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NGTS-33b: a young super-Jupiter hosted by a fast-rotating massive hot starIn the last few decades, planet search surveys have been focusing on solar-type stars, and only recently the high-mass regimes. This is mostly due to challenges arising from the lack of instrumental precision, and more importantly, the inherent active nature of fast-rotating massive stars. Here, we report NGTS-33b (TOI-6442b), a super-Jupiter planet with mass, radius, and orbital period of 3.6 <inline-formula><tex-math id=TM0001 notation=LaTeX>$\pm$</tex-math></inline-formula> 0.3 M<inline-formula><tex-math id=TM0002 notation=LaTeX>$_{\rm J}$</tex-math></inline-formula>, 1.64 <inline-formula><tex-math id=TM0003 notation=LaTeX>$\pm$</tex-math></inline-formula> 0.07 R<inline-formula><tex-math id=TM0004 notation=LaTeX>$_{\rm J}$</tex-math></inline-formula>, and <inline-formula><tex-math id=TM0005 notation=LaTeX>$2.827\,972 \pm 0.000\,001$</tex-math></inline-formula> d, respectively. The host is a fast-rotating (<inline-formula><tex-math id=TM0006 notation=LaTeX>$0.6654 \pm 0.0006$</tex-math></inline-formula> d) and hot (T<inline-formula><tex-math id=TM0007 notation=LaTeX>$_{\rm eff}$</tex-math></inline-formula> = 7437 <inline-formula><tex-math id=TM0008 notation=LaTeX>$\pm$</tex-math></inline-formula> 72 K) A9V type star, with a mass and radius of 1.60 <inline-formula><tex-math id=TM0009 notation=LaTeX>$\pm$</tex-math></inline-formula> 0.11 M<inline-formula><tex-math id=TM0010 notation=LaTeX>$_{\odot }$</tex-math></inline-formula> and 1.47 <inline-formula><tex-math id=TM0011 notation=LaTeX>$\pm$</tex-math></inline-formula> 0.06 R<inline-formula><tex-math id=TM0012 notation=LaTeX>$_{\odot }$</tex-math></inline-formula>, respectively. Planet structure and gyrochronology models show that NGTS-33 is also very young with age limits of 10-50 Myr. In addition, membership analysis points towards the star being part of the Vela OB2 association, which has an age of <inline-formula><tex-math id=TM0013 notation=LaTeX>$\sim$</tex-math></inline-formula> 20-35 Myr, thus providing further evidence about the young nature of NGTS-33. Its low bulk density of 0.19<inline-formula><tex-math id=TM0014 notation=LaTeX>$\pm$</tex-math></inline-formula>0.03 g cm<inline-formula><tex-math id=TM0015 notation=LaTeX>$^{-3}$</tex-math></inline-formula> is 13 per cent smaller than expected when compared to transiting hot Jupiters (HJs) with similar masses. Such cannot be solely explained by its age, where an up to 15 per cent inflated atmosphere is expected from planet structure models. Finally, we found that its emission spectroscopy metric is similar to JWST community targets, making the planet an interesting target for atmospheric follow-up. Therefore, NGTS-33b's discovery will not only add to the scarce population of young, massive and HJs, but will also help place further strong constraints on current formation and evolution models for such planetary systems.
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A Tale of Three: Magnetic Fields along the Orion Integral-shaped Filament as Revealed by the JCMT BISTRO SurveyAs part of the B-fields In Star-forming Region Observations survey, we present James Clerk Maxwell Telescope (JCMT) 850 μm polarimetric observations toward the Orion integral-shaped filament (ISF) that covers three portions known as OMC-1, OMC-2, and OMC-3. The magnetic field threading the ISF seen in the JCMT POL-2 map appears as a tale of three: pinched for OMC-1, twisted for OMC-2, and nearly uniform for OMC-3. A multiscale analysis shows that the magnetic field structure in OMC-3 is very consistent at all the scales, whereas the field structure in OMC-2 shows no correlation across different scales. In OMC-1, the field retains its mean orientation from large to small scales but shows some deviations at small scales. Histograms of relative orientations between the magnetic field and filaments reveal a bimodal distribution for OMC-1, a relatively random distribution for OMC-2, and a distribution with a predominant peak at 90<SUP>∘</SUP> for OMC-3. Furthermore, the magnetic fields in OMC-1 and OMC-3 both appear to be aligned perpendicular to the fibers, which are denser structures within the filament, but the field in OMC-2 is aligned along with the fibers. All these suggest that gravity, turbulence, and magnetic field are each playing a leading role in OMC-1, 2, and 3, respectively. While OMC-2 and 3 have almost the same gas mass, density, and nonthermal velocity dispersion, there are on average younger and fewer young stellar objects in OMC-3, providing evidence that a stronger magnetic field will induce slower and less efficient star formation in molecular clouds.
