for the disease; however, the ionizing radiation of RT has severe side effects. The consistent development direction of RT is to achieve better therapeutic effect with lower radiation dose. Studies have demonstrated that synergistic effects can be achieved by combining RT with non-ionizing radiation therapies such as light and magnetic therapy, thereby achieving the goal of dose reduction and efficacy enhancement.MethodsIn this study, we applied FeCo NPs with magneto thermal function and phototherapeutic agent IR-780 to construct an ionizing and non-ionizing radiation synergistic nanoparticle (INS NPs). INS NPs are first subjected to morphology, size, colloidal stability, loading capacity, and photothermal conversion tests. Subsequently, the cell inhibitory and cellular internalization were evaluated using cell lines in vitro. Following comprehensive assessment of the NPs’ in vivo biocompatibility, tumor-bearing mouse model was established to evaluate their distribution, targeted delivery, and anti-tumor effects in vivo.ResultsINS NPs have a saturation magnetization exceeding 72 emu/g, a hydrodynamic particle size of approximately 40 nm, a negatively charged surface, and good colloidal stability and encapsulation properties. INS NPs maintain the spectral characteristics of IR-780 at 808 nm. Under laser irradiation, the maximum temperature was 92 °C, INS NPs also achieved the effective heat temperature in vivo. Both in vivo and in vitro tests have proven that INS NPs have good biocompatibility. INS NPs remained effective for more than a week after one injection in vivo, and can also be guided and accumulated in tumors through permanent magnets. Later, the results exhibited that under low-dose RT and laser irradiation, the combined intervention group showed significant synergetic effects, and the ROS production rate was much higher than that of the RT and phototherapy-treated groups. In the mice model, 60% of the tumors were completely eradicated.ConclusionsINS NPs effectively overcome many shortcomings of RT for TNBC and provide experimental basis for the development of novel clinical treatment methods for TNBC.

Discovery of the Remarkably Red L/T Transition Object VHS J183135.58-551355.9

We present the discovery of VHS J183135.58−551355.9 (hereafter VHS J1831−5513), an L/T transition dwarf identified as a result of its unusually red near-infrared colors (J − K S = 3.633 ± 0.277 mag; J − W2 = 6.249 ± 0.245 mag) from the VISTA Hemisphere Survey and CatWISE2020 surveys. We obtain low-resolution near-infrared spectroscopy of VHS J1831−5513 using the Magellan Folded port InfraRed Echellette spectrograph to confirm its extremely red nature and assess features sensitive to surface gravity (i.e., youth). Its near-infrared spectrum shows multiple CH4 absorption features, indicating an exceptionally low effective temperature for its spectral type. Based on proper-motion measurements from CatWISE2020 and a photometric distance derived from its K s -band magnitude, we find that VHS J1831−5513 is a likely (∼85% probability) kinematic member of the β Pictoris moving group. Future radial velocity and trigonometric parallax measurements will clarify such membership. Follow-up mid-infrared or higher-resolution near-infrared spectroscopy of this object will allow for further investigation as to the cause(s) of its redness, such as youth, clouds, and viewing geometry.

Astrophysical calibration of the oscillator strengths of YJ-band absorption lines in classical Cepheids

ABSTRACT Newly-developed spectrographs with increased resolving powers, particularly those covering the near-IR range, allow the characterization of more and more absorption lines in stellar spectra. This includes the identification and confirmation of absorption lines and the calibration of oscillator strengths. In this study, we provide empirical values of ${{\rm log} gf}$ based on the abundances of classical Cepheids obtained with optical spectra to establish the consistency between optical and infrared abundance results. Using time series spectra of classical Cepheids obtained with WINERED spectrograph (0.97–1.35 $\mu$m, R$\sim$ 28000), we demonstrate that we can determine the stellar parameters of the observed Cepheids, including effective temperature (${T_\mathrm{eff}}$), surface gravity (${{\rm log} g}$), microturbulence ($\xi$), and metallicity (${\rm {[{\mathrm{ M}}/\mathrm{ H}]}}$). With the newly calibrated relations of line-depth ratios, we can achieve accuracy and precision comparable to optical studies, with uncertainties of $\sim$90 K and 0.108 dex for ${T_\mathrm{eff}}$, and ${{\rm log} g}$, respectively. Finally, we created a new atlas of absorption lines, featuring precise abundance measurements of various elements found in the atmosphere of Cepheids, including neutron-capture elements whose ${{\rm log} gf}$ values have been astrophysically calibrated.

