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Physics Astrophysics Solar and Stellar Astrophysics

astro-ph.SR Watch Solar and Stellar Astrophysics

Monday 17 August

Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

SN 2023gfo: A Peculiar Type IIP Supernova with High Luminosity and Normal Plateau Duration

Riko Namba, Masayuki Yamanaka, Keiichi Maeda et al. (+9 more)

We present near-infrared (NIR) and optical observations of the highly reddened Type IIP supernova (SN) 2023gfo in the nearby galaxy NGC 4995 ($d = 26.4 \pm 3.2$ Mpc), which reached a high peak luminosity of $M_V = -18.6$ mag. The SN was initially detected as a faint red event, with $B-V = 0.8$ mag at the beginning of the plateau phase. By comparison with template, we estimate a total extinction of $A_V = 2.1$ mag. After correcting for this extinction, we derive a peak quasi-bolometric luminosity of $(5.9 \pm 1.5)\times10^{42}$ erg s$^{-1}$, placing this event among the most luminous SNe IIP, while its plateau duration remains within the normal range. The early-phase optical spectrum exhibits a P-Cygni profile of H$\alpha$, with a broad absorption of $V$ = $13{,}800$ km s$^{-1}$, which is among the highest observed for SNe IIP at comparable epochs. The high luminosity and the normal plateau duration suggest that this event represents an outlier. Applying an analytical model, we infer an unusually large progenitor radius. This may indicate that the progenitor experienced an extreme energy injection from the core to the envelope shortly before explosion, resulting in a substantially inflated radius. While ejecta-circumstellar matter (CSM) interaction could in principle account for the high luminosity, we find no observational evidence supporting strong interaction.
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All authors Riko Namba, Masayuki Yamanaka, Keiichi Maeda, Avinash Singh, Kenta Taguchi, Takahiro Nagayama, Miho Kawabata, Koji S. Kawabata, Tatsuya Nakaoka, Devendra Sahu, Anjasha Gangopadhyay, G. C. Anupama

Sunday 16 August

Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

A High-Resolution Spectroscopic Survey of Directly Imaged Companion Hosts: III. Characterization of the Cold Imaged Planet Hosts AF Lep A and $\epsilon$ Indi A

Aneesh Baburaj, Quinn M. Konopacky, Christopher A. Theissen et al. (+3 more)

JWST has enabled the measurement of carbon, oxygen, and sulfur abundances in the atmospheres of directly imaged planets. Interpretation of these abundances from a planet formation standpoint requires the corresponding abundances for the host star. In this work, we present detailed characterizations of the cold imaged planet hosts AF Lep A and $\epsilon$ Indi A using high-resolution Gemini/GHOST spectra. We derive the atmospheric parameters $T_{\rm eff}$ and $\log{g}$ using two different approaches, revealing differences in $T_{\rm eff}$ up to $\sim260\,$K. The derived parameters are subsequently incorporated in measurement of 16 elemental abundances (C, O, Na, Mg, Si, S, K, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Y) and several abundance ratios. Utilizing both the spectral fit and the equivalent width methods, we find solar C/O, C/S and O/S ratios ($<1.5\sigma$) for AF Lep A and $\epsilon$ Indi A. We compare our measured abundances and their ratios with those of the planets AF Lep b and $\epsilon$ Indi Ab, with the elevated abundances for the planets relative to their host stars strongly indicating formation by core-accretion pathways.
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All authors Aneesh Baburaj, Quinn M. Konopacky, Christopher A. Theissen, Jerry W. Xuan, Roman Gerasimov, Kielan K. W. Hoch

Solar and Stellar Astrophysics

Planetary systems in the light of asteroseismology: metallicity threshold for the planetary systems and age-metallicity relation

M. Y{\i}ld{\i}z, A. Demirkol, S. Örtel et al. (+2 more)

We compiled data for 127 hosts (plus six candidates) and used them as constraints to construct interior models of the hosts using the {\small MESA} code. Two significant conclusions emerge from these models. First, except for a few stars, the hosts' metallicity ($Z_0$) is greater than 0.007. This suggests a possible suppression of the occurrence of planets below $Z_0\approx0.007$. Second, it concerns how chemical evolution unfolds in the galactic disc. For a given $Z_0$ value, considering the oldest stars, there is a linear relationship between $Z_0$ and age ($t_9$). This line is around $t_9=13.4$ Gyr at $Z_0=0$, a value consistent with the age of the Galaxy. The linear relationship continues until around $t_9=6$ Gyr, and the maximum value of $Z_0$ remains constant between $t_9=2-6$ Gyr. We further modelled 12 hosts classified as red clump (RC) stars in the literature, explicitly accounting for mass loss along the red giant branch. These models highlight the critical role of mass-loss assumptions in determining the initial masses and ages of RC hosts, and their implications for the survival and evolution of close-in planets. Another key outcome of this study is the discovery of the relationship between $Z_0$ and the observed metallicity ($Z_{\rm s}$) for the hosts. We obtain a useful expression for $Z_0$, the input parameter for the models, as a function of stellar mass, radius, and $Z_{\rm s}$. This expression can be used to estimate $Z_0$ based on the reduced surface metallicity due to microscopic diffusion. We also derive an expression for planetary mass relative to the orbital semimajor axis and host mass. This expression may indicate a mass distribution near the inner disc where these planets formed, except for hot-Jupiters. Planet radii appear to depend on the planet's mass and irradiation energy, as well as the orbital period.
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All authors M. Y{\i}ld{\i}z, A. Demirkol, S. Örtel, T. Çak{\i}r Alsaç, T. Daylan

Saturday 15 August

Solar and Stellar Astrophysics

Determining low-$\ell$ p-mode frequency shifts in Sun-like stars: Enhancing the cross-correlation technique with filters

Samarth G. Kashyap, Laurent Gizon, Jesper Schou et al. (+1 more)