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ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Nested Morphological and Kinematic Structures of Outflows Revealed in SiO and CO EmissionThe Atacama Large Millimeter/submillimeter Array Survey of Orion Planck Galactic Cold Clumps (ALMASOP) reveals complex nested morphological and kinematic features of molecular outflows through the CO (J = 2‑1) and SiO (J = 5‑4) emission. We characterize the jet and outflow kinematics of the ALMASOP sample in four representative sources (HOPS 10, 315, 358, and G203.21-11.20W2) through channel maps and position–velocity diagrams (PVDs) parallel and transverse to the outflow axes. The combined CO and SiO emission exhibits the coexistence of the conventional extremely high-velocity jets and shell-like low-velocity cavity walls and new features. More complex, nested bubble-like and filamentary structures in the images and channel maps, triangle-shaped regions near the base of the parallel PVDs, and regions composed of rhombus/oval shapes in the transverse PVDs are also evident. Such features find natural explanations within the bubble structure of the unified model of jet, wind, and ambient medium. The reverse shock cavity is revealed on the PVD base regions, and other features naturally arise within the dynamic postshock region of magnetic interaction. The finer nested shells observed within the compressed wind region reveal previously unnoticed shocked emission between the jet and the conventional large cavity walls. These pseudopulse-produced filamentary features connect to the jetlike knotty blobs, creating an impression of episodicity in mass ejection. SiO emission is enhanced downstream of the reverse shock boundary, with jetlike excitation conditions. Combined, these observed features reveal the extended structures induced by the magnetic interplay between a jet-bearing magnetized wide-angle wind and its ambient magnetized surrounding medium.
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Strong magnetic fields of old white dwarfs are symmetric about the stellar rotation axesMany magnetic white dwarfs exhibit a polarised spectrum that periodically varies as the star rotates because the magnetic field is not symmetric about the rotation axis. In this work, we report the discovery that while weakly magnetic white dwarfs of all ages with M ≤ 1 M<SUB>⊙</SUB> show polarimetric variability with a period between hours and several days, the large majority of magnetic white dwarfs in the same mass range with cooling ages older than 2 Gyr and field strengths ≥ 10 MG show little or no polarimetric variability. This could be interpreted as extremely slow rotation, but a lack of known white dwarfs with measured periods longer than two weeks means that we do not see white dwarfs slowing their rotation. We therefore suggest a different interpretation: old strongly magnetic white dwarfs do not vary because their fields are roughly symmetric about the rotation axes. Symmetry may either be a consequence of field evolution or a physical characteristic intrinsic to the way strong fields are generated in older stars. Specifically, a strong magnetic field could distort the shape of a star, forcing the principal axis of maximum inertia away from the spin axis. Eventually, as a result of energy dissipation, the magnetic axis will align with the angular momentum axis. We also find that the higher-mass strongly magnetised white dwarfs, which are likely the products of the merging of two white dwarfs, may appear as either polarimetrically variable or constant. This may be the symptom of two different formation channels or the consequence of the fact that a dynamo operating during a merger may produce diverse magnetic configurations. Alternatively, the massive white dwarfs with constant polarisation may be rotating with periods much shorter than the typical exposure times of the observations.
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X-Shooting ULLYSES: Massive stars at low metallicity: VII. Stellar and wind properties of B supergiants in the Small Magellanic CloudContext. With the aim of understanding massive stars and their feedback in the early epochs of our Universe, the ULLYSES and XShootU collaborations collected the biggest homogeneous dataset of high-quality hot star spectra at low metallicity. Within the rich zoo of massive star stellar types, B supergiants (BSGs) represent an important connection between the main sequence and more extreme evolutionary stages. Additionally, lying toward the cool end of the hot star regime, determining their wind properties is crucial to gauging our expectations on the evolution and feedback of massive stars as, for instance, they are implicated in the bi-stability jump phenomenon. Aims. Here, we undertake a detailed analysis of a representative sample of 18 Small Magellanic Cloud (SMC) BSGs within the ULLYSES dataset. Our UV and optical analysis samples early- and late-type BSGs (from B0 to B8), covering the bi-stability jump region. Our aim is to evaluate their evolutionary status and verify what their wind properties say about the bi-stability jump at a low-metallicity environment. Methods. We used the stellar atmosphere code CMFGEN to model the UV and optical spectra of the sample BSGs as well as photometry in different bands. The optical range encodes photospheric properties, while the wind information resides mostly in the UV. Further, we compare our results with different evolutionary models, with previous determinations in the literature of OB stars, and with diverging mass-loss prescriptions at the bi-stability jump. Additionally, for the first time we provide BSG models in the SMC including X-rays. Results. Our analysis yielded the following main results: (i) From a single-stellar evolution perspective, the evolutionary status of early BSGs appear less clear than late BSGs, which are agree reasonably well with H-shell burning models. (ii) Ultraviolet analysis shows evidence that the BSGs contain X-rays in their atmospheres, for which we provide constraints. In general, higher X-ray luminosity (close to the standard log(L<SUB>X</SUB>/L) ~ ‑7) is favored for early BSGs, despite associated degeneracies. For later-type BSGs, lower values are preferred, log(L<SUB>X</SUB>/L) ~ ‑8.5. (iii) The obtained mass-loss rates suggest neither a jump nor an unperturbed monotonic decrease with temperature. Instead, a rather constant trend appears to happen, which is at odds with the increase found for Galactic BSGs. (iv) The wind velocity behavior with temperature shows a sharp drop at ~19 kK, very similar to the bi-stability jump observed for Galactic stars.