An improved analytical model of effective thermal conductivity for hydrate-bearing sediments during elastic-plastic deformation and local thermal stimulation

As one of the crucial thermal properties controlling the dissociation of natural gas hydrate (NGH), effective thermal conductivity (ETC) should be precisely determined to improve the efficiency of NGH exploitation. But so far, most existing analytical ETC models of hydrate-bearing sediments could not accurately characterize the evolution of ETC. In this paper, an improved analytical model is derived for quantitatively revealing physical relations between ETC and various influencing factors during elastic-plastic deformation and local thermal stimulation processes, including hydrate saturation change, complex pore structures evolution, and hydrate occurrence patterns transition. The effectiveness of the proposed model is validated against available experimental data and compared with other existing models, then effects of various critical parameters on ETC are investigated. Results show that the porosity of hydrate-bearing sediments is accurately predicted during both loading and unloading processes, and the calculated ETC values under various conditions (effective stress, hydrate saturation, and temperature) are satisfactory with the test data. Contributions of elastic deformation and plastic deformation to ETC increments are quantitatively obtained. It is noteworthy that this proposed model is significant to reveal the evolution mechanisms of ETC, helping to accurately predict gas production and offer better plans for efficient NGH exploitations.

Temperature optimization model to inhibit zero-order kinetic reactions

Abstract Originally, the Arrhenius parameters were used to estimate the rate of chemical reactions. This article aims to develop the optimal temperature to inhibit specific zero-order kinetic reactions. The model extends the use of the Arrhenius equation and heat capacity modeling to derive the optimal temperature solution. Specifically, the Arrhenius equation, which connects temperature to reaction rates, and the heat equation are formulated to create a comprehensive heat accumulation model. Analytical modeling is utilized through a derivative process to provide optimization. According to a case study of carotene oxidation, the derivative solution proposes −1.73 °C and can extend the reaction time by 206,160.29 days compared to a solution with no temperature change. The derivative solution also offers higher advantages in practical application than setting the lowest temperature limit due to the high initial energy requirement. The temperature derivative solution exhibits a global optimum property because of its high heat accumulation and slower kinetic reactions. These slower kinetic reactions can prevent reactant substances from deteriorating, making them valuable for maintaining a chemical’s shelf life. The temperature solutions offer valuable insights for devising an effective temperature strategy to inhibit specific chemical processes and verifying the relationship between temperature and heat accumulation with curvature.