Acoustic mode frequencies in the Sun and Sun-like stars change due to magnetic activity, on time-scales much larger than the star's rotation and much smaller than its evolution. Given the poor S/N of the observed stellar p-modes, it is challenging to measure the changes of individual mode frequencies. Typically, power spectra of different time series segments are cross-correlated to estimate a mean p-mode frequency change, which ends up averaging over the individual mode contributions. We seek to enhance the cross-correlation method, by introducing a novel and computationally cheap method, thus enabling us to disentangle p-mode frequency changes for different spherical harmonic degree $\ell$. Assuming that the inclination angle and rotation rate are already measured, filters are designed, which enable the isolation of $\delta\omega_\ell$, frequency changes of modes with a given $\ell$, while preventing bias creeping in from neighbouring modes. Monte-Carlo simulations are performed to quantify uncertainty in the estimation of $\delta\omega_\ell$. We validate our method against well-studied solar data (SOHO/VIRGO and BiSON) and demonstrate its applicability to the solar-like Kepler star KIC 8006161.
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All authors Samarth G. Kashyap, Laurent Gizon, Jesper Schou, Rachel Howe

Solar and Stellar Astrophysics

Stability of circumbinary orbits in misaligned triple star systems

Stephen Lepp and Rebecca G. Martin

We investigate the stability of circumbinary orbits in hierarchical triple star systems, focusing on the effects of a misaligned outer companion star. Test particles are subject to competing gravitational torques from the inner binary and the outer binary companion. With secular theory we estimate the outer radius of particle stability, where the torques balance. We find good agreement with $n$-body simulations across a wide range of triple star configurations. Stable circumbinary orbits can exist even in strongly misaligned triples. Polar and highly inclined orbits with respect to the inner binary can remain stable over a substantial radial range, which is insensitive to the triple star misalignment. Orbits that are close to coplanar or retrograde coplanar to the inner binary are more susceptible to instability when the mutual inclination between the binaries is large. These findings indicate that misaligned and polar circumbinary disks and planets can survive in triple star systems under a broad set of conditions. The analytic criterion identifies where stable material may exist, with implications for the formation and detection of circumbinary planets in multiple-star systems.
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Solar and Stellar Astrophysics

A self-consistent solar coronal heating model by Alfvenic waves

Hidetaka Kuniyoshi and Richard J. Morton

Alfvenic waves are prevalent throughout the solar atmosphere and are believed to play an essential role in coronal heating, classified as alternating current (AC) heating in contrast to direct current (DC) heating associated with quasi-static magnetic field line braiding. The relative importance of AC versus DC heating depends on the details of the photospheric driver and on the configuration of the magnetic field. Moreover, even if AC heating prevails, several wave dissipation mechanisms have been proposed, and which of them dominates remains unclear, as its efficiency depends on plasma compressibility and density inhomogeneity. We address these issues by performing three-dimensional radiative magnetohydrodynamic (MHD) simulations of a coronal loop spanning from the upper convection zone to the corona, which self-consistently capture many relevant physical processes. We find that the corona is predominantly heated by AC heating, with Alfven wave turbulence providing the primary contribution, accounting for at least 80% of the entire coronal heating in the present simulation. Our results strongly support the use of Alfven wave turbulence-based models employed in space weather and stellar activity research, such as the Alfven Wave Solar Model (AWSoM) and the Magnetohydrodynamic Algorithm outside a Sphere (MAS).
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Solar and Stellar Astrophysics

Panchromatic JWST Observations and Models of the Dim Type Iax Supernova 2024vjm at 200 days

E Baron, J. M. DerKacy, C. Ashall et al. (+23 more)

We report JWST spectra and photometry of the underluminous SN Iax 2024vjm obtained 202.8 restframe days post-explosion. The spectrum exhibits a rich set of forbidden lines from low-ionization, intermediate-mass, and iron-group elements, notably the [Ni II] 6.64 micron resonance line, which is a direct indicator of stable nickel. Strong CO and SiO emission is detected alongside a warm dust continuum; the spectral properties are consistent with pre-existing rather than newly formed dust. Synthetic spectra were computed with the generalized stellar atmospheres code PHOENIX/1D using simplified ejecta models. The models reproduce the overall spectral energy distribution and the molecular emission features reasonably well, but substantially underestimate the strength of the mid-infrared atomic forbidden lines, leaving the synthetic spectrum dominated by molecular emission. Experiments in which the molecular opacity is suppressed do not recover the forbidden lines; instead, the emission peak migrates to Co and Fe transitions near 2 microns. We attribute this discrepancy to poorly constrained collisional rates and possibly to an excess of iron-group material in the current ejecta models. A prominent feature at 12.8 microns is not well accounted for by the [Ne II] 12.81 micron line, indicating that the 12.8 micron feature may be largely due to [Fe III]. The presence of CO, SiO, and stable nickel together with the non-detection of neon places tight constraints on the total ejecta mass and the nucleosynthetic yields of SNe Iax progenitor systems.
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All authors E Baron, J. M. DerKacy, C. Ashall, M. Shahbandeh, Peter H. Hauschildt, T. Barman, J. P. Aufdenberg, C. R. Burns, N. Morrell, M. D. Stritzinger, P. Hoeflich, K. Medler, E. Fereidouni, C. M. Pfeffer, T. Mera, W. B. Hoogendam, S. Shiber, P. J. Brown, Divya Mishra, Inma Dominguez, L. Galbany, Paolo Mazzali, E. Y. Hsiao, Huangfei Xiao, T. de Jaeger, S. Kumar

Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

Detection of Aliphatically Deuterated Aromatic Hydrocarbons in the Large Magellanic Cloud 30 Doradus Star-Forming Complex

Junhao Peng, Xuejuan Yang and Aigen Li

The unidentified infrared (IR) emission (UIE) bands at 3.3, 6.2, 7.7, 8.6, 11.3 and 12.7 micron are ubiquitously seen in a wide variety of astrophysical environments. While the exact assignment of these UIE bands remains controversial, they are generally ascribed to C–H and C–C stretching and bending vibrations of aromatic hydrocarbon molecules. Here, based on observations made with the Near Infrared Spectrograph (NIRSpec) and the Mid Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST), we report that the UIE emitters in the 30 Doradus star-forming complex in the Large Magellanic Cloud (LMC) are deuterated and have an appreciable amount of aliphatic content. The spatially resolved NIRSpec and MIRI spectra of 30 Doradus reveal a widespread detection of the 3.4 and 6.85 micron emission features attributed to aliphatic C–H stretch and deformation, respectively, as well as the 4.65 micron feature attributed to aliphatic C–D stretch. Notably, the 6.85 micron feature exhibits three complex substructures at ~6.83, 6.86 and 6.88 micron that have never been reported before.
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Friday 14 August

Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

Local Interstellar Flow Parameters from the First Intersection of IMAP-Lo's Parameter Tubes

Nathan A. Schwadron, Mitchell M. Shen, Fatemeh Rahmanifard et al. (+24 more)

The Sun's motion through the interstellar medium creates a flow of interstellar neutral (ISN) atoms through the heliosphere. ISN He, due to its high universal abundance and relatively low ionization rate, is the most abundant of the interstellar species near 1 au and ideal for flow parameter determination. The Interstellar Boundary Explorer (IBEX) measurements of ISN He flow parameters (speed, temperature, and direction) yielded a tube in 4D parameter space – narrow in cross-section but highly extended along one parameter axis (e.g., ecliptic longitude direction). This “4D parameter tube” results in large systematic uncertainties, a direct consequence of IBEX-Lo's fixed viewing orientation on the spacecraft. On the Interstellar Mapping and Acceleration Probe (IMAP), the articulation of the IMAP-Lo boresight using its pivot platform enables multiple viewing orientations of the ISN flow for significant systematic uncertainty reduction. We provide first results that definitively intersect ISN parameter tubes for elongation angles $79^\circ$, 94$^\circ$, and 109$^\circ$, resulting in precise interstellar parameters: speed $26.37 \pm 0.82$ km s$^{-1}$, ecliptic longitude direction $74.85^\circ \pm 0.96^\circ$, ecliptic latitude direction $-5.212^\circ \pm 0.035^\circ$, and temperature $7740^{+770}_{-730}$ K. The inferred flow of the Very Local Interstellar Medium is not consistent with either the Local Interstellar Cloud or the G-Cloud, but rather an intermediate state. IMAP is now positioned to study the detailed physics of this complex, nearby interstellar region. By resolving and understanding its physics, we determine how the heliosphere responds to the local interstellar flow, and how it may evolve in time
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All authors Nathan A. Schwadron, Mitchell M. Shen, Fatemeh Rahmanifard, Eberhard Moebius, Hafijul Islam, Jonathan S. Bower, Maciej Bzowski, Eric R. Christian, Ken Fairchild, Herbert O. Funsten, Stephen A. Fuselier, Andre Galli, Jonathan Gasser, Matina Gkioulidou, David Heirtzler, Izabela Kowalska-Leszczyska, Marzena A. Kubiak, David J. McComas, Jonathan T. Niehof, Jamie S. Rankin, Justyna Sokol, Pawel Swaczyna, Jamey R. Szalay, Carol Weaver, Peter Wurz, Gary P. Zank, Eric J. Zirnstein

Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

Mixing stochasticity relinquishes evidence for magnetorotational hypernovae

Anmol Aggarwal and Ralph Schoenrich

A recent work claimed by fitting the observed elemental abundance pattern of a halo star with the total yields from single super-/hypernova events that only a magnetorotational hypernova event (a very energetic supernova event that also produces r-process elements) could be the source of the observed abundances. Here, we show that the star's peculiar abundance pattern is better fitted within the framework of mixing stochasticity with yields from a normal core collapse supernova (ccSN; Energy$_{\rm exp}$ $\sim 10^{51}$ erg.) and a neutron star merger (NSM). The stochastic mixing model outperforms the hypernova fitting significantly, (r.m.s 0.24 vs 0.44) i.e., favours the composition from common events (ccSN + NSM) over the magnetorotational hypernova scenario. We also discuss the origin of the star and the possibility of enrichment of its birth cloud by both a ccSN and a NSM.
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Solar and Stellar Astrophysics

JWST/NIRSpec Spectra for Three Ultracool Brown Dwarfs Detected in Extragalactic Surveys: Further Evidence for Phosphine Absorption

Kevin N. Hainline, Samuel A. Beiler, Adam J. Burgasser et al. (+14 more)

We present JWST NIRSpec prism spectra for three ultracool brown dwarfs discovered in extragalactic survey data, two from the JWST Advanced Deep Extragalactic Survey (JADES), and one from Public Release IMaging for Extragalactic Research (PRIMER) survey observed as part of the Mirage or Miracle (MoM) program. The spectra for these sources indicate that one is a T6 dwarf (JADES-GS-BD-11, T$_{\mathrm{eff}} = \sim 700$ K) and two are Y0-Y1 dwarfs (JADES-GS-BD-5, T$_{\mathrm{eff}} = \sim 400$ K, and MoM-239450, T$_{\mathrm{eff}} = \sim 500$ K). Model atmospheric fits with $\texttt{NIFTY}$ to the spectra are consistent with this classification, and indicate that JADES-GS-BD-5 is only $\sim 150$ pc from the Sun, MoM-239450 is $\sim 700 - 800$ pc from the Sun, and JADES-GS-BD-11 is $\sim 1$ kpc from the Sun, with these latter two more distant sources being best fit at sub-solar metallicities. JADES-GS-BD-5 has an observed spectrum with significantly weaker J and H band emission than Y dwarf atmospheric models, potentially indicating the presence of water ice clouds in the brown dwarf. The spectrum for JADES-GS-BD-11 has a feature at 4.3$\mu$m consistent with absorption from the rarely seen phosphine molecule at $2.6\sigma$ confidence. Given the low metallicity for this source ([M/H] $ = -0.7$), our finding supports the theory that detecting phosphine in brown dwarf atmospheres is tied to atmospheric metallicity. JWST/NIRSpec spectroscopy continues to be a powerful tool for understanding the properties of these distant, and very cold brown dwarfs.
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All authors Kevin N. Hainline, Samuel A. Beiler, Adam J. Burgasser, Evan S. Chen, Jakob M. Helton, Jarron Leisenring, Brittany E. Miles, Mark S. Marley, Sagnick Mukherjee, Stefi Baum, Andrew J. Bunker, Stefano Carniani, Francesco D'Eugenio, Eiichi Egami, Tobias J. Looser, Pierluigi Rinaldi, Christopher N. A. Willmer

Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

The Galactic Centre G+0.633-0.0604 Molecular Cloud: A New Gold Mine for Astrochemistry

