Thüringer Landessternwarte Tautenburg

Solar flares are complex phenomena driven by the release of magnetic energy, but a large energy reservoir is not sufficient to determine their eruptive potential; the magnetic topology and plasma dynamics play a key role. We investigated the thermodynamic and magnetic properties of the solar atmosphere during the rise, peak, and decay phases of a C5.1-class flare and filament eruption in active region NOAA 12561 on 2016 July 7 to understand the origin and atmospheric response of this event. High spatial and spectral resolution spectropolarimetric observations of the chromospheric Ca II 8542 Å line and nearby photospheric lines were obtained with the TRIPPEL-SP spectropolarimeter at the Swedish 1-m Solar Telescope. Using nonlocal thermodynamic equilibrium (NLTE) inversions and non-force-free field (NFFF) magnetic extrapolations, we followed the event’s evolution from its precursor to its decay. Before the flare, our analysis reveals a complex, sheared magnetic topology with a high free energy content (∼2 × 10 30 erg). In this precursor phase, we detected persistent localized heating (temperature increase of ∼2000 K) with strong downflows (∼10–20 km s −1 ) deep in the atmosphere. This heating was co-spatial with a bald-patch region, suggesting that low-altitude magnetic reconnection could destabilize the filament of the region. The flare’s rise phase was marked by the filament’s eruption, with a total speed greater than ∼70 km s −1 , when combining inversions and plane-of-sky motions. Following the eruption, the free energy decreased by ∼30% as post-flare loops formed, connecting the flare ribbons and channeling the released energy into the lower atmosphere. The flare ribbons exhibited significant heating to ∼8500 K and downflows up to ∼10 km s −1 , consistent with energy deposition along reconnected loops.

Abstract The detection of circularly polarized, low-frequency radio emission offers the tantalizing possibility of observing interactions between stars and their possible substellar companions, as well as direct emission from exoplanets. Additional follow-up of systems with radio emission is key to understanding the true origin of the emission, since multiple astrophysical mechanisms can plausibly lead to such signals. While 19 M dwarfs were detected by the LOw-Frequency ARray in circular polarization as part of the V-LoTSS survey, HD 220242 is the only F star to have a circularly polarized, low-frequency radio detection in the same survey. We conducted radial velocity (RV) follow-up with the Habitable-zone Planet Finder and combined these observations with additional archival RVs and Hipparcos-Gaia proper motion accelerations to determine that HD 220242 has a stellar companion with P = 16.79 ± 0.04 yr and a mass of 0.619 ± 0.014 M ⊙ . We use spectral energy distribution fitting and lack of any UV excess to rule out a coevolved white dwarf companion, and confirm that the companion is an M dwarf star. Given that F stars lack the coronal properties to produce such coherent emission, and the companion mass and lack of UV excess are consistent with an M dwarf, the radio emission is most plausibly associated with the companion.

Abstract Owing to hot and inflated envelopes that facilitate atmospheric studies, ultrahot Jupiters (UHJs) have attracted much attention. Significant progress has been achieved, from enlarging the sample size to broadening the studies to encompass diverse stellar types and ages. Here, we present a transmission spectroscopy study of HAT-P-70b, a UHJ orbiting a young A-type star, through high-resolution observations with CARMENES at the 3.5 m Calar Alto telescope. By using the line-by-line technique, we confirm the previous detections of H α , Na i , and Ca ii , report a new tentative detection of K i , and impose an upper limit on the He triplet absorption. Through cross-correlation analysis, we identify the Ca ii and Fe i absorptions, both blueshifted by approximately 5 km s −1 , indicating a day-to-night side atmospheric wind. Additionally, we find a new tentative detection of K i . We do not see any significant atmospheric molecular signal in the near-infrared data. Putting HAT-P-70b in the context of UHJs from the literature, it turns out that (1) H α absorption is more common on gas giants orbiting stars younger than 1 Gyr, with a relative detection probability of P Age<1 Gyr (H α )/ P Age≥1 Gyr (H α ) ∼ 3; (2) any UHJ is likely to exhibit Fe i absorption if it has Ca ii .

