Astronomy & Astrophysics最新文献

{"title":"Contemporaneous high-angular-resolution imaging of the AGB star W Hya in vibrationally excited H2O lines and visible polarized light with ALMA and VLT/SPHERE-ZIMPOL","authors":"K. Ohnaka, K. T. Wong, G. Weigelt, K.-H. Hofmann","doi":"10.1051/0004-6361/202451977","DOIUrl":"https://doi.org/10.1051/0004-6361/202451977","url":null,"abstract":"<i>Aims.<i/> We present contemporaneous high-angular-resolution millimeter imaging and visible polarimetric imaging of the nearby asymptotic giant branch (AGB) star W Hya to better understand the dynamics and dust formation within a few stellar radii.<i>Methods.<i/> The star W Hya was observed in two vibrationally excited H<sub>2<sub/>O lines at 268 and 251 GHz with Atacama Large Millimeter/submillimeter Array (ALMA) at a spatial resolution of 16 × 20 mas and at 748 and 820 nm at a resolution of 26 × 27 mas with the Very Large Telescope (VLT)/Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE)-Zurich Imaging Polarimeter (ZIMPOL).<i>Results.<i/> ALMA’s high spatial resolution allowed us to image strong emission of the vibrationally excited H<sub>2<sub/>O line at 268 GHz (<i>v<i/><sub>2<sub/> = 2, <i>J<i/><sub><i>K<i/><sub><i>a<i/><sub/>, <i>K<i/><sub><i>c<i/><sub/><sub/> = 6<sub>5, 2<sub/>–7<sub>4, 3<sub/>) over the stellar surface instead of absorption against the continuum, which is expected for thermal excitation. Strong, spotty emission was also detected along and just outside the stellar disk limb at an angular distance of ∼40 mas (∼1.9 <i>R<i/><sub>⋆<sub/>), extending to ∼60 mas (∼2.9 <i>R<i/><sub>⋆<sub/>). Another H<sub>2<sub/>O line (<i>v<i/><sub>2<sub/> = 2, <i>J<i/><sub><i>K<i/><sub><i>a<i/><sub/>, <i>K<i/><sub><i>c<i/><sub/><sub/> = 9<sub>2, 8<sub/>–8<sub>3, 5<sub/>) at 251 GHz with a similar upper-level energy was tentatively identified, which shows absorption over the stellar surface. This suggests that the emission over the surface seen in the 268 GHz H<sub>2<sub/>O line is suprathermal or even maser emission. The estimated gas temperature and H<sub>2<sub/>O density are consistent with the radiatively pumped masers. The 268 GHz H<sub>2<sub/>O line reveals global infall at up to ∼15 km s<sup>−1<sup/> within 2–3 <i>R<i/><sub>⋆<sub/>, but outflows at up to ∼8 km s<sup>−1<sup/> are also present. The polarized intensity maps obtained in the visible reveal clumpy dust clouds forming within ∼40 mas (∼1.9 <i>R<i/><sub>⋆<sub/>) with a particularly prominent cloud in the SW quadrant and a weaker cloud in the east. The 268 GHz H<sub>2<sub/>O emission overlaps very well with the visible polarized intensity maps, which suggests that both the nonthermal and likely maser H<sub>2<sub/>O emission and the dust originate from dense, cool pockets in the inhomogeneous atmosphere within ∼2–3 <i>R<i/><sub>⋆<sub/>.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"128 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142610564","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Performance comparison of the Shack-Hartmann and pyramid wavefront sensors with a laser guide star for 40 m telescopes","authors":"F. Oyarzún, C. Heritier, V. Chambouleyron, T. Fusco, P. Rouquette, B. Neichel","doi":"10.1051/0004-6361/202451670","DOIUrl":"https://doi.org/10.1051/0004-6361/202451670","url":null,"abstract":"<i>Context<i/>. Upcoming giant segmented mirror telescopes will use laser guide stars (LGS) for their adaptive optics (AO) systems. Two options of wavefront sensors (WFSs) are the Shack-Hartmann wavefront sensor (SHWFS) and the pyramid wavefront sensor (PWFS).<i>Aims<i/>. In this paper, we compare the noise performance of the PWFS and the SHWFS. We aim to identify which of the two is best to use in the context of a single or tomographic configuration.<i>Methods<i/>. To compute the noise performance, we extended a noise model developed for the PWFS to be used with the SHWFS. To do this, we expressed the centroiding algorithm of the SHWFS as a matrix-vector multiplication, which allowed us to use the statistics of noise to compute its propagation through the AO loop. We validated the noise model with end-to-end simulations for telescopes of 8 and 16 m in diameter.<i>Results<i/>. For an AO system with only one WFS, we found that given the same number of subapertures, the PWFS outperforms the SHWFS. For a 40 m telescope, the limiting magnitude of the PWFS is around one magnitude higher than the SHWFS. When using multiple WFS and a generalized least-squares estimator to combine the signal, our model predicts that in a tomographic system, the SHWFS performs better than the PWFS (with a limiting magnitude that is higher by a 0.3 magnitude. When using sub-electron RON detectors for the PWFS, the performance quality is almost identical for the two WFSs.