AOP Open Repository: Recent submissions
Now showing items 1-20 of 986
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NGTS-31b and NGTS-32b: two inflated hot Jupiters orbiting subgiant starsWe present the discoveries of NGTS-31b(= TOI-2721), and NGTS-32b, two hot Jupiters from the Next Generation Transit Survey (NGTS) transiting slightly evolved stars. The orbital periods, radii, and masses are 4.16 and 3.31 d, 1.61 and 1.42 <inline-formula><tex-math id=TM0001 notation=LaTeX>$R_{J}$</tex-math></inline-formula>, and 1.12 and 0.57 <inline-formula><tex-math id=TM0002 notation=LaTeX>$M_{J}$</tex-math></inline-formula>, respectively. Both planets have an incident stellar flux significantly above the threshold where inflation occurs, with both planets showing signs of inflation. These planets have widely different equilibrium temperatures than other hot Jupiters of similar mass and radius, with NGTS-31b having a significantly lower temperature, and NGTS-32b being hotter. This dichotomy raises the question of how prevalent the roles of other inflation mechanisms are in the radius anomaly phenomena and will help further constrain different inflationary models.
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Leveraging Movement Representation from Contrastive Learning for Asteroid DetectionTo support asteroid-related studies, current motion detectors are utilized to select moving object candidates based on their visualizations and movements in sequences of sky exposures. However, the existing detectors encounter the manual parameter settings which require experts to assign proper parameters. Moreover, although the deep learning approach could automate the detection process, these approaches still require synthetic images and hand-engineered features to improve their performance. In this work, we propose an end-to-end deep learning model consisting of two branches. The first branch is trained with contrastive learning to extract a contrastive feature from sequences of sky exposures. This learning method encourages the model to capture a lower-dimensional representation, ensuring that sequences with moving sources (i.e., potential asteroids) are distinct from those without moving sources. The second branch is designed to learn additional features from the sky exposure sequences, which are then concatenated into the movement features before being processed by subsequent layers for the detection of asteroid candidates. We evaluate our model on sufficiently long-duration sequences and perform a comparative study with detection software. Additionally, we demonstrate the use of our model to suggest potential asteroids using photometry filtering. The proposed model outperforms the baseline model for asteroid streak detection by +7.70% of f1-score. Moreover, our study shows promising performance for long-duration sequences and improvement after adding the contrastive feature. Additionally, we demonstrate the uses of our model with the filtering to detect potential asteroids in wide-field detection using the long-duration sequences. Our model could complement the software as it suggests additional asteroids to its detection result.
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Stellar X-Ray Variability and Planetary Evolution in the DS Tucanae SystemWe present an analysis of four Chandra observations of the 45 Myr old DS Tuc binary system. We observed X-ray variability of both stars on timescales from hours to months, including two strong X-ray flares from star A. The implied flaring rates are in agreement with past observations made with XMM-Newton, though these rates remain imprecise due to the relatively short total observation time. We find a clear, monotonic decline in the quiescent level of the star by a factor of 1.8 across 8 months, suggesting stellar variability that might be due to an activity cycle. If proven through future observations, DS Tuc A would be the youngest star for which a coronal activity cycle has been confirmed. The variation in our flux measurements across the four visits is also consistent with the scatter in empirical stellar X-ray relationships with Rossby number. In simulations of the possible evolution of the currently super-Neptune-sized planet DS Tuc A b, we find a range of scenarios for the planet once it reaches a typical field age of 5 Gyr, from Neptune size down to a completely stripped super-Earth. Improved constraints on the planet's mass in the future would significantly narrow these possibilities. We advocate for further Chandra observations to better constrain the variability of this important system.