D. San Andrés, V. M. Rivilla, L. Colzi et al. (+4 more)

Astrochemistry is living a golden age, with more than a quarter of the ~350 molecules in the current interstellar census having been detected over the last three years. One of the sources driving this progress is the G+0.693-0.027 cloud, located in the northern part of the Galactic Centre Sgr B2 complex. In this contribution, we present the astrochemical characterisation of G+0.633-0.0604, a newly discovered chemically rich molecular cloud at the southern edge of Sgr B2. With an inventory of >120 species, G+0.633 provides robust second detections of several prebiotic molecules only reported towards G+0.693, establishing it as the first confirmed astrochemical twin of G+0.693 while demonstrating that the extraordinary chemistry of this cloud is not unique. Furthermore, G+0.633 offers an observational advantage over G+0.693 since it displays half narrower linewidths. Together, G+0.633 and G+0.693 form a unique benchmark pair for unveiling molecular complexity and prebiotic chemistry in the interstellar medium.
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All authors D. San Andrés, V. M. Rivilla, L. Colzi, M. Sanz-Novo, S. Martín, I. Jiménez-Serra, S. Zeng

Solar and Stellar Astrophysics

Magnetoacoustic Portals in Quiet-Sun Fluxtubes Revealed by Chromospheric Spectropolarimetry with SUNRISE III/SCIP

Takayoshi Oba, Yukio Katsukawa, Masahito Kubo et al. (+36 more)

Acoustic waves propagate into the chromosphere, contributing to energy transport and their dynamics. Their upward propagation is restricted to frequencies above the acoustic cutoff frequency. The magnetic field configuration plays a key role in determining whether acoustic waves can propagate upward because the cutoff frequency is reduced in regions where the field is inclined with respect to gravity, forming so-called magnetoacoustic portals. Previous studies linked magnetic fields and oscillations in quiet regions, but these analyses were based on photospheric magnetic field information, leaving chromospheric structure unconstrained. This study investigates the coupling between acoustic waves and magnetic topology using photospheric and, for the first time, chromospheric spectropolarimetry in a quiet region, obtained with the Sunrise Chromospheric Infrared SpectroPolarimeter (SCIP) aboard the Sunrise iii balloon-borne solar observatory launched in 2024. The SCIP sit-and-stare observations sampled magnetic features in which the line-of-sight field strength exhibits multiple sharp spatial peaks in the photosphere while becoming broader and weaker at two heights in the chromosphere, indicating expanding fluxtubes. The chromospheric velocity field in these fluxtubes exhibits strong 5-minute oscillations, while the surrounding regions show weak 3-minute oscillations. In these fluxtubes, sawtooth temporal velocity variations are associated with intensity enhancements, suggesting steepened shocks. Fluxtubes with low-frequency oscillations are identified not only in network regions but also in weak internetwork regions. These results provide observational evidence that fluxtubes expanding into the chromosphere act as magnetoacoustic portals, in both network and internetwork regions, allowing low-frequency waves to propagate upward and driving chromospheric dynamics via shocks.
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All authors Takayoshi Oba, Yukio Katsukawa, Masahito Kubo, Yusuke Kawabata, Takuma Matsumoto, Ryohtaroh T. Ishikawa, Yoshihiro Naito, Toshifumi Shimizu, Hirohisa Hara, Fumihiro Uraguchi, Toshihiro Tsuzuki, Kazuya Shinoda, Tomonori Tamura, Yoshinori Suematsu, Jose Carlos del Toro Iniesta, David Orozco Suárez, Maria Balaguer Jiménez, Azaymi L. Siu-Tapia, Carlos Quintero Noda, Sami K. Solanki, Andreas Lagg, Achim Gandorfer, Pietro Bernasconi, Thomas Berkefeld, Tino L. Riethmüller, Alberto Álvarez-Herrero, H. N. Smitha, Bianca Grauf, Michael Carpenter, Alexander Bell, Valentín Martínez Pillet, Francisco Javier Bailén, Julian Blanco Rodríguez, Juan Sebastián Castellanos Durán, Edvarda Harnes, Johannes Hölken, Francisco A. Iglesias, Hanna Strecker, Dušan Vukadinović

Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph

Physics of Circular Polarized Ion-Scale Waves in Hybrid Simulations of Alfvénic Fluctuations

Hai Yang Harry Qian, Trevor A. Bowen, Carlos A. Gonzalez et al. (+5 more)

Ion cyclotron waves (ICW) and fast magnetosonic/whistler waves (FMW) are fundamental electromagnetic modes at ion kinetic scales, yet their generation mechanisms and roles in plasma evolution remain poorly understood. We analyze a 2.5D hybrid simulation of broadband Alfvénic fluctuations, where the proton velocity distribution is modeled as a sum of two bi-Maxwellian components: a thermal core and a drifting beam. Using wavelet-based wave identification, bi-Maxwellian VDF fitting, and the PLUME linear dispersion solver, we find that ICW behave as linear modes. Growth is intermittent, occurring when core temperature anisotropy builds up, and is driven mainly by the core (the beam contributes negligibly). Poynting flux analysis shows that ICW are predominantly forward-propagating, with a net energy flux ratio of $+1$ across all frequencies, consistent with the initial condition. FMW present a stark contrast: PLUME solutions often yield very small (near-zero) linear growth/damping rates. The species decomposition breaks down when $|\gamma/\omega_r| \gtrsim 0.368$, indicating that linear theory predicts these waves to be strongly damped and not describable by linear eigenmodes. Nevertheless, FMW are clearly observed in the wavelet helicity spectrogram, indicating that they are generated by nonlinear processes (e.g., parametric decay or phase steepening) and persist despite linear damping. The net energy flux ratio for FMW is close to $+1$ at low frequencies but decreases at higher frequencies, yet never reaches zero (net energy flow remains forward). These results demonstrate that ICW are linear, core-driven waves that transfer energy to the plasma, while FMW are heavily damped, nonlinearly generated waves.
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All authors Hai Yang Harry Qian, Trevor A. Bowen, Carlos A. Gonzalez, Nikos Sioulas, Alfred Mallet, Kristopher G. Klein, Daniel Verscharen, Stuart D. Bale

Solar and Stellar Astrophysics

The B-Index as a Diagnostic of Cool Stars: Assessing Metallicity Dependence of TiO Absorption in the Visible Spectrum