<i>Conclusions<i/>. We find that when using a single WFS with LGS, PWFS is a better alternative than the SH. For a tomographic system, both sensors would give roughly the same performance.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"12 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142610471","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimised use of interferometry, spectroscopy, and stellar atmosphere models for determining the fundamental parameters of stars","authors":"N. Ebrahimkutty, M. R. Gent, D. Mourard, A. Domiciano de Souza, M. Bergemann, T. Morel, G. Morello, N. Nardetto, B. Plez","doi":"10.1051/0004-6361/202450105","DOIUrl":"https://doi.org/10.1051/0004-6361/202450105","url":null,"abstract":"<i>Context<i/>. Thanks to recent progress in the field of optical interferometry, instrument sensitivities have now reached the level achieved in the domain of new space missions dedicated to exoplanet and stellar studies. Combining interferometry with other observational approaches enables the determination of stellar parameters and helps improve our understanding of stellar physics.<i>Aims<i/>. In this paper, we aim to demonstrate a new way of using stellar atmosphere models for a joint interpretation of spectroscopic and interferometric observations.<i>Methods<i/>. Starting from a discrete grid of one-dimensional (1D) stellar atmosphere models, we developed a training algorithm, based on an artificial neural network, capable of estimating the spectrum and intensity profile of a star over a range of wavelengths and viewing angles. A minimisation algorithm based on the trained function allowed for the simultaneous fitting of the observational spectrum and interferometric complex visibilities. As a result, coherent and precise stellar parameters can be extracted.<i>Results<i/>. We show the ability of the trained function to match the modelled intensity profiles of stars in the effective temperature range of 4500–7000 K and surface gravity range of 3 to 5 dex, with a relative precision to the model that is better than 0.05%. Using simulated interferometric data and actual spectroscopic measurements, we demonstrated the performance of our algorithm on a sample of five benchmark stars. Using this method, we achieved an accuracy within 0.5% for the angular diameter, radius, and surface gravity, and within 20 K for the effective temperature.<i>Conclusions<i/>. This paper demonstrates a new method of using interferometric data combined with spectroscopic observations. This approach offers an improved determination of the radius, effective temperature, and surface gravity of stars.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"163 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142610552","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Tale of NGC 3785: The formation of an ultra-diffuse galaxy at the end of the longest tidal tail","authors":"Chandan Watts, Sudhanshu Barway, Omkar Bait, Yogesh Wadadekar","doi":"10.1051/0004-6361/202452002","DOIUrl":"https://doi.org/10.1051/0004-6361/202452002","url":null,"abstract":"<i>Aims.<i/> We present the discovery of an extended and faint tail observed in the isolated environment associated with galaxy NGC 3785. This study additionally provides observational evidence supporting the formation of ultra-diffuse galaxies (UDGs) at the end of the tail.<i>Methods.<i/> We utilized the Gnuastro software to detect and analyze the low surface brightness structures in the optical <i>g<i/>- and <i>r<i/>-bands using data from the Dark Energy Camera Legacy Survey. We created a detection map to identify the faint tail and measured its length using cubic spline fitting. Additionally, we found 84 star-forming clumps along the tail and performed photometric analysis on the tail portion after applying a significance threshold on the signal-to-noise ratio.<i>Results.<i/> We have measured the projected length of the tail, which is ∼390 kpc. We propose that this tail arises from the interaction of the NGC 3785 with a gas-rich galaxy, which ends up as a UDG at the end of the tail.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"44 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142610477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Venusian ion escape under extreme conditions: A dynamic pressure and temperature simulation study","authors":"M. C. Katrougkalou, M. Persson, S. Aizawa, N. André, R. Modolo, E. Jariel, A. Kullen, T. Karlsson","doi":"10.1051/0004-6361/202449326","DOIUrl":"https://doi.org/10.1051/0004-6361/202449326","url":null,"abstract":"<i>Context<i/>. We investigated the response of the Venusian atmospheric ion escape under the effect of interplanetary coronal mass ejections (ICMEs) using the Latmos Hybrid Simulation (LatHyS).