Astronomy & Astrophysics最新文献

{"title":"Detection of the [CI] λ8727 emission line. Low-ionization structures in NGC 7009","authors":"S. Akras, H. Monteiro, J. R. Walsh, L. Konstantinou, D.R. Gonçalves, J. Garcia--Rojas, P. Boumis, I., Aleman","doi":"10.1051/0004-6361/202450325","DOIUrl":"https://doi.org/10.1051/0004-6361/202450325","url":null,"abstract":"We report the first spatially resolved detection of the near-infrared lambda 8727 emission from the outer pair of low-ionization structures (LISs) in the planetary nebula NGC 7009 from data obtained by the Multi Unit Spectroscopic Explorer (MUSE) integral field unit. This atomic carbon emission marks the transition zone between ionized and neutral gas and for the first time offers direct evidence that LISs are photodominated regions. The outer LIS pair exhibits intense lambda 8727 emission, but is absent. Conversely, the inner pair of knots shows both lines, likely due to the host nebula emission. Furthermore, the lambda 8727 line is absent in the host nebula emission, but lambda 8733 is present. Although the origin of the lambda 8727 line is still debated, its detection supports the scenario of photoevaporated dense molecular clumps.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"121 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141801820","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Non-radial oscillations mimicking a brown dwarf orbiting the cluster giant NGC 4349 No. 127","authors":"Dane Spaeth, S. Reffert, E. L. Hunt, A. Kaminski, A. Quirrenbach","doi":"10.1051/0004-6361/202450163","DOIUrl":"https://doi.org/10.1051/0004-6361/202450163","url":null,"abstract":"Several evolved stars have been found to exhibit long-period radial velocity variations that cannot be explained by planetary or brown dwarf companions. Non-radial oscillations caused by oscillatory convective modes have been put forth as an alternative explanation, but no modeling attempt has yet been undertaken. We provide a model of a non-radial oscillation, aiming to explain the observed variations of the cluster giant NGC 4349 No. 127. The star was previously reported to host a brown dwarf companion, but whose existence was later refuted in the literature. We reanalyzed 58 archival HARPS spectra of the intermediate-mass giant NGC 4349 No. 127. We reduced the spectra using the SERVAL and RACCOON pipelines, acquiring additional activity indicators. We searched for periodicity in the indicators and correlations between the indicators and radial velocities. We further present a simulation code able to produce synthetic HARPS spectra, incorporating the effect of non-radial oscillations, and compare the simulated results to the observed variations. We discuss the possibility that non-radial oscillations cause the observed variations. We find a positive correlation between chromatic index and radial velocity, along with closed-loop Lissajous-like correlations between radial velocity and each of the spectral line shape indicators (full width at half maximum, and contrast of the cross-correlation function and differential line width). Simulations of a low-amplitude, retrograde, dipole ($l=1, m=1$), non-radial oscillation can reproduce the observed behavior and explain the observables. Photometric variations below the detection threshold of the available ASAS-3 photometry are predicted. The oscillation and stellar parameters are largely in agreement with the prediction of oscillatory convective modes. The periodic variations of the radial velocities and activity indicators, along with the respective phase shifts, measured for the intermediate-mass cluster giant NGC 4349 No. 127, can be explained by a non-radial oscillation.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"28 11","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141799239","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"LyαNNA: A deep learning field-level inference machine for the Lyman-α forest","authors":"Parth Nayak, Michael Walther, Daniel Gruen, Sreyas Adiraju","doi":"10.1051/0004-6361/202348485","DOIUrl":"https://doi.org/10.1051/0004-6361/202348485","url":null,"abstract":"The inference of astrophysical and cosmological properties from the Lyman-alpha forest conventionally relies on summary statistics of the transmission field that carry useful but limited information. We present a deep learning framework for inference from the Lyman-alpha forest at the field level. This framework consists of a 1D residual convolutional neural network (ResNet) that extracts spectral features and performs regression on thermal parameters of the intergalactic medium that characterize the power-law temperature-density relation. We trained this supervised machinery using a large set of mock absorption spectra from Nyx hydrodynamic simulations at $z=2.2$ with a range of thermal parameter combinations (labels). We employed Bayesian optimization to find an optimal set of hyperparameters for our network, and then employed a committee of 20 neural networks for increased statistical