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Stellar expansion or inflation?While stellar expansion after core-hydrogen exhaustion related to thermal imbalance has been documented for decades, the physical phenomenon of stellar inflation that occurs close to the Eddington limit has only come to the fore in recent years. We aim to elucidate the differences between these physical mechanisms for stellar radius enlargement, especially given that additional terms such as 'bloated' and 'puffed-up' stars have been introduced in the recent massive star literature. We employ single and binary star MESA structure and evolution models for constant mass, as well as models allowing the mass to change due to winds or binary interaction. We find cases that were previously attributed to stellar inflation in fact to be due to stellar expansion. We also highlight that while the opposite effect of expansion is contraction, the removal of an inflated zone should not be referred to as contraction but rather deflation, as the star is still in thermal balance.
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Cataclysmic Variables and AM CVn Binaries in SRG/eROSITA + Gaia: Volume Limited Samples, X-Ray Luminosity Functions, and Space DensitiesWe present volume-limited samples of cataclysmic variables (CVs) and AM CVn binaries jointly selected from SRG/eROSITA eRASS1 and Gaia DR3 using an X-ray + optical color–color diagram (the X-ray Main Sequence). This tool identifies all CV subtypes, including magnetic and low-accretion rate systems, in contrast to most previous surveys. We find 23 CVs, 3 of which are AM CVns, out to 150 pc in the Western Galactic Hemisphere. Our 150 pc sample is spectroscopically verified and complete down to L<SUB>X</SUB> = 1.3 × 10<SUP>29</SUP> erg s<SUP>‑1</SUP> in the 0.2–2.3 keV band, and we also present CV candidates out to 300 pc and 1000 pc. We discovered two previously unknown systems in our 150 pc sample: the third nearest AM CVn and a magnetic period bouncer. We find the mean L<SUB>X</SUB> of CVs to be <L<SUB>X</SUB>> ≈ 4.6 × 10<SUP>30</SUP> erg s<SUP>‑1</SUP>, in contrast to previous surveys which yielded <L<SUB>X</SUB>> ∼ 10<SUP>31</SUP>‑10<SUP>32</SUP> erg s<SUP>‑1</SUP>. We construct X-ray luminosity functions that, for the first time, flatten out at L<SUB>X</SUB> ∼ 10<SUP>30</SUP> erg s<SUP>‑1</SUP>. We infer average number, mass, and luminosity densities of ρ<SUB>N,CV</SUB> = (3.7 ± 0.7) × 10<SUP>‑6</SUP>pc<SUP>‑3</SUP>, <inline-formula> <mml:math overflow=scroll><mml:msub><mml:mrow><mml:mi>ρ</mml:mi></mml:mrow><mml:mrow><mml:mi>M</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mo stretchy=false>(</mml:mo><mml:mn>5.0</mml:mn><mml:mo>±</mml:mo><mml:mn>1.0</mml:mn><mml:mo stretchy=false>)</mml:mo><mml:mo>×</mml:mo><mml:mn>1</mml:mn><mml:msup><mml:mrow><mml:mn>0</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>5</mml:mn></mml:mrow></mml:msup><mml:msubsup><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msubsup></mml:math> </inline-formula>, and <inline-formula> <mml:math overflow=scroll><mml:msub><mml:mi>ρ</mml:mi><mml:msub><mml:mi>L</mml:mi><mml:mi mathvariant=normal>X</mml:mi></mml:msub></mml:msub><mml:mo>=</mml:mo><mml:mo stretchy=false>(</mml:mo><mml:mn>2.3</mml:mn><mml:mo>±</mml:mo><mml:mn>0.4</mml:mn><mml:mo stretchy=false>)</mml:mo><mml:mo>×</mml:mo><mml:mn>1</mml:mn><mml:msup><mml:mn>0</mml:mn><mml:mn>26</mml:mn></mml:msup><mml:mspace width=0.25em></mml:mspace><mml:mi>erg</mml:mi><mml:mspace width=0.25em></mml:mspace><mml:msup><mml:mi mathvariant=normal>s</mml:mi><mml:mrow><mml:mo>‑</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup><mml:msubsup><mml:mi>M</mml:mi><mml:mo>⊙</mml:mo><mml:mrow><mml:mo>‑</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msubsup></mml:math> </inline-formula>, respectively, in the solar neighborhood. Our uniform selection method also allows us to place meaningful estimates on the space density of AM CVns, ρ<SUB>N,AM CVn</SUB> = (5.5 ± 3.7) × 10<SUP>‑7</SUP> pc<SUP>‑3</SUP>. Magnetic CVs and period bouncers make up 35% and 25% of our sample, respectively. This work, through a novel discovery technique, shows that the observed number densities of CVs and AM CVns, as well as the fraction of period bouncers, are still in tension with population synthesis estimates.
