Solar and Stellar Astrophysics
Sinking and spreading of metal pollution in magnetic white dwarfs
Elad Shiftan and Sivan Ginzburg
Observations of
magnetic polluted white dwarfs indicate that most of them have higher concentrations of metals near the poles compared to lower latitudes. Maintaining such abundance gradients requires gravitational sinking times $t_\downarrow$ below the convection zone that are shorter than the horizontal spreading time $t_\leftrightarrow$ across the surface by convective eddies. We show analytically that $t_\downarrow/t_\leftrightarrow\propto T^{8/3}$, where $T$ is the temperature at the base of the convection zone, which rises by more than an order of magnitude as convection penetrates deeper into the atmosphere. Correspondingly, $t_\downarrow/t_\leftrightarrow$ jumps by several orders of magnitude, clearly delineating between hot white dwarfs with abundance variations and cold ones with homogenous surfaces. We incorporate
magnetic fields self-consistently into the stellar structure and compute for the first time the sinking to spreading time-scale ratio as a function of $B$.
Magnetic white dwarfs have shallower convection zones at a given $T_{\rm eff}$, and the inward penetration of convection shifts to lower $T_{\rm eff}$. Quantitatively, $B\sim 10^5\textrm{ G}$ extends the range for enhanced abundance patches from $T_{\rm eff}\gtrsim 30\,000 \textrm{ K}$ ($13\,000\textrm{ K}$) to $T_{\rm eff}\gtrsim 15\,000 \textrm{ K}$ ($6000\textrm{ K}$) for helium (hydrogen) dominated atmospheres, which is insufficient to explain the observed patchy white dwarfs, which are even colder. A possible solution is variability in the
accretion rate on a time-scale of a decade, as recently detected in another white dwarf.
Read the full abstract ▾
Solar and Stellar Astrophysics
Accretion Rates and Thermohaline Convection in Polluted White Dwarfs
J. R. Fuentes, Matias Castro-Tapia, Jim Fuller et al. (+1 more)
Polluted white dwarfs provide a unique window into the composition of exoplanetary material, but interpreting their surface abundances requires a quantitative understanding of the mixing processes in their envelopes.
Accretion of metal-rich debris onto hydrogen-rich white dwarfs drives thermohaline (fingering) convection in the underlying radiative zone. Previous studies have modeled this as enhanced diffusive transport, often inferring mass
accretion rates, $\dot{M}_{\rm acc}$, that exceed constraints from X-ray observations. Here we develop a time-dependent model that treats thermohaline mixing as a propagating front whose
evolution is coupled self-consistently to the surface abundance of heavy elements. We perform hydrodynamical simulations which demonstrate that thermohaline mixing drives the composition gradient towards marginal stability. Using this condition, we derive analytic solutions in shallow and deep stratification regimes, finding that the mixed layer depth, $h$, and surface abundance, $X_{\rm surf}$, both scale as $t^{1/2}$ at early times, transitioning to $h \propto t^{4/27}$ and $X_{\rm surf} \propto t^{10/27}$ at later times. The mixed layer reaches depths of only $\sim 100$ km over $10^5$ yr and, without gravitational settling, never reaches a steady state. Including settling leads to an
equilibrium surface abundance scaling as $X_{\rm surf, eq} \propto \dot{M}_{\rm acc}^{30/43}$. Applied to G 29–38, the model matches the observed heavy-element abundance for $\dot{M}_{\rm acc} \sim 2\times 10^9$–$4\times 10^{9}~\mathrm{g~s^{-1}}$, in better agreement with X-ray constraints than prior estimates incorporating thermohaline mixing. We also present a general scaling relation for inferring
accretion rates directly from observed surface abundances and stellar properties, giving a practical prescription for other polluted white dwarfs.