A search for Galactic post-asymptotic giant branch stars in Gaia DR3

When low- and intermediate-mass stars leave the asymptotic giant branch (AGB) phase, and before they reach the planetary nebula stage, they enter a very brief and rather puzzling stellar evolutionary stage called post-AGB stage. The post-AGB phase lasts very briefly, about a few thousand years at most. The number of objects that are confirmed in this phase therefore is really small, and our understanding of this elusive stellar evolutionary stage is accordingly very limited. We provide a reliable catalogue of Galactic post-AGB stars together with their physical and evolutionary properties obtained through Gaia DR3 astrometry and photometry. As an added product, we provide information for a sample of other types of stellar objects, whose observational properties mimic those of post-AGB stars. Post-AGB stars are characterised by their infrared excesses and high luminosities. The publication of precise parallaxes in Gaia DR3 made it possible to calculate accurate distances and to revise the derivation of luminosities for post-AGB candidates, so that objects outside the expected luminosity range can be discarded. We started by identifying post-AGB stars or possible candidates from the bibliography, and we then searched for their Gaia DR3 counterpart sources. Using the available photometry, interstellar extinction, spectroscopically derived temperatures or spectral types and parallax-derived distances from the literature, we fitted their spectral energy distributions and estimated their luminosities and circumstellar extinctions. By a comparison to models, the luminosity values allowed us to determine which objects are likely post-AGB stars from other target types. Their position in the Hertzsprung-Russell diagram allows a direct comparison with updated post-AGB evolutionary tracks and an estimation of their masses and evolutionary ages. We obtained a sample of 69 reliable post-AGB candidates that meet our classification criteria, which provide their coordinates, distances, effective temperature, interstellar and circumstellar extinction, luminosity, mass, and evolutionary age. In addition, we provide similar data for other stellar objects in our initial compilation, such as supergiant stars and young stellar objects. Our identifications and parameters are compared with others found in the recent literature for the subject. We selected the data with the best precision in parallax and distance to obtain more accurate luminosities, which allowed us to confidently classify the objects of the sample in different stellar phases. In turn, this allowed us to provide a small but reliable sample of post-AGB objects. The derived mean evolutionary time and average mass values agree with theoretical expectations and with the mean mass value obtained in a previous work for the subsequent evolutionary stage, the planetary nebula stage.

Updated Spectral Characteristics for the Ultracool Dwarf TRAPPIST-1

A comprehensive infrared spectroscopic study of star TRAPPIST-1 is a crucial step toward the detailed examination of its planets. While the presence of Earth’s atmosphere has limited the spectral extent of such a study up to now, the Near Infrared Imager and Slitless Spectrograph (NIRISS) and the Near Infrared Spectrograph instruments aboard the James Webb Space Telescope (JWST) can now yield the 0.6–5 μm spectral energy distribution (SED) of the star. Here we translate TRAPPIST-1's SED into tight constraints on its luminosity (L bol = 0.000566 ± 0.000022 L ⊙), effective temperature (T eff = 2569 ± 28 K), and metallicity ([Fe/H] = 0.052 ± 0.073) and investigate the behavior of its gravity-sensitive indices. Through band-by-band comparisons of the NIRISS and ground-based spectra, TRAPPIST-1 exhibits a blend of both field source and intermediate-gravity spectral characteristics, suggesting that the star is likely a field-age source with spectral features reminiscent of young objects. We also employ photospheric modeling incorporating theoretical and JWST spectra to constrain stellar surface heterogeneities, finding that the limited fidelity of current stellar spectral models precludes definitive constraints on the physical parameters of the distinct spectral components giving rise to TRAPPIST-1's photospheric heterogeneity and variability. In addition, we find intermodel differences in the inferences of properties (e.g., the effective temperature) over one order of magnitude larger than the instrument-driven uncertainties (∼100 K vs. ∼4 K), pointing toward a model-driven accuracy wall. Our findings call for a new generation of stellar models to support the optimal mining of JWST data and further constraining stellar—and ultimately planetary—properties.

On the effective vibrational temperature of the source using (2)3∏ - X3∏ system of GeC molecule

In this work, the experimental potential energy curves for (2)3Π and X3Π electronic states of GeC molecule have been constructed by using Rydberg-Klein-Rees (RKR) method. The radiative transition parameters viz., Franck-Condon (FC) factor, r-centroid, electronic transition moment, band strength, relative band strength, Einstein coefficients, radiative lifetime and oscillator strength for the (2)3Π−X3Π system of GeC molecule have been estimated for the experimentally observed vibrational levels from Rydberg-Klein-Rees (RKR) potential and the estimated values are tabulated. The estimated effective vibrational temperature found as 5628 K for the (2)3Π−X3Π system of GeC molecule. The radiative transition parameters and effective vibrational temperature are evident that the possible presence of GeC molecule in solar and sunspots atmosphere. Further, these parameters are employed in rationalizations of astrochemical and astrophysical observations.