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NGTS-33b: A Young Super-Jupiter Hosted by a Fast Rotating Massive Hot StarIn the last few decades planet search surveys have been focusing on solar type stars, and only recently the high-mass regimes. This is mostly due to challenges arising from the lack of instrumental precision, and more importantly, the inherent active nature of fast rotating massive stars. Here we report NGTS-33b (TOI-6442b), a super-Jupiter planet with mass, radius and orbital period of 3.6 ± 0.3 M<SUB>j</SUB>, 1.64 ± 0.07 R<SUB>j</SUB> and 2.827972 ± 0.000001 days, respectively. The host is a fast rotating (0.6654 ± 0.0006 day) and hot (T<SUB>eff</SUB> = 7437 ± 72 K) A9V type star, with a mass and radius of 1.60 ± 0.11 M<SUB>⊙</SUB> and 1.47 ± 0.06 R<SUB>⊙</SUB>, respectively. Planet structure and Gyrochronology models shows that NGTS-33 is also very young with age limits of 10-50 Myr. In addition, membership analysis points towards the star being part of the Vela OB2 association, which has an age of ~ 20-35 Myr, thus providing further evidences about the young nature of NGTS-33. Its low bulk density of 0.19±0.03 gcm<SUP>-3</SUP> is 13<inline-formula><tex-math id=TM0001 notation=LaTeX>$\%$</tex-math></inline-formula> smaller than expected when compared to transiting hot Jupiters with similar masses. Such cannot be solely explained by its age, where an up to 15<inline-formula><tex-math id=TM0002 notation=LaTeX>$\%$</tex-math></inline-formula> inflated atmosphere is expected from planet structure models. Finally, we found that its emission spectroscopy metric is similar to JWST community targets, making the planet an interesting target for atmospheric follow-up. Therefore, NGTS-33b's discovery will not only add to the scarce population of young, massive and hot Jupiters, but will also help place further strong constraints on current formation and evolution models for such planetary systems.
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ALMASOP. The Localized and Chemically Rich Features near the Bases of the Protostellar Jet in HOPS 87HOPS 87 is a Class 0 protostellar core known to harbor an extremely young bipolar outflow and a hot corino. We report the discovery of localized, chemically rich regions near the bases of the two-lobe bipolar molecular outflow in HOPS 87 containing molecules such as H<SUB>2</SUB>CO, <SUP>13</SUP>CS, H<SUB>2</SUB>S, OCS, and CH<SUB>3</SUB>OH, the simplest complex organic molecule (COM). The locations and kinematics suggest that these localized features are due to jet-driven shocks rather than being part of the hot-corino region encasing the protostar. The COM compositions of the molecular gas in these jet-localized regions are relatively simpler than those in the hot-corino zone. We speculate that this simplicity is due to either the liberation of ice with a less complex chemical history or the effects of shock chemistry. Our study highlights the dynamic interplay between the protostellar bipolar outflow, disk, inner-core environment, and the surrounding medium, contributing to our understanding of molecular complexity in solar-like young stellar objects.