Read the full abstract ▾
All authors J. R. Fuentes, Matias Castro-Tapia, Jim Fuller, Marcus King
Solar and Stellar Astrophysics
From spectroscopic abundances to evolutionary [$\alpha$/Fe] in stellar models
Pedro Diaz Reeve and Aldo Serenelli
Large-scale, high-resolution spectroscopic surveys map detailed chemical abundance patterns for millions of
stars. However, libraries of stellar
evolution models and isochrones still rely on a simplified description of chemical abundances, generally assuming either solar-scaled compositions or a constant enrichment for all $\alpha$-elements. Moreover, the definition of $\alpha$-enrichment is survey-dependent and is not necessarily the most relevant quantity for stellar structure and
evolution. In the era of precision stellar astrophysics, stellar models need to better account for the wealth of chemical information provided by spectroscopic surveys. We develop a perturbative method to compute stellar
evolution tracks for
stars with arbitrary patterns of $\alpha$-elements. We quantify the response of stellar evolutionary tracks to variations of individual $\alpha$-elements through
polynomial expansions, which can be linearly combined to produce synthetic tracks for a given abundance pattern. We also introduce the evolutionary $\alpha$-enhancement, [$\alpha$/Fe]$_{\rm ev}$, a constant enhancement for all $\alpha$-elements that reproduces the impact of an observed abundance pattern on stellar models. We validate both methods using
stars with detailed APOGEE abundances and quantify the differences between spectroscopic [$\alpha$/Fe] and [$\alpha$/Fe]$_{\rm ev}$ for different surveys. We identify a minimal set of chemical elements required for accurate stellar models and present ALCHEMY, a simple and fast tool to compute [$\alpha$/Fe]$_{\rm ev}$ for general $\alpha$-element abundance patterns.
Read the full abstract ▾
Solar and Stellar Astrophysics
Extremes of solar spectral irradiance in the SORCE/XPS record
Enzo Brasil, Cira E. G. Otiniano, Carolyne Brito et al. (+2 more)
Extreme and rare changes in space mission solar irradiance records are scientifically relevant but difficult to quantify because these records are finite, instrument dependent, and affected by observational gaps and time varying measurement quality. We evaluated extreme daily logarithmic changes in the band integrated 0.1-7.0 nm irradiance measured by photodiode 7 of the Solar Radiation and
Climate Experiment/X-Ray Photometer System (SORCE/XPS) from 2005 to 2019. After constructing a regular daily series by linear interpolation, we analyzed daily logarithmic changes in irradiance and fitted stationary Generalized Extreme Value models to 60 day block maxima and transformed 15 day block minima. Block lengths were selected using Ljung-Box diagnostics and sample autocorrelation functions. Maximum likelihood estimation was used as the primary inferential method, with probability weighted moments as a sensitivity check. The maximum likelihood GEV shape estimates were 0.1661 for maxima and 0.2928 for transformed minima, with closely aligned estimates under the two fitting methods. These positive point estimates are compatible with Fréchet type tails under the selected block constructions. Annualized return levels provide interpretable summaries of extreme relative increases and reductions, but estimates for long return periods remain strongly dependent on extrapolation beyond the 15 year record. Reported measurement precision and absolute uncertainty were used to qualify the interpretation of the fitted tails and were not propagated through the likelihood. By combining EVT based tail modeling with explicit consideration of measurement precision, absolute uncertainty, interpolation, and mission data gaps, the analysis provides an uncertainty aware astrostatistical baseline for extreme value inference from processed solar mission records.
