AOP Open Repository: Recent submissions
Now showing items 1-20 of 1003
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The HASHTAG project II. Giant molecular cloud properties across the M31 discWe present a study of giant molecular cloud (GMC) properties in the Andromeda galaxy (M31) using CO(3-2) data from the James Clerk Maxwell Telescope (JCMT) in selected regions across the disc and in the nuclear ring, and comparing them with CO(1-0) observations from the IRAM 30m telescope in the same regions. We find that GMCs in the centre of M31 generally exhibit larger velocity dispersions (σ) and sizes (R) compared to those in the disc, while their average surface density (Σ) and turbulent pressure (P<SUB>turb</SUB>) are lower. This low turbulent pressure in the central region is primarily due to the low density of molecular gas. The estimated GMC properties depend on the choice of CO transitions. Compared to CO(1-0), CO(3-2) exhibits smaller velocity dispersion and equivalent radius but higher surface density. These differences highlight the distinct physical conditions probed by different molecular gas tracers. We estimate the virial parameter α<SUB>vir</SUB>∝σ<SUP>2</SUP>R/Σ and find that most molecular clouds exhibit high values (α<SUB>vir</SUB> ~ 4 - 6) for both CO transitions, indicating that they are unbound. Furthermore, clouds in the nuclear ring display even larger α<SUB>vir</SUB> values of ≲ 100, suggesting that they may be highly dynamic, short-lived structures, although they could potentially achieve equilibrium under the external pressure exerted by the surrounding interstellar medium.
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PAMS: The Perseus Arm Molecular Survey-I. Survey description and first resultsThe external environments surrounding molecular clouds vary widely across galaxies such as the Milky Way, and statistical samples of clouds are required to understand them. We present the Perseus Arm Molecular Survey (PAMS), a James Clerk Maxwell Telescope (JCMT) survey combining new and archival data of molecular-cloud complexes in the outer Perseus spiral arm in <inline-formula><tex-math id=TM0001 notation=LaTeX>$^{12}$</tex-math></inline-formula>CO, <inline-formula><tex-math id=TM0002 notation=LaTeX>$^{13}$</tex-math></inline-formula>CO, and C<inline-formula><tex-math id=TM0003 notation=LaTeX>$^{18}$</tex-math></inline-formula>O (J = 3-2). With a survey area of <inline-formula><tex-math id=TM0005 notation=LaTeX>$\sim$</tex-math></inline-formula>8 deg<inline-formula><tex-math id=TM0006 notation=LaTeX>$^2$</tex-math></inline-formula>, PAMS covers well-known complexes such as W3, W5, and NGC 7538 with two fields at <inline-formula><tex-math id=TM0007 notation=LaTeX>$\ell \approx 110^{\circ }$</tex-math></inline-formula> and <inline-formula><tex-math id=TM0008 notation=LaTeX>$\ell \approx 135^{\circ }$</tex-math></inline-formula>. PAMS has an effective resolution of 17 arcsec, and rms sensitivity of <inline-formula><tex-math id=TM0009 notation=LaTeX>$T_\mathrm{mb}= 0.7$</tex-math></inline-formula>-1.0 K in 0.3 km s<inline-formula><tex-math id=TM0010 notation=LaTeX>$^{-1}$</tex-math></inline-formula> channels. Here we present a first look at the data, and compare the PAMS regions in the Outer Galaxy with Inner Galaxy regions from the CO Heterodyne Inner Milky Way Plane Survey (CHIMPS). By comparing the various CO data with maps of H<inline-formula><tex-math id=TM0011 notation=LaTeX>$_2$</tex-math></inline-formula> column density from Herschel, we calculate representative values for the CO-to-H<inline-formula><tex-math id=TM0012 notation=LaTeX>$_2$</tex-math></inline-formula> column-density X-factors, which are <inline-formula><tex-math id=TM0014 notation=LaTeX>$X_\mathrm{^{12}CO\, (3-2)}$</tex-math></inline-formula><inline-formula><tex-math id=TM0015 notation=LaTeX>$\, =4.0\times 10^{20}$</tex-math></inline-formula> and <inline-formula><tex-math id=TM0016 notation=LaTeX>$X_\mathrm{^{13}CO\, (3-2)}$</tex-math></inline-formula><inline-formula><tex-math id=TM0017 notation=LaTeX>$\, =4.0\times 10^{21}$</tex-math></inline-formula> cm<inline-formula><tex-math id=TM0018 notation=LaTeX>$^{-2}$</tex-math></inline-formula> (K km s<inline-formula><tex-math id=TM0019 notation=LaTeX>$^{-1}$</tex-math></inline-formula>)<inline-formula><tex-math id=TM0020 notation=LaTeX>$^{-1}$</tex-math></inline-formula> with a factor of 1.5 uncertainty. We find that the emission profiles, size-linewidth, and mass-radius relationships of <inline-formula><tex-math id=TM0021 notation=LaTeX>$^{13}$</tex-math></inline-formula>CO-traced structures are similar between the Inner and Outer Galaxy. Although PAMS sources are slightly more massive than their Inner Galaxy counterparts for a given size scale, the discrepancy can be accounted for by the Galactic gradient in gas-to-dust mass ratio, uncertainties in the X-factors, and selection biases. We have made the PAMS data publicly available, complementing other CO surveys targeting different regions of the Galaxy in different isotopologues and transitions.