robustness of the network inference. In addition to the parameter point predictions, our machine also provides a self-consistent estimate of their covariance matrix with which we constructed a pipeline for inferring the posterior distribution of the parameters. We compared the results of our framework with the traditional summary based approach, namely the power spectrum and the probability density function (PDF) of transmission, in terms of the area of the 68 credibility regions as our figure of merit (FoM). In our study of the information content of perfect (noise- and systematics-free) lya forest spectral datasets, we find a significant tightening of the posterior constraints --- factors of 10.92 and 3.30 in FoM over the power spectrum only and jointly with PDF, respectively --- which is the consequence of recovering the relevant parts of information that are not carried by the classical summary statistics.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"7 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141803021","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The MOPYS project: A survey of 70 planets in search of extended He i and H atmospheres. No evidence of enhanced evaporation in young planets","authors":"J. Orell-Miquel, F. Murgas, E. Pallé, M. Mallorquín, M. López-Puertas, M. Lampón, J. Sanz-Forcada, L. Nortmann, S. Czesla, E. Nagel, I. Ribas, M. Stangret, J. Livingston, E. Knudstrup, S. H. Albrecht, I. Carleo, J. A. Caballero, F. Dai, E. Esparza-Borges, A. Fukui, K. Heng, T. Henning, T. Kagetani, F. Lesjak, J.P. de Leon, D. Montes, G. Morello, N. Narita, A. Quirrenbach, P. Amado, A. Reiners, A. Schweitzer, J. I. Vico Linares","doi":"10.1051/0004-6361/202449411","DOIUrl":"https://doi.org/10.1051/0004-6361/202449411","url":null,"abstract":"During the first billion years of their life, exoplanet atmospheres are modified by different atmospheric escape phenomena that can strongly affect the shape and morphology of the exoplanet itself. These processes can be studied with Lyalpha , Halpha , and/or He i triplet observations.\u0000 We present high-resolution spectroscopy observations from CARMENES and GIARPS checking for He i and Halpha signals in 20 exoplanetary atmospheres: V1298,Tau,c, K2-100,b, HD,63433,b, HD,63433,c, HD,73583,b, HD,73583,c, K2-77,b, TOI-2076,b, TOI-2048,b, HD,235088,b, TOI-1807,b, TOI-1136,d, TOI-1268,b, TOI-1683,b, TOI-2018,b, MASCARA-2,b, WASP-189,b, TOI-2046,b, TOI-1431,b, and HAT-P-57,b. We report two new high-resolution spectroscopy He i detections for TOI-1268,b and TOI-2018,b, and a Halpha detection for TOI-1136,d. Furthermore, we detect hints of He i for HD,63433,b, and Halpha for HD,73583,b and c, which need to be confirmed. The aim of the Measuring Out-flows in Planets orbiting Young Stars (MOPYS) project is to understand the evaporating phenomena and test their predictions from the current observations. We compiled a list of 70 exoplanets with He i and/or Halpha observations, from this work and the literature, and we considered the He i and Halpha results as proxy for atmospheric escape.\u0000 Our principal results are that 0.1--1Gyr planets do not exhibit more He i or Halpha detections than older planets, and evaporation signals are more frequent for planets orbiting sim 1--3,Gyr stars. We provide new constraints to the cosmic shoreline, the empirical division between rocky planets and planets with atmosphere, by using the evaporation detections and we explore the capabilities of a new dimensionless parameter He /R_ Hill $, to explain the He i triplet detections. Furthermore, we present a statistically significant upper boundary for the He i triplet detections in the $T_ eq $ versus $ p $ parameter space. Planets located above that boundary are unlikely to show He i absorption signals.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"26 19","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141802823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sufficiency of near-surface water ice as a driver of dust activity on comets. Rethinking the old enigma","authors":"Y. Skorov, O. Mokhtari, W. Macher, V. Reshetnyk, J. Markkanen, Y. Zhao, N. Thomas, M. Kuppers, P. Hartogh","doi":"10.1051/0004-6361/202449433","DOIUrl":"https://doi.org/10.1051/0004-6361/202449433","url":null,"abstract":"Nearly all contemporary theoretical research on cometary dust activity relies on models depicting heat transfer and sublimation products within the near-surface porous layer. Gas flow exerts a pressure drag to the crust agglomerates, counteracting weak gravity and the tensile strength of that layer. Our interpretation of data from the Rosetta mission, and our broader comprehension of cometary activity, hinges significantly on the study of this process. We investigate the role played by the structure of the near-surface\u0000porous layer and its associated resistance to gas flow, tensile strength, pressure distribution, and other characteristics in the scenario of the potential release of dust agglomerates and the resulting dust activity. We