AOP Open Repository: Recent submissions
Now showing items 1-20 of 922
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The clumped winds of the most massive starsThe core of the cluster R136 in the Large Magellanic Cloud hosts the most massive stars known. The high mass-loss rates of these stars strongly impact their surroundings, as well as the evolution of the stars themselves. To quantify this impact accurate mass-loss rates are needed, however, uncertainty about the degree of inhomogeneity of the winds (`wind clumping'), makes mass-loss measurements uncertain. We combine optical and ultraviolet HST/STIS spectroscopy of 56 stars in the core of R136 in order to put constraints on the wind structure, improving the accuracy of the mass-loss rate measurements. We find that the winds are highly clumped, and use our measured mass-loss rates to test theoretical predictions. Furthermore we find, for the first time, tentative trends in the wind-structure parameters as a function of mass-loss rate, suggesting that the winds of stars with higher mass-loss rates are less clumped than those with lower mass-loss rates.
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Constraining physical processes in pre-supernovae massive star evolutionWhile we have growing numbers of massive star observations, it remains unclear how efficient the key physical processes such as mass loss, convection and rotation are, or indeed how they impact each other. We reconcile this with detailed stellar evolution models, yet these models have their own drawbacks with necessary assumptions for 3-dimensional processes like rotation which need to be adapted into 1-dimensional models. The implementation of empirical mass-loss prescriptions in stellar evolution codes can lead to the extrapolation of base rates to unconstrained evolutionary stages leading to a range of uncertain fates. In short, there remain many free parameters and physical processes which need to be calibrated in order to align our theory better with upcoming observations. We have tested various processes such as mass loss and internal mixing, including rotational mixing and convective overshooting, against multiple observational constraints such as using eclipsing binaries, the Humphreys-Davidson limit, and the final masses of Wolf-Rayet stars, across a range of metallicities. In fact, we developed a method of disentangling the effects of mixing and mass loss in the `Mass-Luminosity Plane' allowing direct calibration of these processes. In all cases, it is important to note that a combined appreciation for both stellar winds and internal mixing are important to reproduce observations.
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Predictions for the Maximum Masses of Black Holes below the PI BoundaryWhile the initial discovery of GW150914 resulted in the detection of black holes larger than initially expected, it was the GW190521 event which truly challenged astrophysical assumptions about stellar evolution and black hole progenitors, as the components of GW190521 were firmly within the traditional Pair-Instability (PI) mass-gap – a range of masses where no black holes were expected to be created due to PI supernovae (PISN). We investigate the possibility that this merger involved first generation black holes, and that the unexpectedly heavy 85 solar mass BH could be produced from fundamental stellar physics. We present the results of studies involving the stellar evolution code MESA, as we systematically vary several parameters of stellar physics (in particular mixing and mass loss) to test assumptions and build a population of potential black hole progenitors within the traditional PI gap.
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A resolved view of the impact of massive star formation in the atomic, molecular and ionized gas in the Carina NebulaThe Carina Nebula Complex (CNC) is a spectacular star-forming region located at 2.3 kpc, which is close enough to observe different size scales in detail. With more than 65 O-stars and more than 900 young stellar objects identified it is also the nearest analogue of more extreme star forming regions, such as 30 Doradus. In this talk I will present the results of a major effort to study the relationship between the different gas phases in the Carina region from 100 pc to 0.01 pc using the Australia Telescope Compact Array (ATCA), the Mopra telescope and ALMA. At large scales, CO image combined with far-infrared data from Herschel revealed the overall molecular mass and its distribution across the CNC (Rebolledo et al. 2016). An extremely detailed map of the HI 21-cm line across the whole nebula revealed a complex filamentary structure in the atomic gas, which allowed the identification of regions where phase transition between atomic and molecular gas is happening (Rebolledo et al. 2017). An ATCA 1-3 GHz radio continuum image across the whole Carina region revealed a complete and spectacular view of the ionized gas in the region (Rebolledo et al. 2021). At small scales, ALMA high spatial resolution observations of molecular line tracers and dust showed that the level of stellar feedback effectively influences the fragmentation process in clumps, and provides further evidence for a higher level of turbulence in the material with a higher level of massive stellar feedback (Rebolledo et al. 2020).