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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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Linear and non-linear models for large-amplitude radial pulsation in faint blue stars (BLAPs)The recent discovery of large-amplitude pulsations in faint blue stars (BLAPs) provides both challenges for stellar pulsation theory and opportunities to explore the late evolution of low-mass stars. This paper explores the radial-mode stability of stars across parameter space occupied by BLAPs. Models are constructed for homogeneous stellar envelopes and are agnostic of evolution. Linear non-adiabatic models demonstrate the major requirement for pulsations to be enrichment of iron and nickel in the driving zone to a few times the solar abundance. There is no constraint on mass. Non-linear models demonstrate that BLAP pulsations will be of large amplitude and will show strong shocks at minimum radius. A variety of light-curve shapes are found across the BLAP instability strip, accounting for the variety observed. Linearised period relations are derived from the non-linear models. The phase of maximum luminosity relative to minimum radius is correlated with effective temperature ( T<SUB>eff</SUB>), preceding for cool stars and following for hot stars, and split if close to minimum radius. In both linear and non-linear cases, most models pulsate in the fundamental mode (F). First-overtone (1H) pulsations are excited on the low luminosity blue side of the instability region and become more prevalent at higher mass. The period ratio P<SUB>1H</SUB>/P<SUB>F</SUB> = 0.81 contrasts with the classical Cepheid value (0.70 - 0.75). The transition from F to 1H mode pulsations follows a period-mass relation; the F-mode pulsators adjacent to the transition show a reverse shock. At high T<SUB>eff</SUB> some non-linear models show unstable overtone modes up to 5H and multi-mode behaviour. The linear and non-linear analyses concur on the red-edge of the instability region, but the non-linear blue edge is hotter.
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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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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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Discovery of Metal-poor and Distant Pre–Main Sequence Candidates in WLM with JWSTWe present the discovery of 12 metal-poor and distant pre–main sequence (PMS) candidates in the dwarf irregular galaxy Wolf–Lundmark–Melotte ∼968 kpc away, at a present-day metallicity of [Fe/H] ∼ –0.9. These candidates have masses between 1.25 and 5 M<SUB>⊙</SUB>, with ages <10 Myr, and exhibit significant near-infrared excesses at 2.5 and 4.3 μm. They are concentrated within a cluster roughly 10 pc (2″) across, situated in the H II region [HM95]-9. These are the most distant and metal-poor PMS stars known, and they can offer new quantitative insights into star formation at low metallicities.