Distance Estimate Method for Asymptotic Giant Branch Stars Using Infrared Spectral Energy Distributions

We present a method to estimate distances to asymptotic giant branch (AGB) stars in the Galaxy, using spectral energy distributions (SEDs) in the near- and mid-infrared. By assuming that a given set of source properties (initial mass, stellar temperature, composition, and evolutionary stage) will provide a typical SED shape and brightness, sources are color matched to a distance-calibrated template and thereafter scaled to extract the distance. The method is tested by comparing the distances obtained to those estimated from very long baseline interferometry or Gaia parallax measurements, yielding a strong correlation in both cases. Additional templates are formed by constructing a source sample likely to be close to the Galactic center, and thus with a common, typical distance for calibration of the templates. These first results provide statistical distance estimates to a set of almost 15,000 Milky Way AGB stars belonging to the Bulge Asymmetries and Dynamical Evolution (BAaDE) survey, with typical distance errors of ±35%. With these statistical distances, a map of the intermediate-age population of stars traced by AGBs is formed, and a clear bar structure can be discerned, consistent with the previously reported inclination angle of 30° to the GC–Sun direction vector. These results motivate deeper studies of the AGB population to tease out the intermediate-age stellar distribution throughout the Galaxy, as well as determining statistical properties of the AGB population luminosity and mass-loss-rate distributions.

Absolute dimensions of solar-type eclipsing binaries

Context. The binary star NY Hya is a bright, detached, double-lined eclipsing system with an orbital period of just under five days with two components each nearly identical to the Sun and located in the solar neighbourhood. Aims. The objective of this study is to test and confront various stellar evolution models for solar-type stars based on accurate measurements of stellar mass and radius. Methods. We present new ground-based spectroscopic and photometric as well as high-precision space-based photometric and astrometric data from which we derive orbital as well as physical properties of the components via the method of least-squares minimisation based on a standard binary model valid for two detached components. Classic statistical techniques were invoked to test the significance of model parameters. Additional empirical evidence was compiled from the public domain; the derived system properties were compared with archival broad-band photometry data enabling a measurement of the system’s spectral energy distribution that allowed an independent estimate of stellar properties. We also utilised semi-empirical calibration methods to derive atmospheric properties from Strömgren photometry and related colour indices. Results. We measured (percentages are fractional uncertainties) masses, radii, and effective temperatures of the two stars in NY Hya and found them to be MA = 1.1605 ± 0.0090 M⊙ (0.78%), RA = 1.407 ± 0.015 R⊙ (1.1%), Teff, A = 5595 ± 61 K (1.09%), MB = 1.1678 ± 0.0096 M⊙ (0.82%), RB = 1.406 ± 0.017 R⊙ (1.2%), and Teff, B = 5607 ± 61 K (1.09%). The atmospheric properties from Strömgren photometry agree well with spectroscopic results. No evidence was found for nearby companions from high-resolution imaging. A detailed analysis of space-based data revealed a small but significant eccentricity (e cos ω) of the orbit. The spectroscopic and frequency analysis on photometric time series data reveal evidence of clear photospheric activity on both components likely in the form of star spots caused by magnetic activity. Conclusions. We confronted the observed physical properties with classic and magnetic stellar evolution models. Classic models yielded both young pre-main-sequence and old main-sequence turn-off solutions with the two components at super-solar metallicities, in disagreement with observations. Based on chromospheric activity and X-ray observations, we invoke magnetic models. While magnetic fields are likely to play an important role, we still encounter problems in explaining adequately the observed properties. To reconcile the observed tensions we also considered the effects of star spots known to mimic magnetic inhibition of convection. Encouraging results were obtained, although unrealistically large spots were required on each component. Overall we conclude that NY Hya proves to be complex in nature, and requires additional follow-up work aiming at a more accurate determination of stellar effective temperature and metallicity.