Read the full abstract ▾
All authors Enzo Brasil, Cira E. G. Otiniano, Carolyne Brito, Beatriz Albernaz, Fidel Morales
Solar and Stellar Astrophysics
Study of Butterfly-Shaped Coronal Hole Evolution Across the Solar Disk
Bhairab Ale, Khagendra Katuwal and Shiv Narayan Yadav
We studied the
evolution of a butterfly-shaped coronal hole (CH) observed from 2025 September 8 to 14 using SDO/AIA 193~Å\ images and SDO/HMI line-of-sight magnetograms. The CH boundary was identified using a fixed 100~DN intensity threshold, and its area, mean EUV intensity, and total unsigned
magnetic flux were tracked across the solar disk. As the CH approached the central meridian, its area increased from approximately $7.70\times10^{16}$ to $1.63\times10^{17}$~m$^{2}$ and its unsigned
magnetic flux from $8.68\times10^{21}$ to $1.91\times10^{22}$~Mx, while the mean 193~Å\ intensity decreased from about 61 to 45~DN. The area and unsigned flux showed similar temporal trends, whereas the intensity varied oppositely. Near central-meridian passage, these quantities remained relatively stable for several days. A high-speed solar-wind stream was detected at 1~AU about 2–4 days later, reaching 600–750~km~s$^{-1}$, consistent with the CH being its likely solar source. These results link the morphological, radiative, and
magnetic evolution of the CH with the subsequent high-speed solar-wind stream.
Read the full abstract ▾
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
Magnetohydrodynamics of charged interstellar dust. Multifluid models and study of the linear modes
Gabriel Verrier, Patrick Hennebelle, Ugo Lebreuilly et al. (+1 more)
Interstellar grains play key roles in
star and
planet formation, including the coupling of the gas to the
magnetic field during the protostellar collapse. These roles depend on the local grain size distribution, which requires a multifluid treatment of charged dust. We aim to understand the fundamental physics of the dynamics of a dust distribution in interaction with the gas and the
magnetic field. In particular, the purpose is to characterize the (de)coupling conditions of these different components. We provide a multifluid model of charged dust which accounts for the inertia of the grains. A chemical network is used to simulate the charge
equilibrium in collapsing protostellar cores. We compute the Alfven modes and the magnetosonic modes to understand the coupling regimes between the gas, the dust fluids, and the
magnetic field. We also analyze and compare to the predictions of existing models, that are the neutral dust multifluid and the standard non-ideal magnetohydrodynamics. The charged multifluid model agrees with non-ideal magnetohydrodynamics on the larger scales of a collapsing dense core and the forming disk, while we successfully extend to new regimes where the inertia of dust grains matters. We found that high charge-to-mass dust grains carry the propagation of magnetohydrodynamical waves in protostellar envelopes. We provide analytical expressions of the speed of these waves depending on the dust distribution. The magnetocompressive perturbations lead to local dust-to-gas ratio variations at au scales. A theoretical understanding of the dynamics of a charged dust distribution is provided in the linear regime. The closed set of magnetohydrodynamics equations can be implemented in numerical codes to explore nonlinear effects during the protostellar collapse such as
turbulence, angular momentum transport and
magnetic dust clumping.
Read the full abstract ▾
All authors Gabriel Verrier, Patrick Hennebelle, Ugo Lebreuilly, Valentin Vallucci-Goy
Solar and Stellar Astrophysics
The umbrella effect: Magnetic canopy topology modulates spatially averaged chromospheric three-minute power
Shahin Jafarzadeh, David B. Jess, Marco Stangalini et al. (+11 more)
Three-minute ($\sim$5 mHz) oscillations are a prominent signature of wave propagation in the solar chromosphere, but their measured power can vary substantially between full-disc observations and small, high-resolution fields of view. We investigate whether chromospheric
magnetic canopy
topology, particularly its lateral continuity and areal filling, modulates field-of-view-averaged three-minute power. We analyse H$\alpha$ and Ca II 8542 Å spectral imaging from the Swedish 1-m Solar
Telescope, comparing canopy-poor quiet-Sun scenes with canopy-dominated active-region environments, complemented by radiative-MHD Bifrost simulations of canopy-poor and canopy-rich atmospheres. We compute field-of-view-averaged power spectra from fixed-wavelength intensities and bisector-derived velocities in the observations, and from synthetic intensities, velocities, and temperature proxies in the simulations. We also quantify the relation between integrated 3-5 mHz excess power and canopy filling factor, using HMI-based
magnetic-field extrapolations for the observations. In both observations and simulations, canopy-poor scenes show clear 3-5 mHz power enhancements, whereas canopy-dominated scenes show strongly reduced measured power. The trend is present in H$\alpha$ and Ca II 8542 Å intensities and is supported by complementary velocity and temperature proxies. Integrated 3-5 mHz excess power decreases with increasing canopy filling factor. We conclude that chromospheric field-of-view-averaged three-minute power is a
topology-weighted observable: dense, laterally continuous
magnetic canopies can strongly reduce the measured large-scale three-minute signature without requiring the absence of local wave activity. This provides a practical criterion for interpreting chromospheric oscillation power as a proxy for atmospheric wave energy in the Sun and in magnetised cool-
star atmospheres.