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X-Shooting ULLYSES: Massive stars at low metallicity: X. Physical parameters and feedback of massive stars in the LMC N11 B star-forming regionMassive stars drive the ionization and mechanical feedback within young star-forming regions. The Large Magellanic Cloud (LMC) is an ideal galaxy for studying individual massive stars and quantifying their feedback contribution to the environment. We analyze eight exemplary targets in LMC N11 B from the Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) program using novel spectra from HST (COS and STIS) in the UV, and from VLT (X-shooter) in the optical. We model the spectra of early to late O-type stars using state-of-the-art PoWR atmosphere models. We determine the stellar and wind parameters (e.g., T<SUB>⋆</SUB>, log g, L<SUB>⋆</SUB>, Ṁ, and v<SUB>∞</SUB>) of the analyzed objects, chemical abundances (C, N, and O), ionizing and mechanical feedback (Q<SUB>H</SUB>, Q<SUB>HeI</SUB>, Q<SUB>He II</SUB>, and L<SUB>mec</SUB>), and X-rays. We report ages of 2–4.5 Myr and masses of 30–60 M<SUB>⊙</SUB> for the analyzed stars in N11 B, which are consistent with a scenario of sequential star formation. We note that the observed wind-momentum–luminosity relation is consistent with theoretical predictions. We detect nitrogen enrichment by up to a factor of seven in most of the stars. However, we do not find a correlation between nitrogen enrichment and projected rotational velocity. Finally, based on their spectral type, we estimate the total ionizing photons injected from the O-type stars in N11 B into its environment. We report log (Σ Q<SUB>H</SUB>) = 50.5 ph s<SUP>‑1</SUP>, log (Σ Q<SUB>He I</SUB>) = 49.6 ph s<SUP>‑1</SUP>, and log (Σ Q<SUB>He II</SUB>)= 44.4 ph s<SUP>‑1</SUP>, consistent with the total ionizing budget in N11.
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Discovery of Metal-poor and Distant Pre–Main Sequence Candidates in WLM with JWSTWe present the discovery of 12 metal-poor and distant pre–main sequence (PMS) candidates in the dwarf irregular galaxy Wolf–Lundmark–Melotte ∼968 kpc away, at a present-day metallicity of [Fe/H] ∼ –0.9. These candidates have masses between 1.25 and 5 M<SUB>⊙</SUB>, with ages <10 Myr, and exhibit significant near-infrared excesses at 2.5 and 4.3 μm. They are concentrated within a cluster roughly 10 pc (2″) across, situated in the H II region [HM95]-9. These are the most distant and metal-poor PMS stars known, and they can offer new quantitative insights into star formation at low metallicities.
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Optical evolution of AT 2024wpp: the high-velocity outflows in Cow-like transients are consistent with high spherical symmetryWe present the analysis of optical/near-infrared (NIR) data and host galaxy properties of a bright, extremely rapidly evolving transient, AT 2024wpp, which resembles the enigmatic AT 2018cow. AT 2024wpp rose to a peak brightness of <inline-formula><tex-math id=TM0001 notation=LaTeX>$c=-21.9$</tex-math></inline-formula> mag in 4.3 d and remained above the half-maximum brightness for only 6.7 d. The blackbody fits to the photometry show that the event remained persistently hot (<inline-formula><tex-math id=TM0002 notation=LaTeX>$T\gtrsim 20\, 000$</tex-math></inline-formula> K) with a rapidly receding photosphere (<inline-formula><tex-math id=TM0003 notation=LaTeX>$v\sim 11\, 500$</tex-math></inline-formula> km s<inline-formula><tex-math id=TM0004 notation=LaTeX>$^{-1}$</tex-math></inline-formula>), similarly to AT 2018cow albeit with a several times larger photosphere. <inline-formula><tex-math id=TM0005 notation=LaTeX>$JH$</tex-math></inline-formula> photometry reveals an NIR excess over the thermal emission at <inline-formula><tex-math id=TM0006 notation=LaTeX>$\sim +20$</tex-math></inline-formula> d, indicating a presence of an additional component. The spectra are consistent with blackbody emission throughout our spectral sequence ending at <inline-formula><tex-math id=TM0007 notation=LaTeX>$+21.9$</tex-math></inline-formula> d, showing a tentative, very broad emission feature at <inline-formula><tex-math id=TM0008 notation=LaTeX>$\sim 5500$</tex-math></inline-formula> Å - implying that the optical photosphere is likely within a near-relativistic outflow. Furthermore, reports of strong X-ray and radio emission cement the nature of AT 2024wpp as a likely Cow-like transient. AT 2024wpp is the second event of the class with optical polarimetry. Our <inline-formula><tex-math id=TM0009 notation=LaTeX>$BVRI$</tex-math></inline-formula> observations obtained from <inline-formula><tex-math id=TM0010 notation=LaTeX>$+6.1$</tex-math></inline-formula> to <inline-formula><tex-math id=TM0011 notation=LaTeX>$+14.4$</tex-math></inline-formula> d show a low polarization of <inline-formula><tex-math id=TM0012 notation=LaTeX>$P\lesssim 0.5$</tex-math></inline-formula> per cent across all bands, similar to AT 2018cow that was consistent with <inline-formula><tex-math id=TM0013 notation=LaTeX>$P\sim 0$</tex-math></inline-formula> per cent during the same outflow-driven phase. In the absence of evidence for a preferential viewing angle, it is unlikely that both events would have shown low polarization in the case that their photospheres were aspherical. As such, we conclude that the near-relativistic outflows launched in these events are likely highly spherical, but polarimetric observations of further events are crucial to constrain their ejecta geometry and stratification in detail.