employ a thermophysical model that factors in the microstructure of this layer and radiative heat conductivity. We consider gas flow in both the Knudsen and transition regimes. To accomplish this, we use methods such as test-particles Monte Carlo, direct-simulation Monte Carlo, and transmission probability. Our study encompasses a broad spectrum of dust-particle sizes. We evaluated the permeability of a dust layer composed of porous aggregates in the submillimetre and millimetre ranges. We carried out comparisons among various models that describe gas diffusion in a porous dust layer. For both the transition and Knudsen regimes, we obtained pressure profiles within a non-isothermal layer. We discuss how the gaps in our understanding of the structure and composition could impact tensile strength estimates. We demonstrate that for particles in the millimetre range, the lifting force of the sublimation products of water ice is adequate to remove the layer. This scenario remains feasible even for particles on the scale of hundreds of microns. This finding is crucial as the sublimation of water ice continues to be the most probable mechanism for dust removal. This study partially overturns the previously held, pessimistic view regarding the possibility of dust removal via water sublimation. We demonstrate that a more precise consideration of various physical processes allows elevation of the matter of dust activity to a practical plane, necessitating a fresh quantitative analysis.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"40 20","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141803772","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"KMT-2021-BLG-2609Lb and KMT-2022-BLG-0303Lb: Microlensing planets \u0000identified through signals produced by major-image perturbations","authors":"C. Han, M. Albrow, Chung-Uk Lee, S. Chung, A. Gould, K. Hwang, Y. Jung, Y. Ryu, Y. Shvartzvald, I. Shin, J. Yee, Hongjing Yang, W. Zang, S. Cha, Doeon Kim, Dong-Jin Kim, Seung-Lee Kim, Dong-Joo Lee, Yongseok Lee, B.-G. Park, R. Pogge","doi":"10.1051/0004-6361/202450873","DOIUrl":"https://doi.org/10.1051/0004-6361/202450873","url":null,"abstract":"We investigate microlensing data collected by the Korea Microlensing Telescope Network \u0000(KMTNet) survey during the 2021 and 2022 seasons to identify planetary lensing events \u0000displaying a consistent anomalous pattern. Our investigation reveals that the light curves \u0000of two lensing events, KMT-2021-BLG-2609 and KMT-2022-BLG-0303, exhibit a similar anomaly, \u0000in which short-term positive deviations appear on the sides of the low-magnification lensing \u0000light curves. To unravel the nature of these anomalies, we meticulously analyze each of the lensing events. \u0000Our investigations reveal that these anomalies stem from a shared channel, wherein the source \u0000passed near the planetary caustic induced by a planet with projected separations from the host \u0000star exceeding the Einstein radius. We find that interpreting the anomaly of KMT-2021-BLG-2609 \u0000is complicated by the \"inner--outer\" degeneracy, whereas for KMT-2022-BLG-0303, there is no such \u0000issue despite similar lens-system configurations. In addition to this degeneracy, interpreting \u0000the anomaly in KMT-2021-BLG-2609 involves an additional degeneracy between a pair of solutions, \u0000in which the source partially envelops the caustic and the other three solutions in which the \u0000source fully envelopes the caustic. As in an earlier case of this so-called von Schlieffen--Cannae \u0000degeneracy, the former solutions have substantially higher mass ratio. Through Bayesian analyses conducted based on the measured lensing observables of the event \u0000time scale and angular Einstein radius, the host of KMT-2021-BLG-2609L is determined to be \u0000a low-mass star with a mass $ 0.2 M_ in terms of a median posterior value, while the planet's mass ranges from approximately 0.032 to 0.112 times that of Jupiter, depending on the solutions. For the planetary system KMT-2022-BLG-0303L, it features a planet with a mass of approximately $0.51 J $ and a host star with a mass of about $0.37 M_ In both cases, the lenses are most likely situated in the bulge.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"25 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141808634","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The mass of the white dwarf in YY Dra (=DO Dra): Dynamical measurement and comparative study with X-ray estimates","authors":"Ayoze 'Alvarez-Hern'andez, Manuel A. P. Torres, Tariq Shahbaz, Pablo Rodr'iguez-Gil, K. Gazeas, Javier S'anchez-Sierras, P. Jonker, J. Corral-Santana, J. Acosta-Pulido, P. Hakala","doi":"10.1051/0004-6361/202451094","DOIUrl":"https://doi.org/10.1051/0004-6361/202451094","url":null,"abstract":"We present a dynamical study of the intermediate polar cataclysmic variable based on time-series observations in the $K$ band, where the donor star is known to be the major flux contributor. We covered the $3.97$-h orbital cycle with 44 spectra taken between $2020$ and $2022$ and two epochs of photometry observed in 2021 March and May. One of the light curves was simultaneously obtained with spectroscopy to better account for the effects of irradiation of the donor star and the presence of accretion light. From the spectroscopy, we derived the radial velocity curve of the donor star metallic absorption lines, constrained its spectral type to M0.5--M3.5 with no measurable changes in the effective temperature between the irradiated and non-irradiated hemispheres of the star, and measured its projected rotational velocity $v_ rot i = 103 km s $. Through simultaneous modelling of the radial velocity and light curves, we derived values for the radial velocity semi-amplitude of the donor star, $K_2 = 188^ the donor to white dwarf mass ratio, $q=M_2/M_1 = 0.62 0.02$, and the orbital inclination circ circ circ $. These binary parameters yield dynamical masses of $M_ M odot $ and $M_2 = 0.62^ M odot $ ($68$ per cent confidence level). As found for the intermediate polars GK Per and XY Ari, the white dwarf dynamical mass in YY Dra significantly differs from several\u0000estimates obtained by modelling the X-ray spectral continuum.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"22 12","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141810304","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A new atmospheric characterization of the sub-stellar companion HR 2562 B with JWST/MIRI observations","authors":"N. Godoy, E. Choquet, E. Serabyn, C. Danielski, T. Stolker, B. Charnay, S. Hinkley, P. Lagage, M. E. Ressler, P. Tremblin, A. Vigan","doi":"10.1051/0004-6361/202449951","DOIUrl":"https://doi.org/10.1051/0004-6361/202449951","url":null,"abstract":"HR,2562,B is a planetary-mass companion at an angular separation of $0.56 ($19$,au) from the host star, which is also a member of a select number of L/T transitional objects orbiting a young star. This companion gives us a great opportunity to contextualize and understand the evolution of young objects in the L/T transition. However, the main physical properties (e.g., $ T_ eff $ and mass) of this companion have not been well constrained (34 uncertainties on $ T_ eff $, 22 uncertainty for log(g)) using only near-infrared (NIR) observations. We aim to narrow down some of its physical parameters uncertainties (e.g., $ T_ eff $: 1200K-1700K, log(g): 4-5) incorporating new observations in the Rayleigh-Jeans tail with the JWST/MIRI filters at $10.65$, $11.40$, and $15.50 m$, as well as to understand its context in terms of the L/T transition and chemical composition. We processed the MIRI observations with reference star differential imaging (RDI) and detect the companion at high S/N (around $16$) in the three filters, allowing us to measure its flux and astrometry. We used two atmospheric models ATMO and Exo-REM to fit the spectral energy distribution using different combinations of mid-IR and near-IR datasets. We also studied the color-magnitude diagram using the F1065C and F1140C filters combined with field brown dwarfs to investigate the chemical composition in the atmosphere of HR,2562,B, as well as a qualitative comparison with the younger L/T transitional companion VHS,1256,b. We improved the precision on the temperature of HR,2562,B ($ T_ eff $ = $1255$,K) by a factor of $6 compared to previous estimates ($ vs $ using ATMO . The precision of its luminosity was also narrowed down to $-4.69 dex. The surface gravity still presents a wider range of values (4.4 to 4.8 dex). While its mass was not narrowed down, we find the most probable values between $8 M_ Jup $ ($3$-sigma lower limit from our atmospheric modeling) and $18.5 M_ Jup $ (from the upper limit provided by astrometric studies). We report a sensitivity to objects of mass ranging between $2-5 M_ Jup $ at $100$,au, reaching the lower limit at F1550C . We also implemented a few improvements in the pipeline related to the background subtraction and stages 1 and 2. HR,2562,B has a mostly (or near) cloud-free atmosphere, with the ATMO model demonstrating a better fit to the observations. From the color-magnitude diagram, the most probable chemical species at MIR wavelengths are silicates (but with a weak absorption feature); however, follow-up spectroscopic observations are necessary to either confirm or reject this finding. The mass of HR,2562,B could be better constrained with new observations at $3-4 m$. Although HR,2562,B and VHS,1256,b have very similar physical properties, both are in different evolutionary states in the L/T transition, which makes HR,2562,B an excellent candidate to complement our knowledge of young objects in this transition. Considering the actual range of possible ma","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"46 8","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141807111","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Asymmetries in asymptotic giant branch stars and their winds. I. From 3D RHD models to synthetic