Read the full abstract ▾
All authors Shahin Jafarzadeh, David B. Jess, Marco Stangalini, Bernhard Fleck, Richard J. Morton, Samuel D. T. Grant, Peter H. Keys, Luc Rouppe van der Voort, Sven Wedemeyer, Tiago M. D. Pereira, Mikołaj Szydlarski, Elias R. Udnæs, Thomas Wiegelmann, Markus Roth
Solar and Stellar Astrophysics
Astrometric modeling of unresolved variable binary systems. II. Application to Gaia epoch astrometry of nearby pulsating and convective red giants
L. Decin, K. Sivkova, P. Kervella et al. (+2 more)
(Abbreviated) The interpretation of high-precision astrometry for intrinsically variable
stars remains challenging, particularly for unresolved binary systems containing asymptotic giant branch (AGB)
stars. In such systems, large-amplitude pulsations and evolving convective surface structures induce time-dependent photocentre displacements that perturb the observed orbital motion. At the same time, Gaia DR4 epoch astrometry offers the prospect of deriving accurate orbital solutions and parallaxes for nearby unresolved AGB binaries. Building upon the variability-induced mover (VIM) framework, we extend the astrometric model for unresolved evolved binaries by combining Keplerian photocentre motion, pulsation-induced flux-dependent photocentre shifts, and convection-induced photocentre motion. In the forward simulations, convection is represented either by
stochastic photocentre displacements drawn from an exponential correlation function or by photocentre time series extracted from 3D radiation-hydrodynamic simulations. We then test a
retrieval framework that fits the orbital and VIM signal while incorporating a red-noise covariance
matrix to account for correlated astrometric residuals produced by convection. We show that Gaia epoch astrometry can recover reliable orbital and astrometric parameters for unresolved AGB binaries despite strong pulsation- and convection-induced photocentre variability. Pulsation-induced variability produces a coherent VIM signal that can be modeled jointly with the Keplerian photocentre orbit, while convection-induced photocentre motion behaves primarily as temporally correlated astrometric noise.
Retrievals that ignore this correlated component lead to biased proper motions and parallaxes, whereas the inclusion of a physically motivated red-noise covariance model enables accurate recovery of the underlying orbital solution and astrometric parameters.