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X-Shooting ULLYSES: Massive stars at low metallicity: X. Physical parameters and feedback of massive stars in the LMC N11 B star-forming regionMassive stars drive the ionization and mechanical feedback within young star-forming regions. The Large Magellanic Cloud (LMC) is an ideal galaxy for studying individual massive stars and quantifying their feedback contribution to the environment. We analyze eight exemplary targets in LMC N11 B from the Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) program using novel spectra from HST (COS and STIS) in the UV, and from VLT (X-shooter) in the optical. We model the spectra of early to late O-type stars using state-of-the-art PoWR atmosphere models. We determine the stellar and wind parameters (e.g., T<SUB>⋆</SUB>, log g, L<SUB>⋆</SUB>, Ṁ, and v<SUB>∞</SUB>) of the analyzed objects, chemical abundances (C, N, and O), ionizing and mechanical feedback (Q<SUB>H</SUB>, Q<SUB>HeI</SUB>, Q<SUB>He II</SUB>, and L<SUB>mec</SUB>), and X-rays. We report ages of 2–4.5 Myr and masses of 30–60 M<SUB>⊙</SUB> for the analyzed stars in N11 B, which are consistent with a scenario of sequential star formation. We note that the observed wind-momentum–luminosity relation is consistent with theoretical predictions. We detect nitrogen enrichment by up to a factor of seven in most of the stars. However, we do not find a correlation between nitrogen enrichment and projected rotational velocity. Finally, based on their spectral type, we estimate the total ionizing photons injected from the O-type stars in N11 B into its environment. We report log (Σ Q<SUB>H</SUB>) = 50.5 ph s<SUP>‑1</SUP>, log (Σ Q<SUB>He I</SUB>) = 49.6 ph s<SUP>‑1</SUP>, and log (Σ Q<SUB>He II</SUB>)= 44.4 ph s<SUP>‑1</SUP>, consistent with the total ionizing budget in N11.
