Thousands of sub-Neptunes have been discovered mainly through space-based surveys such as Kepler and TESS. Their bulk compositions and internal structures are thought to reflect their formation and evolutionary pathways, and atmospheric observations provide constraints on these processes. The near-infrared helium triplet is a potential tracer of extended, escaping H/He atmospheres. Recent models that include geometric effects suggest that planets orbiting nearby late M dwarfs may offer favorable conditions for detecting this signal. Nevertheless, helium has been reported for only three planets around M dwarfs to date. We conducted high-resolution transmission spectroscopy of three sub-Neptunes (TOI-2136b, TOI-654b, and LP 791-18c) and a super-Earth (TOI-1634b) orbiting M dwarfs with the InfraRed Doppler (IRD) spectrograph on the Subaru Telescope. We find no statistically significant helium absorption in any target; accordingly, we derive 95
Abstract We have carried out orbital inspections of hierarchical triple systems with masses $m_0=m_2=1$ and $m_1=0.1$, initially set under the influence of the $6:1$ mean motion resonance (MMR) and the von Zeipel–Kozai–Lidov (ZKL) mechanism, aiming at investigating the role of the ZKL mechanism on the instability of the system. The systems were found to be hierarchically unstable within $2\times 10^5$ UoT, while an analysis of nearby orbits indicates that the systems could have a shorter life-time, $6.5\times 10^4$ UoT. The bodies $m_1$ and $m_2$ repeatedly have a chance of coming closer than usual when the phases of three distinct quantities, accounting for the degree or possibility of an $(m_1,m_2)$-approach, match well. On the other hand, we did not find any coplanar and hierarchically stable orbits that could become unstable simply by replacing their initial inclination with a larger value.
Measurement of the expansion structure of ejecta in supernova remnants (SNRs) provides important information about their explosion mechanism. We combine Chandra proper-motion measurements with XRISM Doppler measurements to derive an approximate, region-averaged three-dimensional velocity map of the Fe-K-emitting ejecta in Cassiopeia A (Cas A), one of the youngest Galactic core-collapse SNRs. Proper motions were measured using the optical flow method. We find that the Fe-K-emitting ejecta expand predominantly outward, except in the western region, with projected velocities of up to 4580 km/s. The southeastern ejecta exhibit the highest three-dimensional velocity, reaching 5160+-320 km/s, based on the combined proper-motion and Doppler measurements. This velocity exceeds those measured for intermediate-mass elements (IMEs) such as Si and S, and the corresponding ejecta exhibit a relatively small line-of-sight velocity dispersion. These results are broadly consistent with the previously suggested inversion between the Fe-rich and IME-rich ejecta layers. The apparent inward motion or emergence of a new Fe-K emission component in the western region may reflect interaction with dense surrounding material, although the present data do not allow us to distinguish uniquely between these possibilities or to determine their physical origin.
Type IIb supernovae exhibit diverse progenitor properties, and radio observations offer a unique probe of their mass-loss histories shortly before the explosion. We present Japanese VLBI Network single-baseline monitoring of the nearby Type IIb SN 2024iss at 6.9 and 8.4 GHz, spanning approximately one year after its discovery. Our radio observations have detected its emission at 10 and 23 days after the explosion, with subsequent epochs yielding non-detections. Based on the peak radio luminosity and peak time, SN 2024iss exhibits radio properties highly comparable to those of compact-envelope events. Using a synchrotron self-absorption (SSA) modeling, we estimate a progenitor mass-loss rate of Ṁ≈ 2.5 × 10^-6M_⊙ yr^-1 for a compact progenitor wind velocity of 100 kms^-1. Furthermore, our SSA analysis yields a mean expansion velocity of V_ sh≈ 3.3 × 10^4 kms^-1, which exceeds the theoretical shock velocity derived from the self-similar solution by a factor of ∼ 2.4. Even for the conservative upper-bound peak time, the SSA-derived velocity remains larger than the theoretical expectation by a factor of ≳ 1.7. To explain this velocity excess, we propose the presence of a confined, dense circumstellar matter (CSM) surrounding the progenitor. The shock emergence from this confined CSM may have accelerated the forward shock, pointing to a highly complex and non-steady mass-loss history shortly before the explosion.