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Pre- and protostellar cores in the 200 brightest Planck compact sourcesThe Planck compact source catalogue provides excellent samples for studying the earliest phases of star formation. Covering all galactic longitudes and latitudes they can give an overview of how star formation varies throughout the Milky Way, enabling a better insight into star formation out of the Galactic plane, where our current understanding is restricted mostly to nearby clouds. We examined the 200 brightest Planck compact sources visible from the northern hemisphere using observations from the James Clerk Maxwell Telescope's SCUBA2 bolometer array. Its high resolution revealed diverse, mostly filamentary structures, and allowed the extraction of point sources from the maps. We classified more than 1500 of these point sources and compiled a catalogue with their positions, sizes, and physical parameters. In our statistical analysis, we investigate properties of star-forming regions at different latitudes, aiming to better understand the flow of interstellar matter in the Galaxy and thus refine our latest view of the Milky Way.
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How to make an 85 Solar Mass Black HoleWe present in-progress resolution test and parameter space studies for very massive stars using MESA, showcasing current MESA version convergence studies.
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CHIMPS2: <SUP>13</SUP>CO J = 3→2 emission in the central molecular zoneWe present the initial data for the $(J = 3 \rightarrow 2)$ transition of $^{13}\text{CO}$ obtained from the central molecular zone (CMZ) of the Milky Way as part of the CO Heterodyne Inner Milky Way Plane Survey 2 (CHIMPS2). Covering $359^{\circ } \le l \le 1^{\circ }$ and $|b| \le 0.5^{\circ }$ with an angular resolution of 19 arcsec, velocity resolution of 1 km s$^{-1}$, and rms $\Delta {T_{\rm A}^{*}} = 0.59\, \mathrm{K}$ at these resolutions, our observations unveil the complex structure of the CMZ molecular gas in improved detail. Complemented by the $\rm {^{12}CO}$ CHIMPS2 data, we estimate a median optical depth of $\tau _{13} = 0.087$. The preliminary analysis yields a median $^{13}\text{CO}$ column-density range equal to $N(^{13}{\rm CO}) = 2{\!-\!}5 \times 10^{18}\, \mathrm{cm}^{-2}$, median H$_{2}$ column density equal to $N(\mathrm{H_{2}}) = 4 \times 10^{22}\, \mathrm{cm}^{-2}$ to $1 \times 10^{23}\, \mathrm{cm}^{-2}$. We derive $N({\rm H_{2}})$-based total mass estimates of $M({\rm H}_{2}) = 2{\!-\!}6 \times 10^{7}\, \mathrm{M}_{\odot }$, in agreement with previous studies. We analyse the relationship between the integrated intensity of $^{13}\text{CO}$ and the surface density of compact sources identified by Herschel Hi-GAL, and find that younger Hi-GAL sources detected at 500 $\rm{\mu m}$ but not at 70 $\rm{\mu m}$ follow the dense gas of the CMZ more closely than those that are bright at 70 $\rm{\mu m}$. The latter, actively star-forming sources appear to be more associated with material in the foreground spiral arms.
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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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On the Z-(in)dependence of the Humphreys-Davidson LimitThe temperature independent part of the Humphreys-Davidson (HD) limit sets the boundary for evolutionary channels of massive stars that either end their lives as red supergiants (RSGs) or as the hotter blue supergiants (BSGs) and Wolf-Rayet stars. Recent downward revision of most luminous RSGs the Galaxy below log(L / L<SUB>⊙</SUB>) ≈ 5.5, more in line with the Magellanic Clouds, might hint towards a metallicity (Z)-independent HD limit. We present MESA single star models in the 15-40 M<SUB>⊙</SUB> range and study the different Z-dependent processes that could potentially affect the location of the upper luminosity limit of RSGs.
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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.
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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.