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A search for close binary systems in the SALT survey of hydrogen-deficient stars using TESSThe TESS periodograms of the SALT survey catalogue of hydrogen-deficient stars were searched for evidence of short-period variability. Periodic light-curve variations were identified in 16 stars out of 153 catalogue objects, of which 10 were false positives. From the remaining 6 identified variables, Ton S 415 is a known close binary system and the sixth close binary containing a hydrogen-deficient hot subdwarf. Radial velocity and SED analyses ruled out the remaining 5 as close binary systems; the causes of their variability remain uncertain. With one or more K-type companions, BPS CS 22956-0094 may be a wide binary or triple. From this SALT + TESS sample, the fraction of close binaries stands at <inline-formula><tex-math id=TM0001 notation=LaTeX>$1/29 \approx 3.5~{{\ \rm per\ cent}}$</tex-math></inline-formula> for intermediate helium hot subdwarfs and <inline-formula><tex-math id=TM0002 notation=LaTeX>$0/124 = 0~{{\ \rm per\ cent}}$</tex-math></inline-formula> for extreme helium subdwarfs.
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Polarimetry of Solar System minor bodies and planets: Polarimetry of Solar System minor bodies and planetsThe study of the polarisation of light is a powerful tool for probing the physical and compositional properties of astrophysical sources, including Solar System objects. In this article, we provide a comprehensive overview of the state-of-the-art in polarimetric studies of various celestial bodies within our Solar System: planets, moons, asteroids, and comets. Additionally, we review relevant laboratory measurements and summarise the fundamental principles of polarimetric observational techniques.
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WISDOM Project - XXII. A 5 per cent precision CO-dynamical supermassive black hole mass measurement in the galaxy NGC 383We present a measurement of the supermassive black hole (SMBH) mass of the nearby lenticular galaxy NGC 383, based on Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the <inline-formula><tex-math id=TM0001 notation=LaTeX>$^{12}$</tex-math></inline-formula>CO(2-1) emission line with an angular resolution of <inline-formula><tex-math id=TM0002 notation=LaTeX>$0.050{\,\rm arcsec}\times 0.024{\,\rm arcsec}$</tex-math></inline-formula> (<inline-formula><tex-math id=TM0003 notation=LaTeX>$\approx 16\times 8$</tex-math></inline-formula> pc<inline-formula><tex-math id=TM0004 notation=LaTeX>$^2$</tex-math></inline-formula>). These observations spatially resolve the nuclear molecular gas disc down to <inline-formula><tex-math id=TM0005 notation=LaTeX>$\approx 41\,300$</tex-math></inline-formula> Schwarzschild radii and the SMBH sphere of influence by a factor of <inline-formula><tex-math id=TM0006 notation=LaTeX>$\approx 24$</tex-math></inline-formula> radially, better than any other SMBH mass measurement using molecular gas to date. The high resolution enables us to probe material with a maximum circular velocity of <inline-formula><tex-math id=TM0007 notation=LaTeX>$\approx 1040$</tex-math></inline-formula> km s<inline-formula><tex-math id=TM0008 notation=LaTeX>$^{-1}$</tex-math></inline-formula>, even higher than those of the highest resolution SMBH mass measurements using megamasers. We detect a clear Keplerian increase (from the outside in) of the line-of-sight rotation velocities, a slight offset between the gas disc kinematic (i.e. the position of the SMBH) and morphological (i.e. the centre of the molecular gas emission) centres, an asymmetry of the innermost rotation velocity peaks and evidence for a mild position angle warp and/or non-circular motions within the central <inline-formula><tex-math id=TM0009 notation=LaTeX>$\approx 0.3\,{\rm arcsec}$</tex-math></inline-formula>. By forward modelling the mass distribution and ALMA data cube, we infer an SMBH mass of <inline-formula><tex-math id=TM0010 notation=LaTeX>$(3.58\pm 0.19)\times 10^9$</tex-math></inline-formula> M<inline-formula><tex-math id=TM0011 notation=LaTeX>$_\odot$</tex-math></inline-formula> (<inline-formula><tex-math id=TM0012 notation=LaTeX>$1\sigma$</tex-math></inline-formula> confidence interval), more precise (5 per cent) but consistent within <inline-formula><tex-math id=TM0013 notation=LaTeX>$\approx 1.4\sigma$</tex-math></inline-formula> with the previous measurement using lower resolution molecular gas data. Our measurement emphasizes the importance of high spatial resolution observations for precise SMBH mass determinations.