observables","authors":"Joachim Wiegert, B. Freytag, S. Hofner","doi":"10.1051/0004-6361/202450077","DOIUrl":"https://doi.org/10.1051/0004-6361/202450077","url":null,"abstract":"Asymptotic giant branch (AGB) stars are significant contributors to the metal enrichment of the interstellar medium. They have strong dust-driven winds that have their origin in regions close to the AGB star's surface, where dense dust clouds form. In this methods paper, we adapted models from advanced radiation-hydrodynamical (RHD) simulations as input for radiative transfer software to create synthetic observables. A major goal is to describe an AGB star's non-sphericity and to simulate its effects on the surrounding dusty envelope. We developed tools in Python to translate models of an AGB star and its dust-driven wind from 3D RHD simulations with into the format used for radiative transfer with . We preserved the asymmetric shape of the AGB star by including the star as a `dust species' and by using temperature data computed in The circumstellar silicate dust from the 3D RHD simulation is included using opacity data in with spatially dependent grain sizes. We compared images and spectral energy distributions (SEDs) created with of a model snapshot with similar output made with a spherically symmetric stellar atmosphere from the 1D program and with a point source star in Our model features substantial and clumpy dust formation just above 3.4,au from the grid centre ($ 1,R_ above the star), and large-scale structures due to giant convection cells are visible on the stellar surface. With the properties of VLTI as a basis, we have created simple synthetic observables where the dust clouds close to the star and features on the stellar surface are resolved. The flux density and the contrast to the star are high enough that optical interferometers, such as the VLTI, should be able to detect these dust clouds. We find that it is important to include asymmetric stellar models since their irregular shapes, radiation fields, and their dusty envelopes even put their marks on spatially unresolved observables and affect the flux levels and shapes of the SEDs. The effects on flux levels can mostly be linked to the clumpiness of the circumstellar dust. In contrast, the angle-dependent illumination resulting from temperature variations on the stellar surface causes shifts in the wavelengths of the flux maximum, as shown by replacing the asymmetric star with a spherical one. The methods presented here are an important step towards producing realistic synthetic observables and testing predictions of advanced 3D RHD models. With the model used here, we find that optical interferometers should be able to resolve thermal emission from dense clouds in the dust-formation zone close to an AGB star. Taking the angle-dependence of SEDs as a proxy for temporal variations in unresolved data, we conclude that not all variability observed in AGB stars should be interpreted as global changes in the sense of spherical models.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"78 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141807975","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Searching for the stellar cycles of low-mass stars using TESS data","authors":"Gavin Ramsay, Pasi Hakala, J. Gerry Doyle","doi":"10.1051/0004-6361/202450523","DOIUrl":"https://doi.org/10.1051/0004-6361/202450523","url":null,"abstract":"We carried out a search for stellar activity cycles in late\u0000 low-mass M dwarfs (M0--M6) located in the TESS northern and southern\u0000 continuous viewing zones using data from sectors 1--61 (Cycle 1 to\u0000 partway through Cycle 5). We utilised TESS-SPOC data, which\u0000 initially had a cadence of 30 min and was then reduced to 10 min in\u0000 Cycle 3. In addition, we required for each star to be observed in at\u0000 least six sectors in each north and south Cycle: 1,950 low-mass\u0000 stars ultimately met these criteria. Strong evidence was seen in 245\u0000 stars for a very stable photometric variation that we assumed to be\u0000 a signature of the stars' rotation period. We conducted a similar\u0000 study for solar-like stars and found that 194 out of 1432 stars had\u0000 a very stable modulation. We then searched for evidence of a\u0000 variation in the rotational amplitude. We found 26 low-mass stars\u0000 that showed evidence of variability in their photometric amplitude\u0000 and only one solar-like star. Some display a monotonic trend over\u0000 3--4 years, whilst others reveal shorter term variations. We\u0000 determined the predicted cycle durations of these stars using a\u0000 relationship found in the literature and an estimate of the\u0000 stars' Rossby number. Finally, we found a marginally statistically\u0000 significant correlation between the range in the rotational\u0000 amplitude modulation and the rotation period.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"80 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141808057","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}