Constraints from Parallaxes and Average Period Spacings in the Asteroseismic Study of Eight Hydrogen-atmosphere Pulsating White Dwarfs

With space missions such as Kepler, TESS, and Gaia, we have a wealth of data on pulsating white dwarfs that can be leveraged in white dwarf asteroseismology. We address the question of the proportion of white dwarfs with thin hydrogen layers versus those with thick hydrogen layers. We also provide a mass–radius relation for carbon–oxygen-core, hydrogen-atmosphere white dwarfs. Such a relationship can be used in conjunction with magnitudes and distance measurements to constrain the mass and effective temperature of the white dwarfs. We select nine hydrogen-atmosphere pulsating white dwarfs for their rich pulsation spectra. From such pulsation spectra, we can derive the asymptotic period spacing, which in turn allows us to determine the thickness of the hydrogen and helium envelope of the models, without having to perform period-by-period fitting. We find that the majority of the white dwarfs have thicker hydrogen layers and we determine an upper limit of M r = 1–10−2.2 for the location of the base of the helium layer, in accordance with stellar evolution models. We confirm a finding from earlier studies that used a mass–radius relation and Gaia data to determine the effective temperatures of white dwarfs. The Gaia data systematically point to white dwarfs of lower effective temperature than indicated by the spectroscopy. Our results also support the hypothesis that white dwarfs with thicker hydrogen layers are more common than those with thinner layers.

Stellar Characterization and a Chromospheric Activity Analysis of a K2 Sample of Planet-hosting Stars

Effective temperatures, surface gravities, and iron abundances were derived for 109 stars observed by the K2 mission using equivalent width measurements of Fe i and Fe ii lines. Calculations were carried out in local thermodynamic equilibrium using Kurucz model atmospheres. Stellar masses and radii were derived by combining the stellar parameters with Gaia Data Release 3 parallaxes, V magnitudes, and isochrones. The derived stellar and planetary radii have a median internal precision of 1.8% and 2.3%, respectively. The radius gap near R planet ∼ 1.9 R ⊕ was detected in this K2 sample. Chromospheric activity was measured from the Ca ii H and K lines using the values of logRHK′ , which were investigated as a function of stellar rotational period (P rot), and we found that chromospheric activity decreases with increasing P rot, although there is a large scatter in logRHK′ (∼0.5) for a given P rot. The activity levels in this sample reveal a paucity of F and G dwarfs with intermediate activity levels (the Vaughan–Preston gap). The effect that stellar activity might have on the derivation of stellar parameters was investigated by including magnetically sensitive Fe i lines in the analysis and we find no significant differences between parameters with and without magnetically sensitive lines, although the more active stars ( logRHK′>−5.0 ) exhibit a larger scatter in the differences in T eff and [Fe/H].

Three short-period Earth-sized planets around M dwarfs discovered by TESS: TOI-5720 b, TOI-6008 b, and TOI-6086 b