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X-Shooting ULLYSES: Massive stars at low metallicity: VIII. Stellar and wind parameters of newly revealed stripped stars in Be binariesOn the route toward merging neutron stars and stripped-envelope supernovae, binary population synthesis predicts a large number of post-interaction systems with massive stars that have been stripped of their outer layers. However, observations of such stars in the intermediate-mass regime below the Wolf-Rayet masses are rare. Using X-Shooting ULLYSES (XShootU) data, we have discovered three partially stripped star + Be/Oe binaries in the Magellanic Clouds. We analyzed the UV and optical spectra using the Potsdam Wolf-Rayet (PoWR) model atmosphere code by superimposing model spectra that correspond to each component. The estimated current masses of the partially stripped stars fall within the intermediate-mass range of ≈4 ‑ 8 M<SUB>⊙</SUB>. These objects are found to be over-luminous for their corresponding stellar masses, which aligns with the luminosities during core He-burning. Their accompanying Be/Oe secondaries are found to have much higher masses than their stripped primaries (mass ratio ≳2). The surfaces of all three partially stripped stars exhibit clear indications of significant nitrogen enrichment as well as a depletion of carbon and oxygen. Furthermore, one of our sample stars shows signs of substantial helium enrichment. Our study provides the first comprehensive determination of the wind parameters of partially stripped stars in the intermediate-mass range. The wind mass-loss rates of these stars are estimated to be on the order of 10<SUP>‑7</SUP> M<SUB>⊙</SUB> yr<SUP>‑1</SUP>, which is more than ten times higher than that of OB stars with the same luminosity. The current mass-loss recipes commonly employed in evolutionary models to characterize this phase are based on OB or WR mass-loss rates, and they significantly underestimate or overestimate the observed mass-loss rates of (partially) stripped stars by an order of magnitude. Binary evolution models suggest that the observed primaries had initial masses in the range of 12‑17 M<SUB>⊙</SUB>, and are potential candidates for stripped-envelope supernovae resulting in the formation of a neutron star. If these systems survive the explosion, they will likely evolve to become Be X-ray binaries and later double neutron stars.
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A Broadband X-Ray Investigation of Fast-spinning Intermediate Polar CTCV J2056–3014We report on XMM-Newton, NuSTAR, and NICER X-ray observations of CTCV J2056–3014, a cataclysmic variable (CV) with one of the fastest-spinning white dwarfs (WDs) at P = 29.6 s. While previously classified as an intermediate polar, CJ2056 also exhibits the properties of WZ Sge–type CVs, such as dwarf novae and superoutbursts. With XMM-Newton and NICER, we detected the spin period up to ∼2 keV with 7σ significance. We constrained its derivative to <inline-formula> <mml:math overflow=scroll><mml:mo stretchy=false>|</mml:mo><mml:mrow><mml:mover><mml:mi>P</mml:mi><mml:mo>̇</mml:mo></mml:mover></mml:mrow><mml:mo stretchy=false>|</mml:mo><mml:mo><</mml:mo><mml:mn>1.8</mml:mn><mml:mo>×</mml:mo><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>12</mml:mn></mml:mrow></mml:msup></mml:math> </inline-formula> s s<SUP>‑1</SUP> after correcting for binary orbital motion. The pulse profile is characterized by a single broad peak with ∼25% modulation. NuSTAR detected a fourfold increase in unabsorbed X-ray flux coincident with an optical flare, in 2022 November. The XMM-Newton and NICER X-ray spectra at 0.310 keV are best characterized by an absorbed, optically thin three-temperature thermal plasma model (kT = 0.3, 1.0, and 4.9 keV), while the NuSTAR spectra at 3–30 keV are best fit by a single-temperature thermal plasma model (kT = 8.4 keV), both with Fe abundance Z <SUB>Fe</SUB>/Z <SUB>⊙</SUB> = 0.3. CJ2056 exhibits similarities to other fast-spinning CVs, such as low plasma temperatures and no significant X-ray absorption at low energies. As the WD's magnetic field strength is unknown, we applied both nonmagnetic and magnetic CV spectral models (MKCFLOW and MCVSPEC) to determine the WD mass. The derived WD mass range (M = 0.7–1.0 M <SUB>⊙</SUB>) is above the centrifugal breakup mass limit of 0.56 M <SUB>⊙</SUB> and consistent with the mean WD mass of local CVs (M ≈ 0.8–0.9 M <SUB>⊙</SUB>).