Abstract This paper introduces a novel method for deriving wavefront phase information using the knife-edge test, which can be used for extended objects such as the Sun. The formula presented in this paper shows that an observed image contains a partial derivative of the ground-layer phase errors. Experiments are conducted in which two field stops are separately set on the solar limb on the focal plane, and two pupil images through each field stop are simultaneously observed using two high-speed cameras. Some degree of correlation is demonstrated between the two image sets, and their values tend to increase with narrower separation between the two field stops. These results are consistent with those expected using the presented formula.
Clumpy-gas radiation hydrodynamics (CRHD) for inhomogeneous cloudlet-gas mixtures is reformulated from the microscopic viewpoint. Under an appropriate scattering phase function for back-scattering-dominated cloudlets, the radiative transfer equation for cloudlet-gas mixtures is first written down, and then, radiative moment and hydrodynamical equations are derived. In spite of the different approaches, the resultant basic equations are almost the same as those previously derived from the macroscopic viewpoint, if the anisotropic parameter in the microscopic method is replaced by the cloudlet optical depth in the macroscopic one. This replacement is physically reasonable since the cloudlet optical depth is the cause of the (back-scattering-dominated) anisotropic scattering of cloudlets. The previous macroscopic descriptions for CRHD are analytically exact for a sheet-like stratus and easy to handle, whereas the present microscopic descriptions are principled and suitable to treat the radiative transfer problem of cloudlet-gas mixtures.
We present a differentiable hydrodynamical framework for modeling barred gas flow in the Milky Way and constraining broad low-loss regions in bar-pattern-speed parameter space from Galactic longitude–velocity data. The method evolves a neutral-gas disk in a fixed barred potential, projects it into longitude–velocity (ℓ–v) space, and compares predicted and target maps using a cosine-distance loss applied to processed and masked maps. This emphasizes large-scale morphology rather than the absolute emission scale. Because the forward model is differentiable, gradients with respect to the bar pattern speed can be computed and used for direct optimization in observable space. We validate the method with self-consistency hydrodynamical mocks and with an independent mock generated by a different solver with more realistic interstellar-medium physics. These tests recover or identify low-loss regions near the input pattern speed, showing that the method captures coherent bar-driven structures in ℓ–v space. We then apply the framework to the observed CO ℓ–v structure of the inner Milky Way. The data yield broad low-loss regions rather than a unique best-fitting value. These regions include moderate pattern speeds, |Ω_ b|∼30–40 km s^-1 kpc^-1, consistent with current stellar-dynamical constraints, although their location depends on the gas response time and viewing angle. This first application demonstrates the feasibility of differentiable hydrodynamical modeling of Galactic gas as an independent kinematic test of barred Milky Way models and as a step toward multi-parameter forward modeling in position–position–velocity space.
Be/X-ray binaries (BeXRBs) constitute a major subclass of high-mass X-ray binaries. They show intermittent X-ray activity with L_X > 10^36 erg s^-1, while remaining quiescent most of the time with L_X < 10^34 erg s^-1. BeXRBs generally have eccentric orbits as a result of supernova kicks when neutron stars were born. In these systems, the same kicks are also likely to make the binary orbital axis misaligned with the spin axis of the Be star. In such systems, when the neutron star captures gas from the equatorial disk of the Be star, the resulting accretion disk is in general tilted to both the Be disk plane and to the binary orbital plane. This raises an interesting possibility that in misaligned BeXRBs, the polar wind of the Be star collides with the accretion disk and significantly affects its structure by the large ram pressure. In this paper, we study the effects of the stellar wind on the accretion dynamics in misaligned BeXRBs. Using analytical wind and disk models, we first compare the wind's ram pressure with the gas pressures of the accretion flow to derive a condition for the stellar wind to strongly suppress accretion, and then apply the condition to a sample of BeXRBs whose relevant parameters are well determined or constrained. We find that wind-driven inhibition is a plausible mechanism for suppressing accretion in systems with slowly rotating neutron stars in wide orbits, where the classical propeller mechanism is expected to be inefficient. The effect is particularly important if the accretion flow is hot and low-density, or after the accretion rate has declined from the outburst level.