Aims. Even though magnetic fields play an important role in galaxy evolution, the redshift evolution of galactic-scale magnetic fields is not well constrained observationally. In this paper we provide an observational constraint on the timescale of the mean-field dynamo, and derive the magnetic field in a distant galaxy at z = 0.414. Methods. We obtained broadband spectro-polarimetric 1−8 GHz Very Large Array observations of the lensing system B1600+434, which is a background quasar gravitationally lensed by a foreground spiral galaxy into two images. We applied rotation measure (RM) synthesis and Stokes QU fitting to derive the RM of the two lensed images, which we used to estimate the lensing galaxy’s magnetic field. Results. We measured the RM difference between the lensed images and detected Faraday dispersion caused by the magneto-ionic medium of the lensing galaxy at z = 0.414. Assuming that the RM difference is due to the large-scale regular field of the galaxy’s halo, we measured a coherent magnetic field with a strength of 0.2−3.0 μG at 0.7 kpc and 0.01−2.8 μG at 6.2 kpc vertical distance from the disk of the galaxy. We derive an upper limit on the dynamo e-folding time: τ dynamo < 2.9 × 10 8 yr. We find turbulence on scales below 50 pc and a turbulent field strength of 0.2−12.1 μG. Conclusions. We measured the magnetic field in the halo of a spiral galaxy and find turbulence on scales of < 50 pc. If the RM difference is due to large-scale fields, our result follows the expectation from mean-field dynamo theory and shows that galaxies at z ≃ 0.4 already have magnetic field strengths similar to present-day galaxies. There is one caveat, however: we note the possibility of the turbulent field of the lensing galaxy contributing to the observed RM difference.

Context . Transmission spectra of Neptune-sized exoplanets are frequently observed to be featureless at low-to-mid resolutions from space; whereas high-altitude clouds can mute spectral features, high atmospheric metallicities can also result in compressed envelopes, where low scale heights may also yield undetectable signatures. Aims . We aim to study the atmospheric properties of the warm Neptune GJ 436 b by combining a set of five transit events observed with the CARMENES spectrograph with one transit from CRIRES + so as to provide the most constrained results possible at high resolution. Methods . We removed telluric and stellar signals from the data using SysRem and potential planetary signals were investigated using the cross-correlation technique. Following standard procedures for undetected species, we performed injection recovery tests and Bayesian retrievals to place constraints on the detectability of the main near-infrared absorbers. In addition, we simulated ELT/ANDES observations by computing end-to-end in silico datasets with EXoPLORE . Results . No molecular signals were detected in the atmosphere of GJ 436 b, which is consistent with previous studies. Combined CARMENES-CRIRES + injection-recovery and Bayesian retrieval analyses show that the atmosphere is likely covered by high-altitude clouds (~1 mbar) at low and intermediate metallicities or, alternatively, is very metal-rich (≳ 900× solar), which would suppress spectral features without invoking clouds. Simulations of ELT/ANDES observations suggest a boost by nearly an order of magnitude to the upper limit in the photon-limited regime, reaching 0.1 mbar at 10-300× solar metallicities. Conclusions . The joint analysis of all useful transit observations from CARMENES and CRIRES + provides the most stringent constraints to date on the atmospheric properties of GJ 436 b. Complementary CCF-based and retrieval approaches consistently indicate that the atmosphere is either cloudy or highly metal enriched. Any weak near-infrared absorption lines, if present, are likely to be below current detection limits. However, according to our simulations, these features may be revealed with ELT/ANDES even in single-transit observations.