<i>Aims<i/>. In particular, we focused on the influence of extreme ICME dynamic pressures and temperatures, with the temperature being a parameter that has not been extensively studied in the past.<i>Methods<i/>. Simulations were performed for two different dynamic pressures and three different temperatures. For the case of the dynamic pressure simulations, a density and a velocity enhancement event were studied separately. The H<sup>+<sup/> and O<sup>+<sup/> ion escape was then examined and compared for different escape channels.<i>Results<i/>. In both dynamic pressure enhancement cases, we find that there is no clear dependence of the O<sup>+<sup/> ion escape on the dynamic pressure, which is consistent with observations. On the other hand, the temperature of the incoming solar wind positively influences the H<sup>+<sup/> and O<sup>+<sup/> ion escape. This is attributed in part to the enhanced gyroradius of the particles, which allows them to penetrate deeper into the planet’s atmosphere.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"25 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142610362","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nebular dust attenuation with the Balmer and Paschen lines based on the MaNGA survey","authors":"Zesen Lin, Renbin Yan","doi":"10.1051/0004-6361/202451339","DOIUrl":"https://doi.org/10.1051/0004-6361/202451339","url":null,"abstract":"Dust attenuations observed by stars and ionized gas are not necessarily the same. The lack of observational constraints on the nebular dust attenuation curve leaves a large uncertainty when correcting nebular dust attenuation with stellar continuum-based attenuation curves. Making use of the DAP catalogs of the MaNGA survey, we investigate the nebular dust attenuation of H II regions traced by the Balmer and Paschen lines. Based on a simple simulation, we find that star-forming regions on kpc scales favor the classic foreground screen dust model rather than the uniform mixture model. We propose a novel approach to fit the dust attenuation curve using the emission-line fluxes directly. For strong hydrogen recombination lines (e.g., H<i>γ<i/>, H<i>δ<i/>, and H<i>ϵ<i/>), the slopes of the nebular attenuation curve can be well determined and are found to be in good agreement with the Fitzpatrick Milky Way extinction curve with an accuracy of ≲4% in terms of the correction factor. However, severe contaminations and/or systematic uncertainties prevent us from obtaining reasonable values of the slopes for weak recombination lines (e.g., the high-order Balmer lines or the Paschen lines). We discuss how the choice of emission line measurement methods affects the results. Our results demonstrate the difficulty of deriving an average nebular dust attenuation curve given the current ground-based emission-line measurements.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"13 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142610352","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Quantifying the informativity of emission lines to infer physical conditions in giant molecular clouds","authors":"Lucas Einig, Pierre Palud, Antoine Roueff, Jérôme Pety, Emeric Bron, Franck Le Petit, Maryvonne Gerin, Jocelyn Chanussot, Pierre Chainais, Pierre-Antoine Thouvenin, David Languignon, Ivana Bešlić, Simon Coudé, Helena Mazurek, Jan H. Orkisz, Miriam G. Santa-Maria, Léontine Ségal, Antoine Zakardjian, Sébastien Bardeau, Karine Demyk, Victor de Souza Magalhães, Javier R. Goicoechea, Pierre Gratier, Viviana V. Guzmán, Annie Hughes, François Levrier, Jacques Le Bourlot, Dariusz C. Lis, Harvey S. Liszt, Nicolas Peretto, Evelyne Roueff, Albrecht Sievers","doi":"10.1051/0004-6361/202451588","DOIUrl":"https://doi.org/10.1051/0004-6361/202451588","url":null,"abstract":"Observations of ionic, atomic, or molecular lines are performed to improve our understanding of the interstellar medium (ISM). However, the potential of a line to constrain the physical conditions of the ISM is difficult to assess quantitatively, because of the complexity of the ISM physics. The situation is even more complex when trying to assess which combinations of lines are the most useful. Therefore, observation campaigns usually try to observe as many lines as possible for as much time as possible. We have searched for a quantitative statistical criterion to evaluate the full constraining power of a (combination of) tracer(s) with respect to physical conditions. Our goal with such a criterion is twofold. First, we want to improve