Read the full abstract ▾
All authors L. Decin, K. Sivkova, P. Kervella, A. Chiavassa, E. Beguin
Solar and Stellar Astrophysics
Interferometric Survey of Stellar Parameters: Towards homogeneous FGK stars parameters and surface-brightness color relation in the context of PLATO space mission
Romina V. Ibañez Bustos, Denis Mourard, Nicolas Nardetto et al. (+20 more)
The estimation of stellar angular diameters can be performed from the surface brightness - color relation (SBCR) and photometry. The SBCR have been considered by the PLATO space mission as an independent empirical alternative for estimating stellar radii of FGK
stars. In this context, we have implemented an homogeneous approach not only for calibrating the SBCR for FGK-IV/V
stars but, also for determining their fundamental parameters in order to place the
stars reliably on the HR diagram and to study their impact on the SBCR. We have performed interferometric observations of 18 quiescent FGK-IV/V
stars in the Gaia color range of $3.088 \leq G \leq 5.498$. For the first time, we used 3 different interferometers operating in the $R$, $H$ , and $K$ bands to measure polychromatic limb-darkened angular diameters (LDAD). In parallel, by using public domain spectra we have estimated the stellar parameters ($T_{eff}$, $log g$ and Z) by using the open python tool iSpec. We achieved an average accuracy of 2.3% for the LDAD based on polychromatic observations. However, we have observed that our SBCR does not follow the calibration of the relation between surface brightness and color in Gaia found in the literature. Furthermore, we found that $log g$ and $Z$ have no impact on the SBC relation; given the characteristics of our sample of quiescent
stars, it constitutes an ideal set of targets for conducting a new SBCR calibration within the framework of the PLATO space mission. In this context, we reported a SBCR calibration with $\sigma_{RMS} = $ 0.012, 0.009, 0.009 in the $G, G_{BP}$ and $G_{RP}$ Gaia bands, respectively. This article is part of a series of papers reporting the first results obtained using a polychromatic approach to measure LDAD, employing a fully homogeneous methodology for both determining the fundamental parameters of
stars and measuring the LDAD, $\theta_{LD}$.
Read the full abstract ▾
All authors Romina V. Ibañez Bustos, Denis Mourard, Nicolas Nardetto, Jeremy Jones, Nayeem Ebrahimkutty, Juraj Jonák, Hugo Nowacki, Mathieu Vrard, Philippe Berio, Julien Dejonghe, Roxanne Ligi, Frédéric Morand, David Salabert, Orlagh Creevey, Armando Domiciano de Souza, Manon Bailleul, Karine Perraut, Markus Wittkowski, John D. Monnier, Stefan Kraus, Narsireddy Anugu, Mayra Gutierrez, Noura Ibrahim
Solar and Stellar Astrophysics
Joint Observations of PTPS Targets (JOTA). Combined spectroscopic and photometric analysis of 16 SB1 systems
Robert Jaros, Andrzje Niedzielski, Sohaib Ali et al. (+9 more)
Context. The Pennsylvania-Toruń
Planet Search, which operates on a sample of $\sim$1000 northern-hemisphere
stars, has been underway since 2004.
Stars with radial velocity (RV) amplitudes exceeding 2 km s$^{-1}$ represent a backup subprogram sample dedicated to monitoring binary
stars with multiple instruments. Aims. We used almost 21 years of combined RV measurements to search for Doppler signals consistent with stellar or brown dwarf companions and to produce a catalog of both known and previously unpublished binary
stars in our
planet-search sample. Methods. We analyzed the combined RV measurements, searching for stellar companions and obtaining orbital solutions for both known and new binary systems. We also searched for periods in available long-term photometric monitoring data from All Sky Automated Survey (ASAS), and applied Gaia astrometric data whenever available. Results. We report the results of long-term RV monitoring of 16 systems: new detections of low-mass companions to 11
stars and updated orbital elements based on combined sets of our new and literature data for five systems. For two objects (TYC 3318-00789-1 and TYC 3318-01538-1), we find evidence of activity or the influence of another unseen companion, possibly due to line-profile variations or unresolved spectral contamination. We present true masses for three systems in our sample: TYC 1931-1040-1, TYC 3451- 1449-1, and TYC 3667-1636-1. We obtained these masses using Gaia DR3 non-single
star data.