ABSTRACT Flares and coronal mass ejections are known to be the dominating high-energy phenomena on cool stars. Superflares were thoroughly investigated using broad-band photometry predominantly from Kepler, K2, and TESS. Here, we present a spectroscopic investigation of superflares on the very active spectroscopic binary CC Eri. We focus on spectroscopic signatures of (super)-flares and line asymmetries with the goal to characterize superflares spectroscopically. In 70 nights of spectroscopic observations obtained at the ESO 1.52-m telescope with the Echelle spectrograph PUCHEROS+ hosted by the PLATOSpec consortium, we identified 31 flares from which two are superflares already from the deduced g$^{\prime }$-band energies. We also find a broad blue-wing asymmetry occurring in the impulsive phase of another superflare which shows great potential to be a prominence eruption. For the second most luminous flare, we find the largest number of excess emissions during the impulsive and gradual flare. We identify the flare to be occurring close to the stellar limb which indicates that the flare was even more energetic than derived from its g$^{\prime }$-band and spectral line energies. We identify more than 60 spectral lines in the spectral range of 4100 and 7200 Å showing excess emission during this flare. We detect continuum enhancements as well as photospheric line fillings during the flare. Generally, we find that depending on the flare energy the number of spectral lines revealing excess emission increases, especially for the more energetic superflares. We therefore conclude that superflares are likely scaled-up versions of less energetic normal flares.

WASP-52 b is an inflated hot Jupiter with a large Roche lobe filling fraction, positioned in the hot Neptune desert. Previous in-transit observations of the helium triplet at 10 833 Å have reported a range of excess absorption values (1.5–5.5%) and a lack of net blueshift relative to the planet’s rest frame, distinguishing it from other escaping atmospheres. This study investigates the extent and morphology of material escaping from WASP-52 b, and we assessed whether its outflow resembles a stream-like structure, as suggested for HAT-P-67 b and HAT-P-32 b. We obtained high-resolution spectra with CRIRES + and CARMENES, covering a broader orbital phase range ( φ ≈ ±0.1, ±0.2, 0.5) than previous studies. By analyzing the He I 10 833 Å line as a tracer of escape, we searched for extended absorption beyond transit. Additionally, we explored possible outflow morphologies with three-dimensional (3D) hydrodynamic simulations, coupled with an improved radiative transfer approach, assessing the He I 10 833 Å triplet. The helium line shows no significant evidence of planetary material at the orbital phases observed in this work, though 3D modeling suggests such a structure could exist below observational detection limits. We conclude that the atmospheric outflow of WASP-52 b can be characterized by an intermediate hydrodynamic escape parameter, placing it in a transitional regime between cold outflows forming a stream-like morphology and hot outflows forming a tail. Additionally, the absence of a detectable in-transit blueshift in the helium line rules out a strong day-to-nightside anisotropy scenario.

The spin-orbit angle between a stellar spin axis and its planetary orbital axis is a key diagnostic of planetary migration pathways, yet the mechanisms shaping the observed spin-orbit distribution remain incompletely understood. Combining the spin–orbit angle with atmospheric measurements has emerged as a powerful method of studying exoplanets that showcases the synergy between ground-and space-based observations. We present the Rossiter-McLaughlin effect measurements of the projected spin-orbit angle ( λ ) for three gaseous exoplanets using the newly commissioned PLATOSpec instrument on the E152 Telescope at La Silla Observatory. For WASP-35b, we determine λ = 1 −18 +19 deg, demonstrating PLATOSpec’s capabilities through excellent agreement with HARPS-N literature data. We provide the first spin-orbit measurements for TOI-622b ( λ = −4 ± 12 deg, true spin-orbit angle ψ = 16.1 −9.7 +8.0 deg), revealing an aligned orbit consistent with quiescent disk migration. For K2-237b, we find λ = 91 ± 7 deg and ψ = 90.5 −6.2 +6.8 deg, indicating a nearly perfect polar orbit, which suggests a history consistent with disk-free migration, contrasting with previous studies inferring disk migration. TOI-622b populates a sparsely populated region of sub-Jovian planets with measured spin-orbit angles orbiting stars above the Kraft break, while K2-237b’s polar configuration strengthens tentative evidence of preferential orbital orientations. All three systems are compelling targets for future atmospheric characterization, and these dynamical constraints will be vital for a comprehensive understanding of their formation and evolution.