One of the main goals of the NASA Transiting Exoplanet Survey Satellite (TESS) mission is the discovery of Earth-like planets around nearby M-dwarf stars. We present the discovery and validation of three new short-period Earth-sized planets orbiting nearby M dwarfs: TOI-5720 b, TOI-6008 b, and TOI-6086 b. We combined TESS data, ground-based multicolor light curves, ground-based optical and near-infrared spectroscopy, and Subaru/IRD radial velocity data to validate the planetary candidates and constrain the physical parameters of the systems. In addition, we used archival images, high-resolution imaging, and statistical validation techniques to support the planetary validation. TOI-5720 b is an Earth-sized planet with a radius of Rp = 1.09 ± 0.07 R⊕. It orbits a nearby (36 pc) M 2.5 host with an orbital period of P = 1.4344555 ± 0.0000036 days. It has an equilibrium temperature of Teq = 708 ± 19 K (assuming a null albedo) and an incident flux of Sp = 41.7 ± 4.5 S⊕. TOI-6008 b is a short-period planet of P = 0.8574347 ± 0.0000424 day. It has a radius of Rp = 1.03 ± 0.05 R⊕, an equilibrium temperature of Teq = 707 ± 19 K, and an incident flux of Sp = 41.5 ± 4.5 S⊕. The host star (TOI-6008) is a nearby (23 pc) M 5 with an effective temperature of Teff = 3075 ± 75 K. Based on the radial velocity measurements collected with Subaru/IRD, we set a 3σ upper limit of Mp < 4 M⊕, thus ruling out a star or brown dwarf as the transiting companion. TOI-6086 b orbits its nearby (32 pc) M 3 host star (Teff = 3200 ± 75 K) every 1.3888725 ± 0.0000827 days and has a radius of Rp = 1.18 ± 0.07 R⊕, an equilibrium temperature of Teq = 634 ± 16 K, and an incident flux of Sp = 26.8 ± 2.7 S⊕. Additional high-precision radial velocity measurements are needed to derive the planetary masses and bulk densities and to search for additional planets in the systems. Moreover, short-period Earth-sized planets orbiting around nearby M dwarfs are suitable targets for an atmospheric characterization with the James Webb Space Telescope through transmission and emission spectroscopy and phase-curve photometry.

The IACOB project

Context. Blue supergiants (BSGs) are key objects for understanding the evolution of massive stars, which play a crucial role in the evolution of galaxies. However, discrepancies between theoretical predictions and empirical observations have opened up important questions yet to be answered. Studying statistically significant and unbiased samples of these objects can help to improve the situation. Aims. We perform a homogeneous and comprehensive quantitative spectroscopic analysis of a large sample of Galactic luminous blue stars (a majority of which are BSGs) from the IACOB spectroscopic database, providing crucial parameters to refine and improve theoretical evolutionary models. Methods. We derived the projected rotational velocity (υ sin i) and macroturbulent broadening (υmac) using IACOB-BROAD, which combines Fourier transform and line-profile fitting techniques. We compared high-quality optical spectra with state-of-the-art simulations of massive star atmospheres computed with the FASTWIND code. This comparison allowed us to derive effective temperatures (Teff), surface gravities (log 𝑔), microturbulences (ξ), surface abundances of silicon and helium, and to assess the relevance of stellar winds through a wind-strength parameter (log Q). Results. We provide estimates and associated uncertainties of the above-mentioned quantities for the largest sample of Galactic luminous O9 to B5 stars spectroscopically analyzed to date, comprising 527 targets. We find a clear drop in the relative number of stars at Teff ≈ 21 kK, coinciding with a scarcity of fast rotating stars below that temperature. We speculate that this feature (roughly corresponding to B2 spectral type) might be roughly delineating the location of the empirical terminal-age main sequence in the mass range between 15 and 85 M⊙. By investigating the main characteristics of the υ sin i distribution of O stars and BSGs as a function of Teff, we propose that an efficient mechanism transporting angular momentum from the stellar core to the surface might be operating along the main sequence in the high-mass domain. We find correlations between ξ,υmac and the spectroscopic luminosity 𝓛 (defined as Teff4 / g). We also find that no more than 20% of the stars in our sample have atmospheres clearly enriched in helium, and suggest that the origin of this specific subsample might be in binary evolution. We do not find clear empirical evidence of an increase in the wind strength over the wind bi-stability region toward lower Teff.