Fatemeh Azizi, Mohammad Taghi Mirtorabi and Zahra Mohammadian

Molecular absorption features constitute essential diagnostics of late-type stellar atmospheres, with titanium oxide (TiO) bands serving as sensitive tracers of effective temperature and magnetic activity. While near-infrared TiO indices are well established, visible-band diagnostics provide complementary constraints for stellar classification and parameter estimation. This study investigates the metallicity dependence of the B-index, a TiO absorption measure centered at 567 nm, through synthetic spectra generated with ATLAS9 and high-resolution observations from the HARPS spectrograph. The synthetic grid spans effective temperatures between 3500-4000 K and metallicities from [Fe/H] =-4 to +0.2, while the observational sample comprises 23 MK spectral types stars with effective temperatures between 3500-4000 K. Both theoretical and empirical analyses demonstrate that the B-index exhibits negligible sensitivity to stellar metallicity, with only marginal correlations detected. Therefore, there is no requirement to include this feature in the calculation of the B-index. The B-index's low sensitivity to metallicity reinforces its utility as an effective tool for spectral classification, stellar atmosphere modeling, and the study of magnetically active stars.
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Solar and Stellar Astrophysics

High-order Paschen emission from the quiet-Sun off-limb chromosphere

Haocheng Yu, Yukio Katsukawa, Mingde Ding et al. (+31 more)

We report the detection of high-order hydrogen Paschen emission lines (Pa~15, Pa~16, and Pa~17) in the quiet-Sun chromosphere off the solar limb using the Chromospheric Infrared SpectroPolarimeter (SCIP) on board the Sunrise~iii balloon telescope. These lines reveal thread-like structures resembling spicules and exhibit systematically smaller Doppler velocities than Ca~II~854.2~nm, suggesting that they are optically thinner and more affected by line-of-sight averaging, especially near the limb. Non-LTE radiative transfer synthesis using the spherically symmetric one-dimensional code rhsphere reproduces the overall spectral properties. The observed ratios among three Paschen lines show systematic deviations from synthetic and theoretical results, suggesting that additional physical effects may influence the formation of high-order Paschen lines. The study demonstrates the potential of high-order Paschen lines as a new diagnostic of optically thin plasma in the off-limb chromosphere.
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All authors Haocheng Yu, Yukio Katsukawa, Mingde Ding, Takuma Matsumoto, Sami K. Solanki, Julian Blanco Rodríguez, David Orozco Suárez, Masahito Kubo, Andreas Lagg, Achim Gandorfer, José Carlos del Toro Iniesta, Pietro Bernasconi, Thomas Berkefeld, Alex Feller, Tino L. Riethmüller, Alberto Álvarez-Herrero, H. N. Smitha, Bianca Grauf, Michael Carpenter, Alexander Bell, Valentín Martínez Pillet, Francisco Javier Bailén, Juan Sebastián Castellanos Durán, Edvarda Harnes, Johannes Hölken, Francisco A. Iglesias, Ryohtaroh T. Ishikawa, Yusuke Kawabata, Takayoshi Oba, Azaymi L. Siu-Tapia, Hanna Strecker, Dušan Vukadinović, Hirohisa Hara, Toshifumi Shimizu

Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

X-ray Activity of the RS CVn-type Star {\sigma} Gem with the First-Year Observations of Einstein Probe

Xuan Mao, Giuseppina Micela, Fabio Favata et al. (+3 more)

Context. Stellar flares are energetic events driven by the sudden release of magnetic energy in the stellar atmosphere. Studying these flares is crucial for understanding their impact on exoplanets, the circumstellar environment, and stellar evolution itself. The launch of the Einstein Probe (EP) offers a unique opportunity to systematically detect such events. Aims. We present a systematic analysis of the flaring activity of the active RS CVn-type binary {\sigma} Gem, utilizing the first-year monitoring data from the Wide-field X-ray Telescope (WXT) aboard EP. Our goals are to demonstrate the unique capability of EP in monitoring stellar X-ray activity and detecting flares, by identifying and characterizing extreme X-ray flares on {\sigma} Gem and estimating their occurrence rate. Methods. We developed a data-processing pipeline to select and extract EP-WXT observations, producing a background-subtracted, vignetting-corrected light curve. We employed the Bayesian Blocks method to detect significant flares in the long-term X-ray light curve. For each identified flare, we performed light curve and spectral fitting to derive the flare parameters. Results. Between October 2024 and April 2025, WXT detected 6 distinct flares from {\sigma} Gem. Their durations ranged from 21 hours to 3 days, with peak X-ray luminosities (0.5-4 keV) of 3.7 * 10^31 to 7.0 * 10^32 erg/s and total energies of 1.1 * 10^36 to 4.4 * 10^37 erg, placing them among the "superflare" class. Conclusions. Using {\sigma} Gem as a case study, we demonstrate an analysis process for flare detection and analysis with EP-WXT data, which provides new statistical constraints on its flaring behavior. Applying this methodology to the growing EP stellar archive promises to yield a vast sample of X-ray flares, which will significantly advance our understanding of stellar magnetic activity.
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All authors Xuan Mao, Giuseppina Micela, Fabio Favata, Weimin Yuan, He-yang Liu, Huaqing Cheng

Solar and Stellar Astrophysics

Evidence for Dynamical Filtering: High Binary Fraction, Hard-binary Excess, and Unresolved Triples in the Surviving Core of NGC 6791

Huanbin Chi, Zhi Li, Feng Wang et al. (+4 more)

We present a deep photometric analysis of the main-sequence (MS) population in the old, metal-rich open cluster (OC) NGC 6791 using Gaia Data Release 3 data. After correcting for differential reddening, we use the Bayesian model comparison to test whether stellar rotation can account for the observed MS broadening and find that a rotation-dominated interpretation is strongly disfavored. We therefore infer that unresolved multiplicity is the primary contributor to the photometric offsets. We derive a high-q companion fraction of $54.3\% \pm 2.8\%$ for systems with $q \gtrsim 0.5$, significantly higher than typical values reported for most OCs and the field. The inferred offset distribution is not consistent with a flat mass-ratio distribution but instead shows an excess toward high mass ratios ($q \sim 0.8$–$1.0$), suggestive of preferential survival of hard binaries in a dynamically evolved environment. We also identify a population of stars lying above the equal-mass binary limit ($\Delta G > 0.75$ mag), which is difficult to explain with ordinary MS binaries alone and is plausibly interpreted as candidate unresolved triple or higher-order multiple systems. A Kolmogorov–Smirnov test, together with Monte Carlo label-shuffling experiments, shows no statistically significant difference between the projected radial distributions of the single-star and binary/multiple populations within the observed field. Taken together, these results are consistent with the picture that NGC 6791 is the dynamically processed inner remnant of a once more massive cluster.
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All authors Huanbin Chi, Zhi Li, Feng Wang, Xuefen Tian, Linfeng Chang, Hongbo Liu, Yiqin Liu