With the continuous development of research on optical-band light curves in astronomy, an increasing number of time-series analysis techniques have been employed to reveal temporal patterns and underlying physical mechanisms of celestial objects. However, due to the different data characteristics and algorithmic ideas, it is rather difficult to select an appropriate method in practical tasks. So this paper provides an analysis of time-domain techniques for optical-band light curves in two parts. First, we categorize existing light-curve analysis methods into six major classes and conduct an in-depth review of each category, including their fundamental concepts, advantages, caveats, and representative applications. Secondly, we construct seven datasets based on stellar types using light-curve data from the OGLE-IV survey to uniformly evaluate the prediction performance of seven classical algorithms. Additionally, we assess the classification performance of four representative methods using the PLAsTiCC dataset. Finally, all source code and user manuals are made publicly available at $\langle$https://github.com/cymdd/LCModels$\rangle$, aiming to facilitate further research in this field.
We performed a spectroscopic observation of an erupting prominence occurred on the solar limb on 2015 May 8 in He i 7065 & Aring;, O i 7772 & Aring; triplet and Ca ii 8498 & Aring; lines to investigate differences in the Doppler velocity between ions and neutrals in a plasma strongly accelerated by the Lorentz force. We found that the ion-neutral velocity difference between Ca ii and He i reached an order of 15 km s(-1). On the other hand, the velocity difference between Ca ii and O i was significantly smaller than that between Ca ii and He i. This result can be interpreted as the formation of O i 7772 & Aring; lines in the erupting prominence is mainly contributed by the recombination from O ii ions through charge transfer with hydrogen atoms, resulting in a behavior close to ions. According to an order estimate of the collisional friction among He i atoms and protons, the observed velocity difference between Ca ii and He i implies the acceleration of the eruption reaches about 150 times the solar gravity. We propose a new method to evaluate the ionization degree of hydrogen from the velocity differences observed in Ca ii, He i, and O i lines.
We present results from a time-series photometric survey of the metal-poor globular cluster NGC 4372. Within a 24.'5 & times; 24.'5 field of view, 23 new variable stars were identified, increasing the total number of variables in our observed field to 44. The sample comprises 21 short-period pulsators, 18 eclipsing binaries, two ellipsoidal variables, one RR Lyrae star, one long-period variable, and one semi-regular variable. Notably, an RR Lyrae variable was discovered on the horizontal branch, representing the first identification of its class in this cluster. Using Gaia DR3 proper motions together with photometric criteria, we evaluated cluster membership and classified the short-period pulsators as 18 cluster SX Phoenicis (SX Phe) stars and three field S Scuti stars. From 14 fundamental-mode pulsators in the SX Phe sample, we derived the period-luminosity relation {V} = -3.942(+/- 0.304) log P + 12 . 858(+/- 0 . 402) , with a 1 sigma scatter of 0.087 mag. A multi-frequency analysis of these pulsators revealed three double-radial mode pulsators ( V11, V35, and V40) with period ratios typical of SX Phe stars. Among the eclipsing systems, three exhibit Algol-type light curves, whereas the remainder exhibit W UMa-type variability. For the W UMa binaries, Rucinski's M-V(log P, color ) calibrations together with Gaia DR3 proper motions suggest that V4, V5, V12, and V27 are consistent with cluster membership. V2 is classified as a Mira variable, exhibiting large-amplitude variability ( Delta V approximate to 3 . 28 mag) with a tentative period of P similar to 337d, as inferred from Gaia DR3 epoch photometry transformed to the Johnson V band. However, its position on the color-magnitude diagram and its proper motion imply that it is likely a field object. Our results provide an updated census and membership evaluation of variables in NGC 4372.
We observed the dwarf nova SS Cyg with the X-ray microcalorimeter onboard XRISM both in quiescence and outburst. The quiescence spectrum is explained with a multi-temperature optically thin thermal plasma emission model, characterized by He alpha and Ly alpha emission lines of Fe and Ly alpha lines of Si and S. We discovered redshifts of the Fe He alpha and Ly alpha lines that are larger than Ly alpha lines from Si and S. This indicates that the boundary layer ( BL) plasma accretes on to the white dwarf ( WD) accompanied by radiative cooling. Its radial accretion velocity estimated from the Fe redshift is 210-280 km s(-1) . Since a 6.4 keV Fe emission line is much narrower (ov= 561 km s(-1)) than that expected from the inner accretion disk rotation, we believe that it is emitted from the surface of the WD. The outburst spectrum can also be explained with the multi-temperature optically thin thermal plasma emission model, but is much softer than in quiescence and is dominated by He alpha lines. The Fe He alpha and Ly alpha lines and the 6.4 keV line are much broader than in quiescence, with Gaussian sigma values of 2390 and 3040 km s(-1) , respectively. This leads us to the idea that the hot plasma is a corona generated through magnetic activity in the optically thick BL that has strong differential rotation, and is anchored to the BL with the magnetic field. This picture is supported by the facts that the plasma follows the universal correlation between the temperature and the emission measure of the stellar flares, and the relation between the X-ray luminosity and the photospheric luminosity of low-mass stars. The fluorescent 6.4 keV line is emitted via fluorescence from the optically thick BL and/or from the equatorial accretion belt formed temporarily during the outburst.