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X-Shooting ULLYSES: Massive Stars at low metallicity: IX. Empirical constraints on mass-loss rates and clumping parameters for OB supergiants in the Large Magellanic CloudContext. Current implementations of mass loss for hot, massive stars in stellar evolution models usually include a sharp increase in mass loss when blue supergiants become cooler than T<SUB>eff</SUB> ∼ 20 ‑ 22 kK. Such a drastic mass-loss jump has traditionally been motivated by the potential presence of a so-called bistability ionisation effect, which may occur for line-driven winds in this temperature region due to recombination of important line-driving ions. Aims. We perform quantitative spectroscopy using UV (ULLYSES program) and optical (XShootU collaboration) data for 17 OB-supergiant stars in the LMC (covering the range T<SUB>eff</SUB> ∼ 14 ‑ 32 kK), deriving absolute constraints on global stellar, wind, and clumping parameters. We examine whether there are any empirical signs of a mass-loss jump in the investigated region, and we study the clumped nature of the wind. Methods. We used a combination of the model atmosphere code FASTWIND and the genetic algorithm (GA) code Kiwi-GA to fit synthetic spectra of a multitude of diagnostic spectral lines in the optical and UV. Results. We find an almost monotonic decrease of mass-loss rate with effective temperature, with no signs of any upward mass loss jump anywhere in the examined region. Standard theoretical comparison models, which include a strong bistability jump thus severely overpredict the empirical mass-loss rates on the cool side of the predicted jump. Another key result is that across our sample we find that on average about 40% of the total wind mass seems to reside in the more diluted medium in between dense clumps. Conclusions. Our derived mass-loss rates suggest that for applications such as stellar evolution one should not include a drastic bistability jump in mass loss for stars in the temperature and luminosity region investigated here. The derived high values of interclump density further suggest that the common assumption of an effectively void interclump medium (applied in the vast majority of spectroscopic studies of hot star winds) is not generally valid in this parameter regime.
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Characterizing high and low accretion states in VY Scl CVs using ZTF and TESS dataVY Scl binaries are a sub-class of cataclysmic variable (CV) which show extended low states, but do not show outbursts which are seen in other classes of CV. To better determine how often these systems spend in low states and to resolve the state transitions we have analysed Zwicky Transient Facility (ZTF) data on eight systems and Transiting Exoplanet Survey Satellite (TESS) data on six systems. Half of the sample spent most of the time in a high state; three show a broad range and one spends roughly half the time transitioning between high and low states. Using the ZTF data, we explore the colour variation as a function of brightness. In KR Aur, we identify a series of repeating outburst events whose brightness appears to increase over time. Using TESS data, we searched for periods other than the orbital. In LN UMa, we find evidence for a peak whose period varies between 3 and 6 d. We outline the current models which aim to explain the observed properties of VY Scl systems which includes disc irradiation and a white dwarf having a significant magnetic field.
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X-Shooting ULLYSES: Massive stars at low metallicity: VI. Atmosphere and mass-loss properties of O-type giants in the Small Magellanic CloudContext. Mass loss through a stellar wind is an important physical process that steers the evolution of massive stars and controls the properties of their end-of-life products, such as the supernova type and the mass of compact remnants. To probe its role in stellar evolution over cosmic time, mass loss needs to be studied as function of metallicity. For mass loss to be accurately quantified, the wind structure needs to be established jointly with the characteristics of small-scale inhomogeneities in the outflow, which are known as wind clumping. Aims. We aim to improve empirical estimates of mass loss and wind clumping for hot main-sequence massive stars, study the dependence of both properties on the metal content, and compare the theoretical predictions of mass loss as a function of metallicity to our findings. Methods. Using the model atmosphere code FASTWIND and the genetic algorithm fitting method KIWI-GA, we analyzed the optical and ultraviolet spectra of 13 O-type giant to supergiant stars in the Small Magellanic Cloud galaxy, which has a metallicity of approximately one-fifth of that of the Sun. We quantified the stellar global outflow properties, such as the mass-loss rate and terminal wind velocity, and the wind clumping properties. To probe the role of metallicity, our findings were compared to studies of Galactic and Large Magellanic Cloud samples that were analyzed with similar methods, including the description of clumping. Results. We find significant variations in the wind clumping properties of the target stars, with clumping starting at flow velocities 0.01–0.23 of the terminal wind velocity and reaching clumping factors f<SUB>cl</SUB> = 2–30. In the luminosity (log L/L<SUB>⊙</SUB> = 5.0–6.0) and metallicity (Z/Z<SUB>⊙</SUB> = 0.2–1) range we considered, we find that the scaling of the mass loss M<SUP>˙</SUP> with metallicity Z varies with luminosity. At log L/L<SUB>⊙</SUB> = 5.75, we find M<SUP>˙</SUP> ∝ Z<SUP>m</SUP> with m = 1.02 ± 0.30, in agreement with pioneering work in the field within the uncertainties. For lower luminosities, however, we obtain a significantly steeper scaling of m > 2. Conclusions. The monotonically decreasing m(L) behavior adds a complexity to the functional description of the mass-loss rate of hot massive stars. Although the trend is present in the predictions, it is much weaker than we found here. However, the luminosity range for which m is significantly larger than previously assumed (at log L/L<SUB>⊙</SUB> ≲ 5.4) is still poorly explored, and more studies are needed to thoroughly map the empirical behavior, in particular, at Galactic metallicity.