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X-Shooting ULLYSES: Massive stars at low metallicity. II. DR1: Advanced optical data products for the Magellanic CloudsContext. The XShootU project aims to obtain ground-based optical to near-infrared spectroscopy of all targets observed by the Hubble Space Telescope (HST) under the Director's Discretionary program ULLYSES. Using the medium-resolution spectrograph X-shooter, spectra of 235 OB and Wolf-Rayet (WR) stars in subsolar metallicity environments have been secured. The bulk of the targets belong to the Large and Small Magellanic Clouds, with the exception of three stars in NGC 3109 and Sextans A. <BR /> Aims: This second paper in the series focuses on the optical observations of Magellanic Clouds targets. It describes the uniform reduction of the UVB (300-560 nm) and VIS (550-1020 nm) XShootU data as well as the preparation of advanced data products that are suitable for homogeneous scientific analyses. <BR /> Methods: The data reduction of the RAW data is based on the ESO CPL X-shooter pipeline. We paid particular attention to the determination of the response curves. This required equal flat-fielding of the science and flux standard star data and the derivation of improved flux standard models. The pipeline products were then processed with our own set of routines to produce a series of advanced data products. In particular, we implemented slit-loss correction, absolute flux calibration, (semi-)automatic rectification to the continuum, and a correction for telluric lines. The spectra of individual epochs were further corrected for the barycentric motion, re-sampled and co-added, and the spectra from the two arms were merged into a single flux-calibrated spectrum covering the entire optical range with maximum signal-to-noise ratio. <BR /> Results: We identify and describe an undocumented recurrent ghost visible on the RAW data. We present an improved flat-fielding strategy that limits artifacts when the SCIENCE and FLUX standard stars are observed on different nights. The improved FLUX standard models and the new grid of anchor points limit artifacts of the response curve correction, for example on the shape of the wings of the Balmer lines, from a couple of per cent of the continuum level to less than 0.5%. We confirm the presence of a radial velocity shift of about 3.5 km s<SUP>−1</SUP> between the UVB and the VIS arm of X-shooter and that there are no short term variations impacting the RV measurements. RV precision better than 1 km s<SUP>-1</SUP> can be obtained on sharp telluric lines while RV precision on the order of 2 to 3 km s<SUP>-1</SUP> is obtained on data with the best S/N. <BR /> Conclusions: For each target observed by XShootU, we provide three types of data products: (i) two-dimensional spectra for each UVB and VIS exposure before and after correction for the instrument response; (ii) one-dimensional UVB and VIS spectra as produced by the X-shooter pipeline before and after response-correction, and applying various processing, including absolute flux calibration, telluric removal, normalization and barycentric correction; and (iii) co-added flux-calibrated and rectified spectra over the full optical range, for which all available XShootU exposures were combined. For the large majority of the targets, the final signal-to-noise ratio per resolution element is above 200 in the UVB and in the VIS co-added spectra. The reduced data and advanced scientific data products are made available to the community. Together with the HST UV ULLYSES data, they should enable various science goals, from detailed stellar atmosphere and stellar wind studies, and empirical libraries for population synthesis, to the study of the local nebular environment and feedback of massive stars in subsolar metallicity environments. <P />Full Tables 1, 2 and C.1 are available at the CDS via anonymous ftp to <A href=https://cdsarc.cds.unistra.fr>cdsarc.cds.unistra.fr</A> (ftp://130.79.128.5) or via <A href=https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/688/A104>https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/688/A104</A> <P />The DR1 data and an accompanying release documentation are made available on Zenodo <A href=https://doi.org/10.5281/zenodo.11122188>https://doi.org/10.5281/zenodo.11122188</A> <P />Based on observations collected at the European Southern Observatory under ESO program ID 106.211Z.001.