Solar and Stellar Astrophysics

A chemo-dynamical search for planet-candidate hosts of possible extragalactic origin

Sun Tiancheng, Chen Xunzhou, Xiang Maosheng et al. (+2 more)

To date, all known exoplanetary systems have been identified around stars currently residing in the Milky Way, whereas planets formed in external galaxies remain largely unexplored. Such systems would offer a unique probe of planet formation in galactic environments distinct from the Milky Way. We combine a literature-compiled sample of Kepler, K2, and TESS planet-candidate host stars with Gaia DR3 astrometry and radial velocities, and incorporate metallicities and [Mg/Fe] abundances from the LAMOST DR9 DD-Payne catalogue, to search for candidate accreted-halo planet hosts. We identify 11 planet-candidate hosts with halo-like kinematics, five of which have reliable chemical abundance measurements. Among these, four systems exhibit low metallicities ([Fe/H]<-0.7) and low [Mg/Fe] ratios that are inconsistent with the canonical Milky Way thick-disc sequence, indicative of enrichment histories characteristic of accreted dwarf galaxies. We further carry out a uniform false-positive assessment using Gaia RUWE, Gaia DR3 neighbourhood checks, odd–even transit-depth comparisons, secondary-eclipse searches, independent BLS period recovery, and comparison with ExoFOP and available follow-up information. This vetting identifies EPIC~211407755 and TIC~239541449 as the most plausible, although still unvalidated, planet-candidate systems. TIC~293432942 is more likely associated with a blended or otherwise binary-related false positive, whereas TIC~184739529 remains a high-risk giant-companion candidate whose planetary nature is uncertain. If confirmed, EPIC~211407755 and TIC~239541449 would suggest that planetary systems can form in dwarf-galaxy environments and subsequently survive accretion into the Milky Way.
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All authors Sun Tiancheng, Chen Xunzhou, Xiang Maosheng, Zhou Jianzhao, Lu Zixuan

Thursday 13 August

Solar and Stellar Astrophysics

H-$\alpha$ Integral Carrington Synoptic Maps Produced by NSO/NISP

K. J. Shuman, L. Bertello, O. Burtseva et al. (+1 more)

Monitoring long-term chromospheric activity and large-scale solar structures like filaments and plages is critical for understanding solar magnetic cycles and predicting space-weather events. While photospheric magnetic fields are routinely mapped, a consistent, global reference for chromospheric structures has been absent from H-$\alpha$ observations. This technical report provides a comprehensive description of the methodology used to construct the NSF Global Oscillations Network Group (GONG) H-$\alpha$ Integral Carrington Synoptic Maps from full-disk observations. We outline the processing pipeline developed to transform these observations into 720 x 360 pixel maps binned by Carrington longitude and sine(latitude) and describe characteristics of the final data product.
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All authors K. J. Shuman, L. Bertello, O. Burtseva, A. A. Pevtsov

Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

No Evidence for Nearby Circumstellar Material in the Type Ia Supernova 2025rbs

Aravind P. Ravi, Griffin Hosseinzadeh, Stefano Valenti et al. (+28 more)

We present a high-resolution spectral time series of the Type Ia supernova (SN) 2025rbs discovered in the nearby galaxy NGC 7331. The Automated Planet Finder (APF) at Lick Observatory and the MAROON-X/IGRINS-2 at Gemini North were used to obtain echelle spectra between -5 and 15 days with respect to the epoch of maximum light. Several unsaturated NaID absorption components along the line of sight are identified, but there is no evidence of time variance in any of them. We measure the equivalent width of the observed diffuse interstellar band around 5780 A and constrain the extinction along the line of sight to SN 2025rbs as $A_V = 0.64\,\pm\,0.32$ mag, corresponding to a moderate reddening of $E(B-V) = 0.21\,\pm\,0.10$ mag (assuming $R_\mathrm{V}$ = 3.1). The observed Ca II H & K interstellar absorption roughly traces NaID in velocity space, suggesting a common origin. Quantitative comparisons between the column densities of Na and Ca gas in these host clouds ($N_{NaID}$ / $N_{Ca II}$ of order unity) argue against their origin in the Galactic halo gas and instead support absorption due to the interstellar gas of NGC 7331. Time invariance of all the observed absorption features suggests a lack of nearby circumstellar material ($\lesssim$ 10$^{16}$ cm) around the progenitor system of SN 2025rbs. This supports a progenitor scenario for SN 2025rbs with minimal ambient circumstellar gas, consistent with a double-degenerate CO white dwarf binary system.
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All authors Aravind P. Ravi, Griffin Hosseinzadeh, Stefano Valenti, Saurabh W. Jha, Jennifer Andrews, David J. Sand, Benjamin J. Fulton, William D. Vacca, Melissa L. Graham, Alexei V. Filippenko, Noah Franz, Jeniveve Pearson, Moira Andrews, K. Azalee Bostroem, Collin Christy, Yize Dong, Sebastian Gomez, Daichi Hiramatsu, Emily Hoang, D. Andrew Howell, Brian Hsu, Daryl Janzen, Lindsey A. Kwok, Michael J. Lundquist, Darshana Mehta, Nicolas Meza-Retamal, Curtis McCully, Manisha Shrestha, Bhagya Subrayan, Lauren Weiss, Weikang Zheng

Solar and Stellar Astrophysics

Radio Properties of RS Canum Venaticorum Variables in VLASS and RACS

Suhasini S. Rao, Gregory R. Sivakoff, Craig O. Heinke et al. (+6 more)

