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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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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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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.