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X-Shooting ULLYSES: Massive stars at low metallicity. II. DR1: Advanced optical data products for the Magellanic CloudsContext. The XShootU project aims to obtain ground-based optical to near-infrared spectroscopy of all targets observed by the Hubble Space Telescope (HST) under the Director's Discretionary program ULLYSES. Using the medium-resolution spectrograph X-shooter, spectra of 235 OB and Wolf-Rayet (WR) stars in subsolar metallicity environments have been secured. The bulk of the targets belong to the Large and Small Magellanic Clouds, with the exception of three stars in NGC 3109 and Sextans A. <BR /> Aims: This second paper in the series focuses on the optical observations of Magellanic Clouds targets. It describes the uniform reduction of the UVB (300-560 nm) and VIS (550-1020 nm) XShootU data as well as the preparation of advanced data products that are suitable for homogeneous scientific analyses. <BR /> Methods: The data reduction of the RAW data is based on the ESO CPL X-shooter pipeline. We paid particular attention to the determination of the response curves. This required equal flat-fielding of the science and flux standard star data and the derivation of improved flux standard models. The pipeline products were then processed with our own set of routines to produce a series of advanced data products. In particular, we implemented slit-loss correction, absolute flux calibration, (semi-)automatic rectification to the continuum, and a correction for telluric lines. The spectra of individual epochs were further corrected for the barycentric motion, re-sampled and co-added, and the spectra from the two arms were merged into a single flux-calibrated spectrum covering the entire optical range with maximum signal-to-noise ratio. <BR /> Results: We identify and describe an undocumented recurrent ghost visible on the RAW data. We present an improved flat-fielding strategy that limits artifacts when the SCIENCE and FLUX standard stars are observed on different nights. The improved FLUX standard models and the new grid of anchor points limit artifacts of the response curve correction, for example on the shape of the wings of the Balmer lines, from a couple of per cent of the continuum level to less than 0.5%. We confirm the presence of a radial velocity shift of about 3.5 km s<SUP>−1</SUP> between the UVB and the VIS arm of X-shooter and that there are no short term variations impacting the RV measurements. RV precision better than 1 km s<SUP>-1</SUP> can be obtained on sharp telluric lines while RV precision on the order of 2 to 3 km s<SUP>-1</SUP> is obtained on data with the best S/N. <BR /> Conclusions: For each target observed by XShootU, we provide three types of data products: (i) two-dimensional spectra for each UVB and VIS exposure before and after correction for the instrument response; (ii) one-dimensional UVB and VIS spectra as produced by the X-shooter pipeline before and after response-correction, and applying various processing, including absolute flux calibration, telluric removal, normalization and barycentric correction; and (iii) co-added flux-calibrated and rectified spectra over the full optical range, for which all available XShootU exposures were combined. For the large majority of the targets, the final signal-to-noise ratio per resolution element is above 200 in the UVB and in the VIS co-added spectra. The reduced data and advanced scientific data products are made available to the community. Together with the HST UV ULLYSES data, they should enable various science goals, from detailed stellar atmosphere and stellar wind studies, and empirical libraries for population synthesis, to the study of the local nebular environment and feedback of massive stars in subsolar metallicity environments. <P />Full Tables 1, 2 and C.1 are available at the CDS via anonymous ftp to <A href=https://cdsarc.cds.unistra.fr>cdsarc.cds.unistra.fr</A> (ftp://130.79.128.5) or via <A href=https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/688/A104>https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/688/A104</A> <P />The DR1 data and an accompanying release documentation are made available on Zenodo <A href=https://doi.org/10.5281/zenodo.11122188>https://doi.org/10.5281/zenodo.11122188</A> <P />Based on observations collected at the European Southern Observatory under ESO program ID 106.211Z.001.