We performed a systematic search for radio emission from RS Canum Venaticorum (RS CVn) binaries, selected from the International Variable Star Index (VSX) catalog, in the Very Large Array Sky Survey (VLASS; three epochs) and Rapid ASKAP Continuum Survey (RACS; two epochs) data. We detected 108 candidate radio-emitting RS CVn in at least one epoch. Several of these systems rank among the most radio-luminous RS CVn binaries reported to date. The radio and X-ray luminosities, obtained from cross-matching with the eROSITA and ROSAT X-ray catalogs, are consistent with the Guedel-Benz relation for magnetically active stars, but are also comparable to radio-luminous quiescent black hole X-ray binaries, indicating a potential for misidentification between these two classes. Analysis of optical, radio, and stellar properties indicates that optically bright RS CVn (i.e., those with at least one giant component) are radio-quieter and have periods that are consistent with lower coronal activity. However, two of these optically bright RS CVn systems show persistent and unusually high radio specific luminosities (>2e17 erg/s/Hz) across all observed epochs, showing that stellar activity can produce relatively persistent radio signals as bright as quiescent black hole binaries.
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All authors Suhasini S. Rao, Gregory R. Sivakoff, Craig O. Heinke, Swetha Arumugam, Dougal Dobie, Laura Driessen, David L. Kaplan, Emil Lenc, Joshua Pritchard

Solar and Stellar Astrophysics · Cross-listed from physics.hist-ph

From the Earth to the Sun

Dieynaba Young

This year marks 360 years since the founding of the French Academy of Sciences. This is the story of the academy's daring 17th century expedition to measure the Earth-sun distance. A truncated version first appeared in National Geographic Magazine; the following is closer to the original draft, with updated information and references.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

The sensitivity of TESS to transiting planets in TOIs with close-in stellar companions

Colin Littlefield, Kathryn V. Lester, David R. Ciardi et al. (+1 more)

High resolution imaging with optical speckle interferometry has revealed that many transiting exoplanet host stars possess close-in stellar companions. The objective of this study is to quantify how the presence of these companions impacts the ability of TESS to detect the transits of small planets. We accomplish this by examining 2052 TESS Objects of Interest (TOIs) that appear to be single-star systems based on speckle interferometric observations as well as 188 TOIs in unresolved ($< 1.2\arcsec$) stellar binaries. For each planet, we take its transit signal-to-noise ratio (SNR), radius, and orbital period from the TOI catalog and, for planets in stellar binaries, we correct the radius for dilution by the companion. By applying a scaling relation to the measured transit SNR of each TOI in our sample, we determine the detectability of transits in each TOI as a function of both planet radius and orbital period. When applied to the full sample, this procedure elucidates the sensitivity of TESS to transiting planets as a function of binarity, host-star spectral type, planet radius, and planet orbital period. These sensitivity grids quantify the bias against the detection of small planets in unresolved binaries by TESS and show that there is a particularly low sensitivity to planets transiting secondary stars in unresolved binaries, especially as the magnitude difference between the stars increases. These sensitivity grids are available for download to facilitate their use in other studies.
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All authors Colin Littlefield, Kathryn V. Lester, David R. Ciardi, Steve B. Howell

Solar and Stellar Astrophysics

The Production of Electron-Capture Elements in Thermonuclear Supernovae: Theory vs. Observations

S. Shiber, P. Hoeflich, T. Mera et al. (+9 more)

Type Ia supernovae (SNe Ia) explosively destroy carbon-oxygen white dwarfs (WDs) in multiple stellar systems. They produce approximately 50% of the iron-group elements in the Universe, synthesize electron-capture (EC) elements, drive nuclear physics experiments, and underpin high-precision cosmology. To first order, the outcome is governed by nuclear physics, a property often described as stellar amnesia. Recently, this stellar amnesia has begun to be broken by the nearly universal detection of EC elements with JWST. These elements trace high-density burning, largely ruling out the currently popular helium-triggered, sub-Mch detonation models as the dominant channel. Instead, the ubiquitous presence of EC is shifting back the focus to dynamical and secular mergers, and near-Mch explosions similar to the deflagration model W7, but in which the nuclear flame undergoes a deflagration-to-detonation transition. The early deflagration phase is especially important because spherical simulations identify the central WD density, and thus the WD mass, as a key parameter governing the explosion. Here, we present detailed magneto-hydrodynamical simulations. We find that small-scale, pre-existing turbulence expected from the pre-explosion smoldering phase is essential for overcoming the fundamental challenges imposed by the intrinsic 3D physics. This turbulence systematically reduces the production of EC elements by about a factor of two, implying the need for WD central densities closer to those associated with accretion-induced collapse to a neutron star. We also demonstrate the effect of magnetic fields near the saturation field strength and highlight the need for higher-precision EC rates at low Ye.
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All authors S. Shiber, P. Hoeflich, T. Mera, E. Fereidouni, Z. Levy, D. Maci, C. Ashall, K. Medler, J. M. DerKacy, E. Baron, M. Shahbandeh, C. M. Pfeffer

Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE

Radio Monitoring of Classical Novae using the ASKAP Variable and Slow Transients Survey

Aishani Majumder, David L. Kaplan, Laura N. Driessen et al. (+3 more)

We present a search for radio emission from classical novae at 887.5 MHz using data from the Australian SKA Pathfinder Variable And Slow Transient (VAST) survey. We cross-matched 43 optically discovered classical novae that erupted between 2021 September and 2025 November within the 1200-square-degree Galactic survey footprint, and found three which show significant radio emission: V6598 Sgr, V1716 Sco, and V1723 Sco. To analyse their radio light curves, we use both thermal free-free and non-thermal synchrotron emission models. We fit the data using the Markov chain Monte Carlo (MCMC) method to constrain parameters, including the ejected mass and ejecta velocities for the thermal models, and mass-loss rate, explosion energy, wind velocity, and filling factor for the non-thermal model. All three novae show evidence of non-thermal synchrotron emission as the dominant emission mechanism at this frequency. We use a broken power law to describe the radial density structure of a non-uniform circumbinary material, which provides a better fit than a standard wind density profile. This strong early-time synchrotron emission is strong evidence of shock-driven particle acceleration, which may be related to detections of gamma-rays from all three novae as well. In contrast to earlier studies that used multi-frequency data to distinguish between emission models, our analysis is based on single-frequency radio light curves, which can still provide useful constraints on the dominant emission mechanism when interpreted with physically motivated models
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All authors Aishani Majumder, David L. Kaplan, Laura N. Driessen, Ashna Gulati, Tara Murphy, Dougal Dobie