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Optical evolution of AT 2024wpp: the high-velocity outflows in Cow-like transients are consistent with high spherical symmetryWe present the analysis of optical/near-infrared (NIR) data and host galaxy properties of a bright, extremely rapidly evolving transient, AT 2024wpp, which resembles the enigmatic AT 2018cow. AT 2024wpp rose to a peak brightness of <inline-formula><tex-math id=TM0001 notation=LaTeX>$c=-21.9$</tex-math></inline-formula> mag in 4.3 d and remained above the half-maximum brightness for only 6.7 d. The blackbody fits to the photometry show that the event remained persistently hot (<inline-formula><tex-math id=TM0002 notation=LaTeX>$T\gtrsim 20\, 000$</tex-math></inline-formula> K) with a rapidly receding photosphere (<inline-formula><tex-math id=TM0003 notation=LaTeX>$v\sim 11\, 500$</tex-math></inline-formula> km s<inline-formula><tex-math id=TM0004 notation=LaTeX>$^{-1}$</tex-math></inline-formula>), similarly to AT 2018cow albeit with a several times larger photosphere. <inline-formula><tex-math id=TM0005 notation=LaTeX>$JH$</tex-math></inline-formula> photometry reveals an NIR excess over the thermal emission at <inline-formula><tex-math id=TM0006 notation=LaTeX>$\sim +20$</tex-math></inline-formula> d, indicating a presence of an additional component. The spectra are consistent with blackbody emission throughout our spectral sequence ending at <inline-formula><tex-math id=TM0007 notation=LaTeX>$+21.9$</tex-math></inline-formula> d, showing a tentative, very broad emission feature at <inline-formula><tex-math id=TM0008 notation=LaTeX>$\sim 5500$</tex-math></inline-formula> Å - implying that the optical photosphere is likely within a near-relativistic outflow. Furthermore, reports of strong X-ray and radio emission cement the nature of AT 2024wpp as a likely Cow-like transient. AT 2024wpp is the second event of the class with optical polarimetry. Our <inline-formula><tex-math id=TM0009 notation=LaTeX>$BVRI$</tex-math></inline-formula> observations obtained from <inline-formula><tex-math id=TM0010 notation=LaTeX>$+6.1$</tex-math></inline-formula> to <inline-formula><tex-math id=TM0011 notation=LaTeX>$+14.4$</tex-math></inline-formula> d show a low polarization of <inline-formula><tex-math id=TM0012 notation=LaTeX>$P\lesssim 0.5$</tex-math></inline-formula> per cent across all bands, similar to AT 2018cow that was consistent with <inline-formula><tex-math id=TM0013 notation=LaTeX>$P\sim 0$</tex-math></inline-formula> per cent during the same outflow-driven phase. In the absence of evidence for a preferential viewing angle, it is unlikely that both events would have shown low polarization in the case that their photospheres were aspherical. As such, we conclude that the near-relativistic outflows launched in these events are likely highly spherical, but polarimetric observations of further events are crucial to constrain their ejecta geometry and stratification in detail.
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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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Looking into the faintEst WIth MUSE (LEWIS): Exploring the nature of ultra-diffuse galaxies in the Hydra-I cluster: II. Stellar kinematics and dynamical massesContext. This paper focuses on a class of galaxies characterised by an extremely low surface brightness: ultra-diffuse galaxies (UDGs). We used new integral-field (IF) spectroscopic data, obtained with the ESO Large Programme Looking into the faintEst WIth MUSE (LEWIS). It provides the first homogeneous IF spectroscopic survey performed by MUSE at the Very Large Telescope of a complete sample of UDGs and low-surface-brightness galaxies within a virial radius of 0.4 in the Hydra I cluster, according to the UDG abundance-halo mass relation. Aims. Our main goals are addressing the possible formation channels for this class of objects and investigating possible correlations of their observational properties, including the stacked (1D) and spatially resolved (2D) stellar kinematics. In particular, we derive the stellar velocity dispersion from the stacked spectrum integrated within the effective radius (σ<SUB>eff</SUB>) and measure the velocity map of the galaxies in LEWIS. These quantities are used to estimate their dynamical mass (M<SUB>dyn</SUB>). Methods. We extracted the 1D stacked spectrum inside the effective radius (R<SUB>eff</SUB>), which guarantees a high signal-to-noise ratio, to obtain an unbiased measure of σ<SUB>eff</SUB>. To derive the spatially resolved stellar kinematics, we first applied the Voronoi tessellation algorithm to bin the spaxels in the datacube, and then we derived the stellar kinematics in each bin, following the same prescription as adopted for the 1D case. We extracted the velocity profiles along the galaxy major and minor axes and measured the semi-amplitude (ΔV) of the velocity curve. Results. We found that 7 out of 18 UDGs in LEWIS show a mild rotation (ΔV ∼ 25 ‑ 40 km s<SUP>‑1</SUP>), 5 lack evidence of any rotation, and the remaining 6 UDGs are unconstrained cases. This is the first large census of velocity profiles for UDGs. The UDGs in LEWIS are characterised by low values of σ<SUB>eff</SUB> (≤30 km s<SUP>‑1</SUP>) on average, which is comparable with available values from the literature. Two objects show higher values of σ<SUB>eff</SUB> (∼30 ‑ 40 km s<SUP>‑1</SUP>). These higher values might reasonably be due to the fast rotation observed in these galaxies, which affects the values of σ<SUB>eff</SUB>. In the Faber-Jackson relation plane, we found a group of UDGs consistent with the relation within the error bars. Outliers of the Faber-Jackson relation are objects with a non-negligible rotation component. The UDGs and LSB galaxies in the LEWIS sample have a larger dark matter (DM) content on average than dwarf galaxies (M<SUB>dyn</SUB>/L<SUB>V, eff</SUB> ∼ 10 ‑ 100 M<SUB>⊙</SUB>/L<SUB>⊙</SUB>) with a similar total luminosity. We do not find clear correlations between the derived structural properties and the local environment. Conclusions. By mapping the stellar kinematics for a homogenous sample of UDGs in a cluster environment, we found a significant rotation for many galaxies. Therefore, two classes of UDGs are found in the Hydra I cluster based on the stellar kinematics: rotating and non-rotating systems. This result, combined with the DM content and the upcoming analysis of the star formation history and globular cluster population, can help us to distinguish between the several formation scenarios proposed for UDGs.