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Radio signatures of star-planet interactions, exoplanets and space weatherRadio detections of stellar systems provide a window onto stellar magnetic activity and the space weather conditions of extrasolar planets — information that is difficult to obtain at other wavelengths. The maturation of low-frequency radio instruments and the plethora of wide-field radio surveys have driven recent advances in observing auroral emissions from radio-bright low-mass stars and exoplanets. To guide us in putting these recent results in context, we introduce the foremost local analogues for the field: solar bursts and the aurorae found on Jupiter. We detail how radio bursts associated with stellar flares are foundational to the study of stellar coronae, and time-resolved radio dynamic spectra offer one of the best prospects for detecting and characterizing coronal mass ejections from other stars. We highlight the possibility of directly detecting coherent radio emission from exoplanetary magnetospheres, as well as early tentative results. We bridge this discussion with the field of brown dwarf radio emission — the larger and stronger magnetospheres of these stars are amenable to detailed study with current instruments. Bright, coherent radio emission is also predicted from magnetic interactions between stars and close-in planets. We discuss the underlying physics of these interactions and the implications of recent provisional detections for exoplanet characterization. We conclude with an overview of outstanding questions in the theory of stellar, star-planet interaction and exoplanet radio emission and the potential of future facilities to answer them.
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Discovery of three magnetic helium-rich hot subdwarfs with SALTMagnetic fields with strengths ranging from 300 to 500 kG have recently been discovered in a group of four extremely similar helium-rich hot subdwarf (He-sdO) stars. In addition to their strong magnetic fields, these He-sdO stars are characterised by common atmospheric parameters, clustering around T<SUB>eff</SUB> = 46 500 K, a log ɡ/cm s<SUP>‑1</SUP> close to 6, and intermediate helium abundances. Here we present the discovery of three additional magnetic hot subdwarfs, J123359.44–674929.11, J125611.42-575333.45, and J144405.79–674400.93. These stars are again almost identical in terms of atmospheric parameters, but, at B ≈ 200 kG, their magnetic fields are somewhat weaker than those previously known. The close similarity of all known He-sdOs implies a finely tuned formation channel. We propose the merging of a He white dwarf with a H+He white dwarf. A differential rotation at the merger interface may initiate a toroidal magnetic field that evolves via a magnetic dynamo to produce a poloidal field. This field is either directly visible at the surface or might diffuse towards the surface if initially buried. We further discuss a broad absorption line centred at about 4630 Å that is common to all magnetic He-sdOs. This feature may not be related to the magnetic field but instead to the intermediate helium abundances in these He-sdO stars, allowing the strong He II 4686 Å line to be perturbed by collisions with hydrogen atoms.
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Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Our GalaxyAs we learn more about the multi-scale interstellar medium (ISM) of our Galaxy, we develop a greater understanding for the complex relationships between the large-scale diffuse gas and dust in Giant Molecular Clouds (GMCs), how it moves, how it is affected by the nearby massive stars, and which portions of those GMCs eventually collapse into star forming regions. The complex interactions of those gas, dust and stellar populations form what has come to be known as the ecology of our Galaxy. Because we are deeply embedded in the plane of our Galaxy, it takes up a significant fraction of the sky, with complex dust lanes scattered throughout the optically recognizable bands of the Milky Way. These bands become bright at (sub-)millimetre wavelengths, where we can study dust thermal emission and the chemical and kinematic signatures of the gas. To properly study such large-scale environments, requires deep, large area surveys that are not possible with current facilities. Moreover, where stars form, so too do planetary systems, growing from the dust and gas in circumstellar discs, to planets and planetesimal belts. Understanding the evolution of these belts requires deep imaging capable of studying belts around young stellar objects to Kuiper belt analogues around the nearest stars. Here we present a plan for observing the Galactic Plane and circumstellar environments to quantify the physical structure, the magnetic fields, the dynamics, chemistry, star formation, and planetary system evolution of the galaxy in which we live with AtLAST; a concept for a new, 50m single-dish sub-mm telescope with a large field of view which is the only type of facility that will allow us to observe our Galaxy deeply and widely enough to make a leap forward in our understanding of our local ecology.