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X-Shooting ULLYSES: Massive stars at low metallicity. II. DR1: Advanced optical data products for the Magellanic CloudsContext. The XShootU project aims to obtain ground-based optical to near-infrared spectroscopy of all targets observed by the Hubble Space Telescope (HST) under the Director's Discretionary program ULLYSES. Using the medium-resolution spectrograph X-shooter, spectra of 235 OB and Wolf-Rayet (WR) stars in subsolar metallicity environments have been secured. The bulk of the targets belong to the Large and Small Magellanic Clouds, with the exception of three stars in NGC 3109 and Sextans A. <BR /> Aims: This second paper in the series focuses on the optical observations of Magellanic Clouds targets. It describes the uniform reduction of the UVB (300-560 nm) and VIS (550-1020 nm) XShootU data as well as the preparation of advanced data products that are suitable for homogeneous scientific analyses. <BR /> Methods: The data reduction of the RAW data is based on the ESO CPL X-shooter pipeline. We paid particular attention to the determination of the response curves. This required equal flat-fielding of the science and flux standard star data and the derivation of improved flux standard models. The pipeline products were then processed with our own set of routines to produce a series of advanced data products. In particular, we implemented slit-loss correction, absolute flux calibration, (semi-)automatic rectification to the continuum, and a correction for telluric lines. The spectra of individual epochs were further corrected for the barycentric motion, re-sampled and co-added, and the spectra from the two arms were merged into a single flux-calibrated spectrum covering the entire optical range with maximum signal-to-noise ratio. <BR /> Results: We identify and describe an undocumented recurrent ghost visible on the RAW data. We present an improved flat-fielding strategy that limits artifacts when the SCIENCE and FLUX standard stars are observed on different nights. The improved FLUX standard models and the new grid of anchor points limit artifacts of the response curve correction, for example on the shape of the wings of the Balmer lines, from a couple of per cent of the continuum level to less than 0.5%. We confirm the presence of a radial velocity shift of about 3.5 km s<SUP>−1</SUP> between the UVB and the VIS arm of X-shooter and that there are no short term variations impacting the RV measurements. RV precision better than 1 km s<SUP>-1</SUP> can be obtained on sharp telluric lines while RV precision on the order of 2 to 3 km s<SUP>-1</SUP> is obtained on data with the best S/N. <BR /> Conclusions: For each target observed by XShootU, we provide three types of data products: (i) two-dimensional spectra for each UVB and VIS exposure before and after correction for the instrument response; (ii) one-dimensional UVB and VIS spectra as produced by the X-shooter pipeline before and after response-correction, and applying various processing, including absolute flux calibration, telluric removal, normalization and barycentric correction; and (iii) co-added flux-calibrated and rectified spectra over the full optical range, for which all available XShootU exposures were combined. For the large majority of the targets, the final signal-to-noise ratio per resolution element is above 200 in the UVB and in the VIS co-added spectra. The reduced data and advanced scientific data products are made available to the community. Together with the HST UV ULLYSES data, they should enable various science goals, from detailed stellar atmosphere and stellar wind studies, and empirical libraries for population synthesis, to the study of the local nebular environment and feedback of massive stars in subsolar metallicity environments. <P />Full Tables 1, 2 and C.1 are available at the CDS via anonymous ftp to <A href=https://cdsarc.cds.unistra.fr>cdsarc.cds.unistra.fr</A> (ftp://130.79.128.5) or via <A href=https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/688/A104>https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/688/A104</A> <P />The DR1 data and an accompanying release documentation are made available on Zenodo <A href=https://doi.org/10.5281/zenodo.11122188>https://doi.org/10.5281/zenodo.11122188</A> <P />Based on observations collected at the European Southern Observatory under ESO program ID 106.211Z.001.
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X-Shooting ULLYSES: Massive stars at low metallicity. III. Terminal wind speeds of ULLYSES massive starsContext. The winds of massive stars have a significant impact on stellar evolution and on the surrounding medium. The maximum speed reached by these outflows, the terminal wind speed v<SUB>∞</SUB>, is a global wind parameter and an essential input for models of stellar atmospheres and feedback. With the arrival of the ULLYSES programme, a legacy UV spectroscopic survey with the Hubble Space Telescope, we have the opportunity to quantify the wind speeds of massive stars at sub-solar metallicity (in the Large and Small Magellanic Clouds, 0.5 Z<SUB>⊙</SUB> and 0.2 Z<SUB>⊙</SUB>, respectively) at an unprecedented scale. <BR /> Aims: We empirically quantify the wind speeds of a large sample of OB stars, including supergiants, giants, and dwarfs at sub-solar metallicity. Using these measurements, we investigate trends of v<SUB>∞</SUB> with a number of fundamental stellar parameters, namely effective temperature (T<SUB>eff</SUB>), metallicity (Z), and surface escape velocity v<SUB>esc</SUB>. <BR /> Methods: We empirically determined v<SUB>∞</SUB> for a sample of 149 OB stars in the Magellanic Clouds either by directly measuring the maximum velocity shift of the absorption component of the C IV λλ1548-1550 line profile, or by fitting synthetic spectra produced using the Sobolev with exact integration method. Stellar parameters were either collected from the literature, obtained using spectral-type calibrations, or predicted from evolutionary models. <BR /> Results: We find strong trends of v<SUB>∞</SUB> with T<SUB>eff</SUB> and v<SUB>esc</SUB> when the wind is strong enough to cause a saturated P Cygni profile in C IV λλ1548-1550. We find evidence for a metallicity dependence on the terminal wind speed v<SUB>∞</SUB> ∝ Z<SUP>0.22±0.03</SUP> when we compared our results to previous Galactic studies. <BR /> Conclusions: Our results suggest that T<SUB>eff</SUB> rather than v<SUB>esc</SUB> should be used as a straightforward empirical prediction of v<SUB>∞</SUB> and that the observed Z dependence is steeper than suggested by earlier works.