Read the full abstract ▾
All authors Robert Jaros, Andrzje Niedzielski, Sohaib Ali, Divyansh Srivastava, Julia Sierzputowska, Monika Adamów, Jorge Lillo-Box, Dmytro Orikhovskyi, Aleksander Wolszczan, Eva Villaver, Theodor Pribulla, Martin Vaňko
Solar and Stellar Astrophysics
Equilibrium \(\mathrm{H}_2^+/\mathrm{H}^-\) Abundance Ratios in MARCS Atmosphere Models
Aiganym Sarsembayeva and Hernando Quevedo
We investigate the
equilibrium abundance ratio of the molecular hydrogen ion \(\mathrm{H}_2^+\) and the negative hydrogen ion \(\mathrm{H}^-\) in stellar atmospheres using compact Saha-type
equilibrium expressions and layer-by-layer partial pressures from MARCS model atmospheres. The analysis distinguishes the temperature-dependent coefficient ratio \(K_{\mathrm{H}_2^+}(T)/K_{\mathrm{H}^-}(T)\) from the full abundance ratio, which also depends on the local ionisation factor \(N_{\mathrm{H}^+}/N_e\). The internal partition function \(Z_{\mathrm{H}_2^+}(T)\) is included in the \(\mathrm{H}_2^+\)
equilibrium coefficient. We processed \(51{,}994\) MARCS models, corresponding to \(2{,}911{,}664\) atmospheric layers, and computed \(N(\mathrm{H}_2^+)/N(\mathrm{H}^-)\) directly from the tabulated
equilibrium partial pressures, constructing the first systematic map of this ratio across the MARCS grid. \(\mathrm{H}_2^+\) exceeds \(\mathrm{H}^-\) in \(827{,}350\) layers, corresponding to \(F=0.284\), or \(28.4\%\) of all analysed layers. Although \(\mathrm{H}^-\) remains dominant in the global logarithmic mean, with \(\langle \log_{10}[N(\mathrm{H}_2^+)/N(\mathrm{H}^-)] \rangle=-4.229\), \(\mathrm{H}_2^+\) becomes comparable to or more abundant than \(\mathrm{H}^-\) in a substantial subset of layers. Its relative significance increases toward higher \(T_{\mathrm{eff}}\), lower \([\mathrm{Fe}/\mathrm{H}]\), and deeper layers. The balance is therefore controlled by the combined local thermodynamic and ionisation structure, not by temperature alone. These ratios are
equilibrium abundance diagnostics and do not imply opacity dominance; assessing opacity requires wavelength-dependent cross-sections and radiative-transfer calculations.
Read the full abstract ▾
Solar and Stellar Astrophysics
Phosphorus abundances and multi-element co-enrichment in nearby FGK stars
Dario Esposito, Giovanni Covone, Donato Giovannelli et al. (+9 more)
The distribution of bio-essential elements is key to assessing the chemical fertility of galactic environments. We analyse phosphorus abundances for 233 nearby FGK
stars from the Hypatia Catalog, separating thin- and thick-disk populations. We study [P/Fe] as a function of [Fe/H] and other elemental abundances using non-parametric tests and bootstrap resampling, and we examine residual correlations at fixed [Fe/H] together with molar ratios involving P. We find a [P/Fe]-[Fe/H] trend broadly similar to that of alpha elements, supporting a dominant origin in core-collapse
supernovae, while deviations point to additional nucleosynthetic channels. Phosphorus shows strong positive correlations with several CHNOPS, alpha, and Fe-peak elements, especially in the thin disk. These co-enrichment patterns remain significant at fixed [Fe/H], indicating that they are not a trivial consequence of global
metallicity. Thin-disk
stars are also more enriched than thick-disk
stars in many elements. The solar P/Mg and P/Si ratios are representative of the local stellar population, whereas solar P/O is relatively elevated. Overall, phosphorus emerges as a tracer of genuine multi-element co-enrichment and of the chemical fertility of the solar neighbourhood.