High-resolution spectroscopy observations of sunspots offer a unique natural laboratory for detailed molecular spectroscopy. Calcium monohydride (CaH) is a vital spectroscopic tracer in cool stellar and solar environments, where its electronic transitions are used for line identification and temperature diagnostics, yet its high-excitation transitions remain poorly characterized. Using high-resolution sunspot umbral spectra obtained with the Brault Fourier-transform spectrometer at the McMath-Pierce telescope (Wallace et al. 1999, NSO Tech. Rep. 99-001), we investigated the A(2)Pi-X-2 Sigma(+) electronic transition of CaH in the 14400-14900(-1) region. We report the assignment of 224 spectral lines spanning vibrational bands with v ', v '' = 0-3; notably, 75 lines in the (3-3) band are reported here for the first time, and the identification of the remaining bands was extended to significantly higher rotational quantum numbers (J(max )approximate to 49.5$) compared to previous studies. Incorporating these new identifications into spectral simulations that account for overlapping TiO features, we aimed to reproduce the observed umbral spectrum and found modest but measurable improvement in the agreement between the simulated and observed spectra. Minimizing the residuals between observed and simulated spectra, we estimated an effective umbral temperature range of around 4000 K. We compare this effective temperature against those inferred from independent methods to show that molecular features primarily form in the cool umbral cores of the sunspots. This study demonstrates the utility of solar observations in studying the high-energy transitions that are challenging to reproduce in laboratory settings and the potential of molecular lines as sensitive "thermometers" for cool astronomical objects.
We investigate star formation activity in galaxies belonging to two Hickson Compact Groups (HCGs), HCG 56 and HCG 92 (Stephan's Quintet), both of which show clear evidence of interactions, using spectral energy distribution (SED) analysis across the near- to far-infrared range. By combining data from the Infrared Satellite AKARI, the Spitzer Space Telescope, and the Herschel Space Observatory, we examine how galactic interactions influence the physical conditions and the evolution of group members. The observed SEDs of member galaxies are compared with model SEDs representing both star-forming galaxies and active galactic nuclei (AGN). Star formation rates (SFRs) are estimated using two independent methods: (i) the strength of mid-infrared polycyclic aromatic hydrocarbon (PAH) bands and (ii) far-infrared luminosities attributed to star formation, as derived from the models. Although both methods yield generally consistent results, SFRs based on PAH features are systematically lower, possibly due to the PAH destruction in some interacting galaxies. When plotted against the stellar mass, all member galaxies are found below the main sequence of star-forming galaxies in the SDSS field, suggesting that interaction-induced starbursts are not seen in HCG 56 and HCG 92.
The amount of the interstellar gas in the Galaxy has been conventionally estimated through observations at various wavelengths. The estimation of the total hydrogen column density (N_ m H) depends on assumptions such as temperature. The X-ray absorption process is the photoelectric absorption, which depends on the number of atoms to encounter X-ray photons, and hence X-ray observations would be able to derive the N-H values independently on the condition of the interstellar matter. We measured the Galactic absorption using clusters of galaxies at the low Galactic latitude. Comparing the observed N-H with the calculated N-H values from H i and CO intensities indicates that the observed values are systematically larger than the calculated values. The observed N-H values at high Galactic latitude (N-H < 10(22) cm(-2)) are comparable to those estimated from N-H, small I and optical reddening values using the method by Willingale et al. (2013, MNRAS, 431, 394), but the values near to the Galactic plane (N-H > 10(22) cm(-2)) are larger than the estimated ones. The dust optical depth at 353 GHz, au _353, and the observed N-H values are expressed by a linear function of N-H=(1.01-1.59)x 10(26) au _353 cm(-2 )even at N-H > 10(23) cm(-2). We also confirmed a linear correlation between the optical reddening, E(B-V), and the N-H values expressed by N-H=(6.3-9.5)x 10(21) E(B-V) m cm(-2). This work is an additional and independent test of the relation among the amount of interstellar gas, the optical depth, and the optical reddening.