Lithium, rotation and metallicity in the open cluster M35

Context. Lithium (Li) abundance is an age indicator for G, K, and M stellar types, as its abundance decreases over time for these spectral types. However, despite all of the observational efforts made over the past few decades, the role of rotation, stellar activity, and metallicity in the depletion of Li is still unclear. Aims. Our purpose is to investigate how Li depletion is affected by rotation and metallicity in G and K members of the roughly Pleiades-aged open cluster M35. Methods. We have collected an initial sample of 165 candidate members observed with the WIYN/Hydra spectrograph. In addition, we have taken advantage of three previous spectroscopic studies of Li in M35. As a result, we have collected a final sample of 396 stars observed with the same instrument, which we have classified as non-members, possible non-members, possible members, and probable members of the cluster. We have measured iron abundances, Li equivalent widths, and Li abundances for the 110 M35 members added to the existing sample by this study. Finally, rotation periods for cluster members have been obtained from the literature or derived from Zwicky Transient Facility light curves. Results. We have confirmed that fast G and K rotators are Li-rich in comparison with slow rotators of similar effective temperature. This trend, which is also seen in previous studies, is more evident when binaries are not taken into account. Furthermore, while we derived an average metallicity of [Fe/H] = −0.26 ± 0.09 from our spectra, the distribution of Li in M35 is similar to those observed for the Pleiades and M34 open clusters, which have solar metallicity and slightly different ages. In addition, we have shown that an empirical relationship proposed to remove the contribution of the Fe I line at 670.75 nm to the blended feature at 670.78 nm overestimates by 5–15 mÅ the contribution of this iron line for M35 members. Conclusions. M35 fast G and K rotators have depleted less Li than their slower counterparts. Furthermore, a 0.2−0.3 dex difference in metallicity appears to make little difference in the Li distributions of open clusters with ages between 100 and 250 Myr.

Using autoencoders and deep transfer learning to determine the stellar parameters of 286 CARMENES M dwarfs

Context. Deep learning (DL) techniques are a promising approach among the set of methods used in the ever-challenging determination of stellar parameters in M dwarfs. In this context, transfer learning could play an important role in mitigating uncertainties in the results due to the synthetic gap (i.e. difference in feature distributions between observed and synthetic data). Aims. We propose a feature-based deep transfer learning (DTL) approach based on autoencoders to determine stellar parameters from high-resolution spectra. Using this methodology, we provide new estimations for the effective temperature, surface gravity, metallicity, and projected rotational velocity for 286 M dwarfs observed by the CARMENES survey. Methods. Using autoencoder architectures, we projected synthetic PHOENIX-ACES spectra and observed CARMENES spectra onto a new feature space of lower dimensionality in which the differences between the two domains are reduced. We used this low-dimensional new feature space as input for a convolutional neural network to obtain the stellar parameter determinations. Results. We performed an extensive analysis of our estimated stellar parameters, ranging from 3050 to 4300 K, 4.7 to 5.1 dex, and −0.53 to 0.25 dex for Teff, log 𝑔, and [Fe/H], respectively. Our results are broadly consistent with those of recent studies using CARMENES data, with a systematic deviation in our Teff scale towards hotter values for estimations above 3750 K. Furthermore, our methodology mitigates the deviations in metallicity found in previous DL techniques due to the synthetic gap. Conclusions. We consolidated a DTL-based methodology to determine stellar parameters in M dwarfs from synthetic spectra, with no need for high-quality measurements involved in the knowledge transfer. These results suggest the great potential of DTL to mitigate the differences in feature distributions between the observations and the PHOENIX-ACES spectra.

Harnessing the power of temperature gradient-enhanced pyroelectricity: self-powered temperature/light detection in Ce-doped HfO2 ferroelectric films with downward spontaneous polarization

Ferroelectric materials are ideal for self-powered sensors in Internet of Things (IoT) and high-precision detection systems due to their excellent polarization properties. Compatibility with miniaturization, high-density systems, and complementary metal oxide semiconductor (CMOS) processes is crucial for their widespread adoption. HfO2-based ferroelectric films show potential in self-powered pyroelectric sensors as their thinness enables effective temperature and light detection. However, the disordered ferroelectric domain distribution limits their pyroelectric performance and hampers the development of highly integrated self-powered pyroelectric devices. This report investigates the temperature and light detection capabilities of Ce-doped HfO2 ferroelectric films, which exhibit as-grown spontaneous polarization in the downward direction, making them a promising option for self-powered pyroelectric sensors. The findings provide robust evidence that the introduction of a temperature gradient significantly enhances pyroelectricity. In addition, their applications in the detection of hot/cold wind and breathing have been proved. Notably, the 30 nm thick Ce-doped HfO2 ferroelectric film has a high pyroelectric coefficient of about 894.7 μC·m–2·K–1 and enables high-precision detection of changes in temperature of 0.1 K. This study highlights the potential application of HfO2-based ferroelectric films in self-powered sensors with temperature and light detection capabilities, making them a promising candidate for future IoT-based systems and high-precision detection systems.