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X-Shooting ULLYSES: Massive stars at low metallicity. III. Terminal wind speeds of ULLYSES massive starsContext. The winds of massive stars have a significant impact on stellar evolution and on the surrounding medium. The maximum speed reached by these outflows, the terminal wind speed v<SUB>∞</SUB>, is a global wind parameter and an essential input for models of stellar atmospheres and feedback. With the arrival of the ULLYSES programme, a legacy UV spectroscopic survey with the Hubble Space Telescope, we have the opportunity to quantify the wind speeds of massive stars at sub-solar metallicity (in the Large and Small Magellanic Clouds, 0.5 Z<SUB>⊙</SUB> and 0.2 Z<SUB>⊙</SUB>, respectively) at an unprecedented scale. <BR /> Aims: We empirically quantify the wind speeds of a large sample of OB stars, including supergiants, giants, and dwarfs at sub-solar metallicity. Using these measurements, we investigate trends of v<SUB>∞</SUB> with a number of fundamental stellar parameters, namely effective temperature (T<SUB>eff</SUB>), metallicity (Z), and surface escape velocity v<SUB>esc</SUB>. <BR /> Methods: We empirically determined v<SUB>∞</SUB> for a sample of 149 OB stars in the Magellanic Clouds either by directly measuring the maximum velocity shift of the absorption component of the C IV λλ1548-1550 line profile, or by fitting synthetic spectra produced using the Sobolev with exact integration method. Stellar parameters were either collected from the literature, obtained using spectral-type calibrations, or predicted from evolutionary models. <BR /> Results: We find strong trends of v<SUB>∞</SUB> with T<SUB>eff</SUB> and v<SUB>esc</SUB> when the wind is strong enough to cause a saturated P Cygni profile in C IV λλ1548-1550. We find evidence for a metallicity dependence on the terminal wind speed v<SUB>∞</SUB> ∝ Z<SUP>0.22±0.03</SUP> when we compared our results to previous Galactic studies. <BR /> Conclusions: Our results suggest that T<SUB>eff</SUB> rather than v<SUB>esc</SUB> should be used as a straightforward empirical prediction of v<SUB>∞</SUB> and that the observed Z dependence is steeper than suggested by earlier works.
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TOI-2447 b / NGTS-29 b: a 69-day Saturn around a Solar analogueDiscovering transiting exoplanets with relatively long orbital periods (>10 d) is crucial to facilitate the study of cool exoplanet atmospheres (T<SUB>eq</SUB> < 700 K) and to understand exoplanet formation and inward migration further out than typical transiting exoplanets. In order to discover these longer period transiting exoplanets, long-term photometric, and radial velocity campaigns are required. We report the discovery of TOI-2447 b (=NGTS-29 b), a Saturn-mass transiting exoplanet orbiting a bright (T = 10.0) Solar-type star (T<SUB>eff</SUB> = 5730 K). TOI-2447 b was identified as a transiting exoplanet candidate from a single transit event of 1.3 per cent depth and 7.29 h duration in TESS Sector 31 and a prior transit event from 2017 in NGTS data. Four further transit events were observed with NGTS photometry which revealed an orbital period of P = 69.34 d. The transit events establish a radius for TOI-2447 b of $0.865 \pm 0.010\, \rm R_{\rm J}$, while radial velocity measurements give a mass of $0.386 \pm 0.025\, \rm M_{\rm J}$. The equilibrium temperature of the planet is 414 K, making it much cooler than the majority of TESS planet discoveries. We also detect a transit signal in NGTS data not caused by TOI-2447 b, along with transit timing variations and evidence for a ~150 d signal in radial velocity measurements. It is likely that the system hosts additional planets, but further photometry and radial velocity campaigns will be needed to determine their parameters with confidence. TOI-2447 b/NGTS-29 b joins a small but growing population of cool giants that will provide crucial insights into giant planet composition and formation mechanisms.