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The PLATO field selection process: II. Characterization of LOPS2, the first long-pointing fieldPLAnetary Transits and Oscillations of stars (PLATO) is an ESA M-class mission to be launched by the end of 2026 to discover and characterize transiting planets around bright and nearby stars, and in particular habitable rocky planets hosted by solar-like stars. Over the mission lifetime, an average of 8% of the science data rate will be allocated to Guest Observer programs selected by ESA through public calls. Hence, it is essential for the community to know in advance where the observing fields will be located. In a previous paper, we identified two preliminary long-pointing fields (LOPN1 and LOPS1) for PLATO, respectively in the northern and southern hemispheres. Here we present LOPS2, a slightly adjusted version of the southern field that has recently been selected by the PLATO Science Working Team as the first field to be observed by PLATO for at least two continuous years, following the scientific requirements. In this paper, we describe the astrophysical content of LOPS2 in detail, including known planetary systems, bright stars, variables, binary stars, star clusters, and synergies with other current and future facilities.
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The PLATO field selection process: II. Characterization of LOPS2, the first long-pointing fieldPLAnetary Transits and Oscillations of stars (PLATO) is an ESA M-class mission to be launched by the end of 2026 to discover and characterize transiting planets around bright and nearby stars, and in particular habitable rocky planets hosted by solar-like stars. Over the mission lifetime, an average of 8% of the science data rate will be allocated to Guest Observer programs selected by ESA through public calls. Hence, it is essential for the community to know in advance where the observing fields will be located. In a previous paper, we identified two preliminary long-pointing fields (LOPN1 and LOPS1) for PLATO, respectively in the northern and southern hemispheres. Here we present LOPS2, a slightly adjusted version of the southern field that has recently been selected by the PLATO Science Working Team as the first field to be observed by PLATO for at least two continuous years, following the scientific requirements. In this paper, we describe the astrophysical content of LOPS2 in detail, including known planetary systems, bright stars, variables, binary stars, star clusters, and synergies with other current and future facilities.
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The PLATO field selection process: II. Characterization of LOPS2, the first long-pointing fieldPLAnetary Transits and Oscillations of stars (PLATO) is an ESA M-class mission to be launched by the end of 2026 to discover and characterize transiting planets around bright and nearby stars, and in particular habitable rocky planets hosted by solar-like stars. Over the mission lifetime, an average of 8% of the science data rate will be allocated to Guest Observer programs selected by ESA through public calls. Hence, it is essential for the community to know in advance where the observing fields will be located. In a previous paper, we identified two preliminary long-pointing fields (LOPN1 and LOPS1) for PLATO, respectively in the northern and southern hemispheres. Here we present LOPS2, a slightly adjusted version of the southern field that has recently been selected by the PLATO Science Working Team as the first field to be observed by PLATO for at least two continuous years, following the scientific requirements. In this paper, we describe the astrophysical content of LOPS2 in detail, including known planetary systems, bright stars, variables, binary stars, star clusters, and synergies with other current and future facilities.
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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.