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Cross Validation of Albedo Determination for 1627 Ivar from Three Different TechniquesNear-Earth asteroids are of great interest to the scientific community due to their proximity to Earth, making them both potential hazards and possible targets for future missions, as they are relatively easy to reach by spacecraft. A number of techniques and models can be used to constrain their physical parameters and build a comprehensive assessment of these objects. In this work, we compare physical property results obtained from improved H<SUB>V</SUB> absolute magnitude values, thermophysical modeling, and polarimetry data for the well-known Amor-class NEO 1627 Ivar. We show that our fits for albedo are consistent with each other, thus demonstrating the validity of this cross-referencing approach, and propose a value for Ivar's albedo of <inline-formula> </inline-formula>. Future observations will extend this work to a larger sample size, increasing the reliability of polarimetry for rapid asteroid property characterization as a technique independent of previously established methods and requiring significantly fewer observations.
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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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SN 2023tsz: a helium-interaction-driven supernova in a very low-mass galaxySN 2023tsz is a Type Ibn supernova (SN Ibn), an uncommon subtype of stripped-envelope core-collapse supernovae (SNe), discovered in an extremely low-mass host. SNe Ibn are characterized by narrow helium emission lines in their spectra and are believed to originate from the collapse of massive Wolf-Rayet (WR) stars, though their progenitor systems still remain poorly understood. In terms of energetics and spectrophotometric evolution, SN 2023tsz is largely a typical example of the class, although line profile asymmetries in the nebular phase are seen, which may indicate the presence of dust formation or unshocked circumstellar material. Intriguingly, SN 2023tsz is located in an extraordinarily low-mass host galaxy that is in the second percentile for stripped-envelope SN host masses and star formation rates (SFRs). The host has a radius of 1.0 kpc, a g-band absolute magnitude of <inline-formula><tex-math id=TM0002 notation=LaTeX>$-12.72 \pm 0.05$</tex-math></inline-formula>, and an estimated metallicity of <inline-formula><tex-math id=TM0003 notation=LaTeX>$\log (Z_{*}/{\rm Z}_{\odot }) \approx -1.6$</tex-math></inline-formula>. The SFR and metallicity of the host galaxy raise questions about the progenitor of SN 2023tsz. The low SFR suggests that a star with sufficient mass to evolve into a WR would be uncommon in this galaxy. Further, the very low metallicity is a challenge for single stellar evolution to enable H and He stripping of the progenitor and produce an SN Ibn explosion. The host galaxy of SN 2023tsz adds another piece to the ongoing puzzle of SNe Ibn progenitors, and demonstrates that they can occur in hosts too faint to be observed in contemporary sky surveys at a more typical SN Ibn redshift.
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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 First Taste of MEAD (Measuring Extinction and Abundances of Dust). I. Diffuse Milky Way Interstellar Dust Extinction Features in JWST Infrared SpectraWe present the initial results of the Measuring Extinction and Abundances of Dust project, with a focus on the dust extinction features observed in our JWST near- and mid-infrared spectra of nine diffuse Milky Way sightlines (1.2 ≤ A(V) ≤ 2.5). For the first time, we find strong correlations between the 10 μm silicate feature strength and the column densities of Mg, Fe, and O in dust. This is consistent with the well-established theory that Mg- and Fe-rich silicates are responsible for this feature. We obtain an average stoichiometry of the silicate grains in our sample of Mg:Fe:O = 1.1:1:11.2, constraining the grain composition. We find variations in the feature properties, indicating that different sightlines contain different types of silicates. In the average spectrum of our sample, we tentatively detect features around 3.4 and 6.2 μm, which are likely caused by aliphatic and aromatic/olefinic hydrocarbons, respectively. If real, to the best of our knowledge, this is the first detection of hydrocarbons in purely diffuse sightlines with A(V) ≤ 2.5, confirming the presence of these grains in diffuse environments. We detected a 3 μm feature toward HD073882 and tentatively in the sample average, likely caused by water ice (or solid-state water trapped on silicate grains). If confirmed, to the best of our knowledge, this is the first detection of ice in purely diffuse sightlines with A(V) ≤ 2.5, supporting previous findings that these molecules can exist in the diffuse interstellar medium.
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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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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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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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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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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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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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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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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.