our understanding of the statistical relationships between ISM tracers and physical conditions. Secondly, by exploiting this criterion, we aim to propose a method that helps observers to make their observation proposals; for example, by choosing to observe the lines with the highest constraining power given limited resources and time. We propose an approach based on information theory, in particular the concepts of conditional differential entropy and mutual information. The best (combination of) tracer(s) is obtained by comparing the mutual information between a physical parameter and different sets of lines. The presented analysis is independent of the choice of the estimation algorithm ( neural network or $ minimization). We applied this method to simulations of radio molecular lines emitted by a photodissociation region similar to the Horsehead Nebula. In this simulated data, we considered the noise properties of a state-of-the-art single dish telescope such as the IRAM 30m telescope. We searched for the best lines to constrain the visual extinction or the ultraviolet illumination field . We ran this search for different gas regimes, namely translucent gas, filamentary gas, and dense cores. The most informative lines change with the physical regime ( cloud extinction). However, the determination of the optimal (combination of) line(s) to constrain a physical parameter such as the visual extinction depends not only on the radiative transfer of the lines and chemistry of the associated species, but also on the achieved mean signal-to-noise ratio. The short integration time of the CO isotopologue $J=1-0$ lines already yields much information on the total column density for a large range of ( ) space. The best set of lines to constrain the visual extinction does not necessarily combine the most informative individual lines. Precise constraints on the radiation field are more difficult to achieve with molecular lines. They require spectral lines emitted at the cloud surface ( and lines). This approach allows one to better explore the knowledge provided by ISM codes, and to guide future observation campaigns.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"71 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598499","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evolution of gas envelopes and outgassed atmospheres of rocky planets that formed via pebble accretion","authors":"Piia Maria Tomberg, Anders Johansen","doi":"10.1051/0004-6361/202451114","DOIUrl":"https://doi.org/10.1051/0004-6361/202451114","url":null,"abstract":"In this work, we present results of numerical simulations of the formation and early evolution of rocky planets through pebble accretion, with an emphasis on hydrogen envelope longevity and the composition of the outgassed atmosphere. We modelled planets with a range in mass from 0.1 to 5 Earth masses that orbit between 0.7 and 1.7 AU. The composition of the outgassed atmosphere was calculated with the partial pressure of free oxygen fit to geophysical models of magma ocean self-oxidation. The combined X-ray and UV (XUV) radiation-powered photoevaporation is considered as the main driver of atmospheric escape. We modelled planets that remain below the pebble isolation mass and hence accrete tenuous envelopes only. We considered slow, medium, or fast initial stellar rotation for the temporal evolution of the XUV flux. The loss of the envelope is a key event that allows the magma ocean to crystallise and outgas its bulk volatiles. The atmospheric composition of the majority of our simulated planets is dominated by CO$_2$. Our planets accrete a total of 11.6 Earth oceans of water, the majority of which enters the core. The hydrospheres of planets lighter than the Earth reach several times the mass of the Earth's modern oceans, while the hydrospheres of planets ranging from 1 to 3.5 Earth masses are comparable to those of our planet. However, planets of 4-5 Earth masses have smaller hydrospheres due to the trapping of volatiles in their massive mantles. Overall, our simulations demonstrate that hydrogen envelopes are easily lost from rocky planets and that this envelope loss triggers the most primordial partitioning of volatiles between the solid mantle and the atmosphere.