Diffuse far-infrared synchrotron emission filling the northern inner lobe of the radio galaxy Centaurus A is investigated with the Spectral and Photometric Imaging Receiver onboard the Herschel observatory at its three photometric bands. The far-infrared flux density spatially integrated over the lobe is measured as S-v= 1 . 63 +/- 0 . 05 Jy at the wavelength of 500 & micro;m ( the frequency of 600 GHz). A comparison between the far-infrared spectral index derived with Herschel (alpha = 1 . 32 +/- 0 . 19 ) and the radio index (alpha = 0 . 66 +/- 0 . 04 ) suggests a spectral break between these frequency ranges. The change of the spectral index through the break is indicated to be consistent with that of the standard cooling break (Delta alpha = 0 . 5 ) predicted for particle acceleration under the continuous energy injection condition. A broken power-law model incorporating the standard cooling break yields the break frequency as nu(b )= 218 +/- 83 GHz. From the measured cooling break frequency, the magnetic field of the northern inner lobe is evaluated as B less than or similar to 100 & micro;G. It is quantitatively estimated that the adiabatic cooling puts only a minor impact on the derived magnetic field. This magnetic field is higher than that under the minimum-energy condition by more than a factor of 5. In addition, the derived magnetic field of the lobe is suggested to be at least by a factor of 4 stronger than that of the inner-jet region implied in the previous very-high-energy gamma-ray study. Even if the line-of-sight orientation of the lobe is considered in its possible extreme case, the magnetic field is found to be reduced only by a factor of 2, and the above arguments about the strong magnetic field basically holds. The science impact of this result is discussed from the viewpoints of jet energetics, and of ultra-high energy cosmic rays.
Three-dimensional (3D) simulations of neutrino-driven core-collapse supernovae are among the most reliable tools for predicting explosion outcome. However, their high computational cost limits systematic surveys over large progenitor samples. We test how well a fast one-dimensional (1D) approach captures progenitor explodability. We use a parameter-optimized semi-analytic 1D explosion model based on M & uuml;ller et al. (2016, MNRAS, 460, 742) calibrated to the 3D results of Burrows et al. (2024, ApJ, 964, L16) as an adopted reference set. We compare the model's explodability predictions with commonly used structure-based criteria: compactness, the free-fall mass coordinate, and the two-parameter $\mu _4$-$M_4$ criterion. Our analysis shows that the semi-analytic model can reproduce the trends seen in this adopted 3D calibration set by adjusting physically meaningful parameters. This provides a more direct way to examine the physics that controls explodability than traditional structure-based criteria. We identify where the semi-analytic model agrees with these criteria, where it differs, and which physical trends explain the differences. This work clarifies the strengths and limitations of structure-based explodability criteria by evaluating them against a parameter-optimized, neutrino-driven semi-analytic model.
A neutron star is born as a hot, lepton-rich protoneutron star (PNS) and cools via neutrino emission, eventually allowing heavy ions in the outer layers to crystallize into a solid crust. We develop a simple analytic estimate for the onset time of this crust formation during the late, post-convective PNS cooling phase. Using a diffusion-based neutrino luminosity and the resulting entropy evolution together with an approximately isentropic interior structure, we obtain the time-dependent density and temperature at the neutrinosphere. We then impose the Coulomb crystallization condition for heavy nuclei, expressed through the Coulomb coupling parameter, and determine when the neutrinosphere temperature first falls below the crystallization threshold evaluated at the neutrinosphere density. This procedure yields closed expressions for the entropy at crystallization and the corresponding crust-formation time, with explicit dependence on the PNS mass and radius, an effective diffusion/cooling normalization, and composition parameters such as the ionic charge Z and heavy-nuclei mass fraction. For canonical microphysics, we find that the first solid phase typically appears at t(crust) similar to 100-500 s. These closed-form scalings provide a useful late-time analytic benchmark for the onset of crust formation and clarify its dependence on PNS and composition parameters.