Read the full abstract ▾
All authors Dario Esposito, Giovanni Covone, Donato Giovannelli, Paola Manini, Christian Magliano, Laura Inno, Luca Cacciapuoti, Víctor M. Rivilla, Vito Saggese, Leonardo Testi, Emanuele Cristiano, Luca Tonietti
Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE
SN 2019cqc: A Hydrogen-rich Superluminous Supernova Showing Electron-Scattering Signatures
Dinesh Hebbar, Rupak Roy, Matt Nicholl et al. (+15 more)
Hydrogen-rich superluminous
supernovae without narrow emission lines (SLSNe-II) are rare transients whose powering mechanisms remain debated, particularly the role of circumstellar medium (CSM) interaction. We present photometric and spectroscopic observations of SN 2019cqc to investigate its power source and progenitor mass loss. We model the lightcurve using MOSFiT with the csm and csmni models to constrain the explosion and CSM parameters. SN 2019cqc peaked at $M_g = -20.21 \pm 0.07$ and emitted $\sim 1.7 \times 10^{50}\,\mathrm{erg}$ of energy in the form of radiation. Photometric and spectroscopic modeling indicates that CSM interaction dominates in both scenarios, with best-fit CSM and ejecta masses of $\sim 4.5~ M_\odot$ and $\sim 32~ M_\odot$, respectively. The inferred CSM properties imply an extreme eruptive mass loss at a rate of $\sim 0.2--0.3 ~M_\odot\,\mathrm{yr^{-1}}$ in the years preceding the core collapse, consistent with a variable progenitor of luminous blue variable progenitor. We observe a persistent blueshifted asymmetry in the H$\alpha$ emission line. At early times ($\lesssim +110$~d), this is attributed to electron scattering with bulk Velocity of ejecta, while the profile at late epochs ($\gtrsim +402$~d onward) suggests the subsequent formation of dust in the ejecta. Additionally, we identify a distinct, short-lived feature at $\sim$ 4600 Å , likely a blend of ionized C III/N III lines powered by the interaction of the SN-shock with the extended atmosphere.
Read the full abstract ▾
All authors Dinesh Hebbar, Rupak Roy, Matt Nicholl, Jesper Sollerman, Joseph P Anderson, Mariusz Gromadzki, D. Andrew Howell, Tuomas Kangas, Seppo Mattila, Daichi Hiramatsu, Avishay Gal-Yam, Edo Berger, K. Azalee Bostroem, Ting-Wan Chen, Joseph Farah, Sebastian Gomez, Curtis McCully, Jeonghee Rho
Solar and Stellar Astrophysics
Systematic and Statistical Properties of Prominence Eruptions on the M-dwarf YZ CMi
Yuto Kajikiya, Kosuke Namekata, Yuta Notsu et al. (+4 more)
M-dwarfs produce frequent
flares, and their associated mass ejections are expected to significantly affect the habitability of close-in
exoplanets. Recent spectroscopic observations have revealed several prominence eruptions-indicative of stellar mass ejections-on M-dwarfs through Doppler shifts of the H$\alpha$ line. However, systematic and statistical studies, particularly regarding their association with white-light
flares, have been limited due to the lack of intensive and continuous simultaneous photometric and spectroscopic monitoring of the same target
star. We conducted one month of continuous spectroscopic observations of the active M-dwarf YZ CMi using the 3.8-m Seimei
telescope with an unprecedentedly high time cadence of $\sim$1 min, simultaneously with TESS. We detected four prominence eruptions, among which two events showed rapid, short-duration eruptions with velocities of $\sim$300-500 km s$^{-1}$ and durations of $\sim$5 min. Such short-duration events may have been missed in previous observations due to insufficient time cadence. We further performed a systematic analysis using 35 H$\alpha$
flares on YZ CMi observed simultaneously with TESS. Notably, most prominence eruptions (6 out of 7) were not associated with detectable white-light
flares. This result suggests that most observed prominence eruptions on M-dwarfs may have occurred near the stellar limb, where white-light
flares are difficult to detect, which may imply a potential observational bias in their detectability due to low contrast with the background emission. These first statistical constraints, together with the discovery of rapid, short-duration prominence eruptions, indicate that previous observations may have underestimated both the frequency and velocities of mass ejections on M-dwarfs due to observational biases and highlight the necessity of reassessing their impact on close-in
exoplanets.