Solar and Stellar Astrophysics

JWST Detects a Dusty AGB-like Source Before the Type Ia-CSM Supernova 2026sqf

Tamás Szalai, Dan Milisavljevic, Noah Zimmer et al. (+22 more)

Supernova (SN) 2026sqf recently appeared in the nearby face-on spiral galaxy NGC 3310 and has shown signs of strong interaction with a circumstellar medium (CSM). Such intense interaction, rare among nearby SNe, offers a valuable opportunity to reveal details on the origin and nature of its progenitor system. We analyzed the early-phase spectra and light curves (LCs) of SN 2026sqf. The general shapes of the observed spectra, the strengths of the emission lines, and the LC evolution all suggest that SN 2026sqf belongs to the rare SN Ia-CSM subclass. If confirmed, this would be the closest known member of this class, at D~19 Mpc. We also report the first candidate progenitor system for a thermonuclear supernova identified in JWST pre-explosion imaging, and the first evidence for a (probable) carbon-rich AGB donor to the exploding white dwarf (WD). Our results are consistent with the expectation that SNe Ia-CSM emerge from a system consisting of a WD and an AGB star undergoing a common-envelope phase. The CSM mass and dust content are consistent with expectations for an AGB environment, but the narrow-line width exceeds superwind expansion velocities, favoring an episodic ejection. Binary interaction shortly before the explosion is a natural explanation, though the channel and timescale remain uncertain. Late-time follow-up, especially with JWST, will test the identification and the conclusions of our early-phase analysis.
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All authors Tamás Szalai, Dan Milisavljevic, Noah Zimmer, Braden Garretson, Thomas Moore, Schuyler D. Van Dyk, Anan Lu, Selcuk Topal, Ori D. Fox, Tuomas Kangas, Seppo Mattila, Andrea Reguitti, Uliana Pylypenko, Chuck Cynamon, Ting-Wan Chen, Amar Aryan, Dylan Caudill, Danielle Dickinson, Martin Bureau, Woorak Choi, Timothy A. Davis, Daryl Haggard, Thomas M. Reynolds, Maximilian Stritzinger, Patrick Wiggins

Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA

Differential Reddening and Extinction Law Analyses of Galactic Open Clusters

Xiaohan Chen, Shu Wang and Xiaodian Chen

Extinction significantly affects open cluster parameters and their use in studies of Galactic structure, yet homogeneous large sample measurements of open cluster extinction properties remain limited. Using Gaia-era open cluster member samples combined with multi-band photometry and stellar parameters, we derive color excesses of member stars and provide the homogeneous characterization of the mean reddening, differential reddening, and color excess ratio (CER) at the cluster scale. Differential reddening increases systematically with mean reddening, with highly reddened clusters near the Galactic plane showing stronger extinction variations. Star-by-star reddening corrections narrow color–magnitude diagram (CMD) sequences in 369 of 435 clusters (85%) with reliable CMD-width measurements, and cluster color excess maps reveal small-scale extinction structures. The median CER is compatible with the standard diffuse interstellar medium extinction curve, while the broad CER distribution and its large-scale variations across the Galactic disk likely reflect differences in the dominant dust environments sampled along different Galactic sight lines.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

Stellar tidal systematics in apsidal-motion searches for circumbinary planets: CH Ind and SW CMa

Qunfeng Jiang

Thornton et al. (2026) reported 27 non-transiting circumbinary-planet candidates from excess apsidal motion in TESS eclipsing-binary timings. The classical stellar contribution is sensitive to target-specific radii, apsidal constants $k_2$, and rotation. We re-evaluate two evolved, double-lined eclipsing binaries in that sample: the pulsating system CH Ind and the Am system SW CMa. Their component masses and radii have been measured in dedicated binary studies, allowing the stellar contribution to be calculated directly. For CH Ind, six independent TESS sector nodes give $\dot{\omega}_{\rm obs}=1.82^{+0.99}_{-0.94}\times10^{-3}\ {\rm deg\,cycle^{-1}}$, while a coeval fit to the measured binary components predicts $\dot{\omega}_{\rm stars}=2.05^{+0.43}_{-0.34}\times10^{-3}\ {\rm deg\,cycle^{-1}}$. For SW CMa, its measured dimensions raise the classical term by a factor of about 16; the published target-specific prediction, $0.670\pm0.020\times10^{-3}\ {\rm deg\,cycle^{-1}}$, agrees with the observed $0.690\pm0.050\times10^{-3}\ {\rm deg\,cycle^{-1}}$. Neither system shows a significant excess prograde component. The comparison shows that candidates from a bulk search require target-specific binary models before a third-body interpretation is assigned.
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Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP

Revisiting gravitational instability in protostellar discs with improved radiative cooling models

Alison K. Young, Ken Rice, Richard Booth et al. (+1 more)

Young discs are expected to be significantly more massive than those observed at $>1$ Myr and it is at this earliest stage that planet formation likely begins. Such massive discs may be susceptible to the gravitational instability (GI), therefore we need to determine the disc and stellar properties for which the GI is active to understand its role in early disc evolution and planet formation. Prior work has been limited by model assumptions and inaccuracies due to the complex nature of the thermodynamics of protostellar discs so we now revisit this question using an improved method to approximate radiative cooling within hydrodynamics simulations. We have explored a wide parameter space, representative of young protostellar discs of 0.1 to 1 M$_{\odot}$ and include irradiation from the host star. The parameters for which discs form spirals and fragment were found to differ to those obtained from earlier simulations. The outer regions of discs with radii of 50 au may be susceptible to fragmentation, meaning that GI-driven planet formation is not restricted to only the most extended discs. The additional thermal support due to stellar irradiation increases the disc mass that remains stable against GI: discs may reach up to $\gtrsim 0.4$ M$_*$ without fragmenting, providing a considerable quantity of material for building planets. Large scale spiral arms only developed for $M_*\lesssim$ 0.3 M$_{\odot}$, except in the most compact discs. Furthermore, the long-lived spiral structures that form tend to be flocculent and compact, indicating that large-scale spiral arms should not be considered a typical outcome of GI.
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All authors Alison K. Young, Ken Rice, Richard Booth, Farzana Meru