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TOI-2490b - the most eccentric brown dwarf transiting in the brown dwarf desertWe report the discovery of the most eccentric transiting brown dwarf in the brown dwarf desert, TOI-2490b. The brown dwarf desert is the lack of brown dwarfs around main-sequence stars within <inline-formula><tex-math id=TM0001 notation=LaTeX>$\sim 3$</tex-math></inline-formula> au and is thought to be caused by differences in formation mechanisms between a star and planet. To date, only <inline-formula><tex-math id=TM0002 notation=LaTeX>$\sim 40$</tex-math></inline-formula> transiting brown dwarfs have been confirmed. TOI-2490b is a <inline-formula><tex-math id=TM0003 notation=LaTeX>$73.6\pm 2.4$</tex-math></inline-formula> <inline-formula><tex-math id=TM0004 notation=LaTeX>$M_{\rm J}$</tex-math></inline-formula>, <inline-formula><tex-math id=TM0005 notation=LaTeX>$1.00\pm 0.02$</tex-math></inline-formula> <inline-formula><tex-math id=TM0006 notation=LaTeX>$R_{\rm J}$</tex-math></inline-formula> brown dwarf orbiting a <inline-formula><tex-math id=TM0007 notation=LaTeX>$1.004_{-0.022}^{+0.031}$</tex-math></inline-formula> <inline-formula><tex-math id=TM0008 notation=LaTeX>${\rm M}_{\odot }$</tex-math></inline-formula>, <inline-formula><tex-math id=TM0009 notation=LaTeX>$1.105_{-0.012}^{+0.012}$</tex-math></inline-formula> <inline-formula><tex-math id=TM0010 notation=LaTeX>${\rm R}_{\odot }$</tex-math></inline-formula> sun-like star on a 60.33 d orbit with an eccentricity of <inline-formula><tex-math id=TM0011 notation=LaTeX>$0.77989\pm 0.00049$</tex-math></inline-formula>. The discovery was detected within Transiting Exoplanet Survey Satellite sectors 5 (30 min cadence) and 32 (2 min and 20 s cadence). It was then confirmed with 31 radial velocity measurements with FEROS by the WINE collaboration and photometric observations with the Next Generation Transit Survey. Stellar modelling of the host star estimates an age of <inline-formula><tex-math id=TM0012 notation=LaTeX>$\sim 8$</tex-math></inline-formula> Gyr, which is supported by estimations from kinematics likely placing the object within the thin disc. However, this is not consistent with model brown dwarf isochrones for the system age suggesting an inflated radius. Only one other transiting brown dwarf with an eccentricity higher than 0.6 is currently known in the brown dwarf desert. Demographic studies of brown dwarfs have suggested such high eccentricity is indicative of stellar formation mechanisms.