Read the full abstract ▾
All authors Yuto Kajikiya, Kosuke Namekata, Yuta Notsu, Kai Ikuta, Hiroyuki Maehara, Bunei Sato, Daisaku Nogami
Solar and Stellar Astrophysics
OB stars identified in LAMOST Data Release 10
Guang Yang, Zhicun Liu, Xiao-Long Wang et al. (+2 more)
A large sample of OB
stars plays an important role in studying the stellar parameters of massive
stars, as well as the formation and
evolution of the Milky Way. With the help of the Large Sky Area Multi-Object Fiber Spectroscopic
Telescope (LAMOST) Data Release 10 (DR10), we are able to construct a large sample of OB
stars with spectroscopic data. In this study, we identify 48,463 spectra of 34,550 OB
stars from LAMOST DR10, based on the Hertzsprung-Russell (H-R) diagram constructed with Gaia DR3 data and spectral line indices measured from LAMOST DR10 low-resolution spectra. Among these, 6907 OB
stars are newly identified. We use the MKCLASS tool to derive the spectral subtypes of the OB sample. The spatial distribution of 25,287 OB
stars and the Toomre diagram of 20,397 OB
stars indicate that the majority of these
stars are located in the Galactic disk. Based on their peculiar velocities, we identify 1960 runaway
star candidates.
Read the full abstract ▾
All authors Guang Yang, Zhicun Liu, Xiao-Long Wang, Yanjun Guo, Wenyuan Cui
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
Empirical Constraints on the CO Snowline Transition in HD 163296: The Local CO Column and $^{13}$C$^{18}$O Optical Depth
Chunhua Qi, Takahiro Ueda, David J. Wilner et al. (+1 more)
CO isotopologue emission is widely used to infer gas masses and volatile carbon abundances in protoplanetary disks, but converting line emission into a CO column depends on optical depth, temperature structure, linewidth, and isotope ratios. Inferring CO/H$_2$ additionally requires an independent constraint on the local hydrogen column. We use high-resolution $^{13}$C$^{18}$O $2$-$1$ observations of HD 163296 to derive a spatially localized empirical constraint on the CO column at the resolved CO snowline edge. We focus on the 70-75 au annulus, on the inner, high-column side of the observed profile steepening near 75 au. Using RADEX slab calculations conditioned on a two-dimensional temperature structure, we infer an effective beam-averaged CO column from the absolute integrated intensity. Across representative temperatures, isotope-ratio pairs, and effective local linewidths of 0.30 and 0.50 km s$^{-1}$, we find $N_{\rm CO}^{\rm beam}=(1.6-2.4)\times10^{20}$ cm$^{-2}$ and $^{13}$C$^{18}$O line-center optical depths $\tau=0.39-0.97$. Thus, even this rare isotopologue is not safely optically thin at the snowline edge. Adopting $N_{\rm H2}=2.5\times10^{24}$ cm$^{-2}$ from a published parametric gas surface-density profile gives the conditional abundance ${\rm CO/H_2}=(6.4-9.5)\times10^{-5}$. A beam-forward radial-profile analysis gives consistent columns, and a physical disk model with a near-canonical warm-layer CO abundance supplies a comparable CO column. The measurement is consistent with the higher C$^{17}$O-based MAPS estimate. For the adopted hydrogen column, the inferred CO/H$_2$ ratio is consistent with a near-canonical abundance on the warm side of the snowline.
Read the full abstract ▾
All authors Chunhua Qi, Takahiro Ueda, David J. Wilner, Catherine C. Espaillat
Solar and Stellar Astrophysics
Moment-based formulas for the transport coefficients
J.-F. Wang and G. Qin
The coefficients of the transport equations, describing the propagation features, are particularly important in astrophysics, interplanetary physics, and experimental
plasma physics. In this paper, the variable-dependent
diffusion coefficients are investigated. For the momentum transport equations, we find that the coefficients are related to statistical quantities, some of which are new. In addition, these coefficients take logarithmic forms, which are different from the results derived in previous papers. For isotropic pitch-angle scattering, we also obtain a formula that takes a logarithmic form. For fractional transport equations, the coefficients expressed in terms of the moments are obtained from the governing equations.
Read the full abstract ▾