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Binarity at LOw Metallicity (BLOeM): A spectroscopic VLT monitoring survey of massive stars in the SMCSurveys in the Milky Way and Large Magellanic Cloud have revealed that the majority of massive stars will interact with companions during their lives. However, knowledge of the binary properties of massive stars at low metallicity, and therefore in conditions approaching those of the Early Universe, remain sparse. We present the Binarity at LOw Metallicity (BLOeM) campaign, an ESO large programme designed to obtain 25 epochs of spectroscopy for 929 massive stars in the Small Magellanic Cloud, allowing us to probe multiplicity in the lowest-metallicity conditions to date (Z = 0.2 Z<SUB>⊙</SUB>). BLOeM will provide (i) the binary fraction, (ii) the orbital configurations of systems with periods of P ≲ 3 yr, (iii) dormant black-hole binary candidates (OB+BH), and (iv) a legacy database of physical parameters of massive stars at low metallicity. Main sequence (OB-type) and evolved (OBAF-type) massive stars are observed with the LR02 setup of the GIRAFFE instrument of the Very Large Telescope (3960–4570 Å resolving power R = 6200; typical signal-to-noise ratio(S/N) ≈70–100). This paper utilises the first nine epochs obtained over a three-month time period. We describe the survey and data reduction, perform a spectral classification of the stacked spectra, and construct a Hertzsprung-Russell diagram of the sample via spectral-type and photometric calibrations. Our detailed classification reveals that the sample covers spectral types from O4 to F5, spanning the effective temperature and luminosity ranges 6.5 ≲ T<SUB>eff</SUB>/kK ≲ 45 and 3.7 < log L/L<SUB>⊙</SUB> < 6.1 and initial masses of 8 ≲ M<SUB>ini</SUB> ≲ 80 M<SUB>⊙</SUB>. The sample comprises 159 O-type stars, 331 early B-type (B0–3) dwarfs and giants (luminosity classes V–III), 303 early B-type supergiants (II–I), and 136 late-type BAF supergiants. At least 82 stars are OBe stars: 20 O-type and 62 B-type (13% and 11% of the respective samples). In addition, the sample includes 4 high-mass X-ray binaries, 3 stars resembling luminous blue variables, 2 bloated stripped-star candidates, 2 candidate magnetic stars, and 74 eclipsing binaries.
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Photospheric Observations of Surface and Body Modes in Solar Magnetic PoresOver the past number of years, great strides have been made in identifying the various low-order magnetohydrodynamic wave modes observable in a number of magnetic structures found within the solar atmosphere. However, one aspect of these modes that has remained elusive, until now, is their designation as either surface or body modes. This property has significant implications for how these modes transfer energy from the waveguide to the surrounding plasma. Here, for the first time to our knowledge, we present conclusive, direct evidence of these wave characteristics in numerous pores that were observed to support sausage modes. As well as outlining methods to detect these modes in observations, we make estimates of the energies associated with each mode. We find surface modes more frequently in the data, as well as that surface modes appear to carry more energy than those displaying signatures of body modes. We find frequencies in the range of ∼2-12 mHz, with body modes as high as 11 mHz, but we do not find surface modes above 10 mHz. It is expected that the techniques we have applied will help researchers search for surface and body signatures in other modes and in differing structures from those presented here.
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X-Shooting ULLYSES: Massive stars at low metallicity: V. Effect of metallicity on surface abundances of O starsContext. Massive stars rotate faster, on average, than lower mass stars. Stellar rotation triggers hydrodynamical instabilities which transport angular momentum and chemical species from the core to the surface. Models of high-mass stars that include these processes predict that chemical mixing is stronger at lower metallicity. Aims. We aim to test this prediction by comparing the surface abundances of massive stars at different metallicities. Methods. We performed a spectroscopic analysis of single O stars in the Magellanic Clouds (MCs) based on the ULLYSES and XShootU surveys. We determined the fundamental parameters and helium, carbon, nitrogen, and oxygen surface abundances of 17 LMC and 17 SMC non-supergiant O6–9.5 stars. We complemented these determinations by literature results for additional MCs and also Galactic stars to increase the sample size and metallicity coverage. We investigated the differences in the surface chemical enrichment at different metallicities and compared them with predictions of three sets of evolutionary models. Results. Surface abundances are consistent with CNO-cycle nucleosynthesis. The maximum surface nitrogen enrichment is stronger in MC stars than in Galactic stars. Nitrogen enrichment is also observed in stars with higher surface gravities in the SMC than in the Galaxy. This trend is predicted by models that incorporate chemical transport caused by stellar rotation. The distributions of projected rotational velocities in our samples are likely biased towards slow rotators. Conclusions. A metallicity dependence of surface abundances is demonstrated. The analysis of larger samples with an unbiased distribution of projected rotational velocities is required to better constrain the treatment of chemical mixing and angular momentum transport in massive single and binary stars.