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TOI-2490b - the most eccentric brown dwarf transiting in the brown dwarf desertWe report the discovery of the most eccentric transiting brown dwarf in the brown dwarf desert, TOI-2490b. The brown dwarf desert is the lack of brown dwarfs around main-sequence stars within <inline-formula><tex-math id=TM0001 notation=LaTeX>$\sim 3$</tex-math></inline-formula> au and is thought to be caused by differences in formation mechanisms between a star and planet. To date, only <inline-formula><tex-math id=TM0002 notation=LaTeX>$\sim 40$</tex-math></inline-formula> transiting brown dwarfs have been confirmed. TOI-2490b is a <inline-formula><tex-math id=TM0003 notation=LaTeX>$73.6\pm 2.4$</tex-math></inline-formula> <inline-formula><tex-math id=TM0004 notation=LaTeX>$M_{\rm J}$</tex-math></inline-formula>, <inline-formula><tex-math id=TM0005 notation=LaTeX>$1.00\pm 0.02$</tex-math></inline-formula> <inline-formula><tex-math id=TM0006 notation=LaTeX>$R_{\rm J}$</tex-math></inline-formula> brown dwarf orbiting a <inline-formula><tex-math id=TM0007 notation=LaTeX>$1.004_{-0.022}^{+0.031}$</tex-math></inline-formula> <inline-formula><tex-math id=TM0008 notation=LaTeX>${\rm M}_{\odot }$</tex-math></inline-formula>, <inline-formula><tex-math id=TM0009 notation=LaTeX>$1.105_{-0.012}^{+0.012}$</tex-math></inline-formula> <inline-formula><tex-math id=TM0010 notation=LaTeX>${\rm R}_{\odot }$</tex-math></inline-formula> sun-like star on a 60.33 d orbit with an eccentricity of <inline-formula><tex-math id=TM0011 notation=LaTeX>$0.77989\pm 0.00049$</tex-math></inline-formula>. The discovery was detected within Transiting Exoplanet Survey Satellite sectors 5 (30 min cadence) and 32 (2 min and 20 s cadence). It was then confirmed with 31 radial velocity measurements with FEROS by the WINE collaboration and photometric observations with the Next Generation Transit Survey. Stellar modelling of the host star estimates an age of <inline-formula><tex-math id=TM0012 notation=LaTeX>$\sim 8$</tex-math></inline-formula> Gyr, which is supported by estimations from kinematics likely placing the object within the thin disc. However, this is not consistent with model brown dwarf isochrones for the system age suggesting an inflated radius. Only one other transiting brown dwarf with an eccentricity higher than 0.6 is currently known in the brown dwarf desert. Demographic studies of brown dwarfs have suggested such high eccentricity is indicative of stellar formation mechanisms.
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X-Shooting ULLYSES: Massive stars at low metallicity: IV. Spectral analysis methods and exemplary results for O starsContext. The spectral analysis of hot, massive stars is a fundamental astrophysical method of determining their intrinsic properties and feedback. With their inherent, radiation-driven winds, the quantitative spectroscopy for hot, massive stars requires detailed numerical modeling of the atmosphere and an iterative treatment in order to obtain the best solution within a given framework. Aims. We present an overview of different techniques for the quantitative spectroscopy of hot stars employed within the X-Shooting ULLYSES collaboration, ranging from grid-based approaches to tailored spectral fits. By performing a blind test for selected targets, we gain an overview of the similarities and differences between the resulting stellar and wind parameters. Our study is not a systematic benchmark between different codes or methods; our aim is to provide an overview of the parameter spread caused by different approaches. Methods. For three different stars from the XShooting ULLYSES sample (SMC O5 star AzV 377, LMC O7 star Sk -69° 50, and LMC O9 star Sk-66° 171), we employ different stellar atmosphere codes (CMFGEN, FASTWIND, PoWR) and different strategies to determine their best-fitting model solutions. For our analyses, UV and optical spectroscopy are used to derive the stellar and wind properties with some methods relying purely on optical data for comparison. To determine the overall spectral energy distribution, we further employ additional photometry from the literature. Results. The effective temperatures found for each of the three different sample stars agree within 3 kK, while the differences in log g can be up to 0.2 dex. Luminosity differences of up to 0.1 dex result from different reddening assumptions, which seem to be systematically larger for the methods employing a genetic algorithm. All sample stars are found to be enriched in nitrogen. The terminal wind velocities are surprisingly similar and do not strictly follow the u<SUB>∞</SUB>‑T<SUB>eff</SUB> relation. Conclusions. We find reasonable agreement in terms of the derived stellar and wind parameters between the different methods. Tailored fitting methods tend to be able to minimize or avoid discrepancies obtained with coarser or increasingly automatized treatments. The inclusion of UV spectral data is essential for the determination of realistic wind parameters. For one target (Sk -69° 50), we find clear indications of an evolved status.