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"10 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598503","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"ELEPHANT: ExtragaLactic alErt Pipeline for Hostless AstroNomical Transients","authors":"P.J. Pessi, R. Durgesh, L. Nakazono, E. Hayes, R.A.P. Oliveira, E.O. Ishida, A. Moitinho, A. Krone-Martins, B. Moews, R.S. de Souza, R. Beck, M.A. Kuhn, K. Nowak, S. Vaughan","doi":"10.1051/0004-6361/202450535","DOIUrl":"https://doi.org/10.1051/0004-6361/202450535","url":null,"abstract":"Transient astronomical events that exhibit no discernible association with a host galaxy are commonly referred to as hostless. These rare phenomena can offer unique insights into the properties and evolution of stars and galaxies. However, the sheer number of transients captured by contemporary high-cadence astronomical surveys renders the manual identification of all potential hostless transients impractical. Therefore, creating a systematic identification tool is crucial for studying these elusive events. We present the ExtragaLactic alErt Pipeline for Hostless AstroNomical Transients ( a framework for filtering hostless transients in astronomical data streams. It was designed to process alerts from the Zwicky Transient Facility (ZTF) presented in the Fink broker; however, its underlying concept can be applied to other data sources. We used Fink to access all the ZTF alerts produced between January 2022 and December 2023, selecting alerts associated with extragalactic transients reported in SIMBAD or TNS, as well as those classified as supernovae (SNe) or kilonovae (KNe) by the machine learning (ML) classifiers within the broker. We then processed the associated stamps using a sequence of image analysis techniques to retrieve hostless candidates. We find that lesssim 2<!PCT!> of all analyzed transients are potentially hostless. Among them, only sim 10<!PCT!> have a spectroscopic class reported on TNS, with type Ia SNe being the most common class, followed by superluminous SNe. In particular, among the hostless candidates retrieved by our pipeline, there is SN 2018ibb, which has been proposed to be a pair instability SN candidate, and SN 2022ann, one of only five known SNe Icn. When no class is reported on TNS, the dominant classes are quasi-stellar object (QSO) and SN candidates, with the former obtained from SIMBAD and the latter inferred using the Fink ML classifier. represents an effective strategy to filter extragalactic events within large and complex astronomical alert streams. There are many applications for which this pipeline will be useful, ranging from transient selection for follow-up to studies of transient environments. The results presented here demonstrate the feasibility of developing specially crafted pipelines that enable a variety of scientific studies based on large-scale surveys.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"196 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598505","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dependence of the polytropic behaviour of solar wind protons on temperature anisotropy and plasma β near L1","authors":"C. Katsavrias, G. Nicolaou, G. Livadiotis","doi":"10.1051/0004-6361/202452168","DOIUrl":"https://doi.org/10.1051/0004-6361/202452168","url":null,"abstract":"<i>Context.<i/> A polytropic process describes the transition of a fluid from one state to another through a specific relationship between the fluid density and temperature, while the value of the polytropic index that governs this relationship determines the heat transfer and the effective degrees of freedom of that specific process.<i>Aims.<i/> In this paper we investigate in depth the relationship between the proton effective polytropic index <i>γ<i/> in the solar wind, the proton anisotropy <i>α<i/>, and plasma <i>β<i/>, while – for the first time to our knowledge to such an extent – we further investigate the dependence of the partial (with respect to the magnetic field) polytropic index to both the above-mentioned plasma parameters.<i>Methods.<i/> To this end we use the entire Wind dataset spanning the 1995 to 2023 time period to derive the distributions of the polytropic index in the near-Earth space (L1).<i>Results.<i/> Our results indicate that the proton <i>γ<i/> increases with increasing proton anisotropy and decreases with increasing plasma <i>β<i/>. Finally, we show that even though the average (over long time periods) total and partial proton polytropic index values are very close, these values correspond to isotropic plasma alone, with a further balance between the thermal and magnetic pressure.On the contrary, for shorter time periods and/or specific solar wind structures, where the proton anisotropy and plasma <i>β<i/> exhibit deviations from these average values, the partial proton polytropic index exhibits significant variation that is dependent on the anisotropy and on plasma <i>β<i/>.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"95 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598500","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}