Multiband Simultaneous Photometry of Type II SN 2023ixf with Mephisto and the Twin 50 cm Telescopes

SN 2023ixf, recently reported in the nearby galaxy M101 at a distance of 6.85 Mpc, was one of the closest and brightest core-collapse supernovae in the last decade. In this work, we present multiwavelength photometric observation of SN 2023ixf with the Multi-channel Photometric Survey Telescope (Mephisto) in the uvgr bands and with the twin 50 cm telescopes in the griz bands. We find that the bolometric luminosity reached the maximum value of 3 × 1043 erg s−1 at 3.9 days after the explosion and fully settled onto the radioactive tail at ∼90 days. The effective temperature decreased from 3.2 × 104 K at the first observation and approached a constant of ∼(3000–4000) K after the first 2 months. The evolution of the photospheric radius is consistent with a homologous expansion with a velocity of 8700 km s−1 in the first 2 months, and it shrunk subsequently. Based on the radioactive tail, the initial nickel mass is about M Ni ∼ 0.098 M ⊙. The explosion energy and the ejecta mass are estimated to be E ≃ (1.0–5.7) × 1051 erg and M ej ≃ (3.8–16) M ⊙, respectively. The peak bolometric luminosity is proposed to be contributed by the interaction between the ejecta and the circumstellar medium (CSM). We find a shocked CSM mass of M CSM ∼ 0.013 M ⊙, a CSM density of ρ CSM ∼ 2.5 × 10−13 g cm−3, and a mass-loss rate of the progenitor of Ṁ∼0.022M⊙yr−1 .

Discovery of a Dusty Yellow Supergiant Progenitor for the Type IIb SN 2017gkk

Type IIb supernovae are an important subclass of stripped-envelope supernovae (SNe), which show H lines only at early times. Their progenitors are believed to contain a low-mass H envelope before explosion. This work reports the discovery of a progenitor candidate in preexplosion Hubble Space Telescope images for the Type IIb SN 2017gkk. With detailed analysis of its spectral energy distribution and local environment, we suggest that the progenitor is most likely a yellow supergiant with significant circumstellar extinction and has an initial mass of about 16 M ⊙, effective temperature log(T eff/K) = 3.72 ± 0.08, and luminosity log(L/L ⊙) = 5.17 ± 0.04. This progenitor is not massive enough to strip envelope through stellar wind, and it supports an interacting binary progenitor channel and adds to the growing list of direct progenitor detections for Type IIb SNe. Future late-time observations will confirm whether this progenitor candidate has disappeared and reveal the putative binary companion that has survived the explosion.

Magnetic field enhanced critical current in Ge–Si nanowire Josephson junctions

Anomalous critical current enhancement was observed with increasing magnetic field in Josephson junctions based on Ge–Si core-shell nanowires. Despite the predicted topological properties of these nanowires, which could potentially lead to non-trivial superconducting order parameter symmetries, our investigation unveils a more generalized, non-topological explanation for the observed critical current enhancement in these devices. Our findings suggest that the enhancement arises from a thermalization process induced by the magnetic field, wherein in-gap quasiparticles are generated. These quasiparticles play a crucial role in enhancing the cooling of the device, thereby lowering the effective temperature and resulting in an increased critical current. Furthermore, we elucidate how this thermalization effect varies with device geometry and measurement configuration.