Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202450288
T.H. Pramono, M. Kenworthy, R. van Boekel
The early-type star ASASSN-21js started to fade in 2021, as was detected by the All Sky Automated Survey for Supernovae, undergoing a multi-year eclipse that is still underway. We interpret this event as being due to a structured disc of material transiting in front of the star. The disc is in orbit around a substellar object with the mass and luminosity of a brown dwarf or smaller. We want to determine the expected duration and ending date of the eclipse. We modelled a tilted and inclined azimuthally symmetric ring system around an unseen companion and calculated the resulting time-varying light curve as the object transited in front of the star. We made an initial estimate of the ring parameters and used these as inputs to an MCMC algorithm to determine the geometric properties of the rings with associated uncertainties. The model most consistent with the light curve to date is a two-ring system at high inclination with respect to the line of sight that has a semi-major axis of 71.6 stellar radii. With an estimate of the stellar radius, the transverse velocity is around 0.7 which if bound to the star is an orbit with a semi-major axis of around 13000 au, placing it in the Oort cloud of the parent star. The transit is ongoing and will finish around MJD 61526 (May 1 2027). We encourage the community to continue observing this object in order to understand its properties.
{"title":"ASASSN-21js: A multi-year transit of a ringed disc","authors":"T.H. Pramono, M. Kenworthy, R. van Boekel","doi":"10.1051/0004-6361/202450288","DOIUrl":"https://doi.org/10.1051/0004-6361/202450288","url":null,"abstract":"The early-type star ASASSN-21js started to fade in 2021, as was detected by the All Sky Automated Survey for Supernovae, undergoing a multi-year eclipse that is still underway.\u0000 \u0000 We interpret this event as being due to a structured disc of material transiting in front of the star.\u0000 \u0000 The disc is in orbit around a substellar object with the mass and luminosity of a brown dwarf or smaller.\u0000 \u0000 We want to determine the expected duration and ending date of the eclipse. We modelled a tilted and inclined azimuthally symmetric ring system around an unseen companion and calculated the resulting time-varying light curve as the object transited in front of the star.\u0000 \u0000 We made an initial estimate of the ring parameters and used these as inputs to an MCMC algorithm to determine the geometric properties of the rings with associated uncertainties. The model most consistent with the light curve to date is a two-ring system at high inclination with respect to the line of sight that has a semi-major axis of 71.6 stellar radii.\u0000 \u0000 With an estimate of the stellar radius, the transverse velocity is around 0.7 which if bound to the star is an orbit with a semi-major axis of around 13000 au, placing it in the Oort cloud of the parent star.\u0000 \u0000 The transit is ongoing and will finish around MJD 61526 (May 1 2027).\u0000 \u0000 We encourage the community to continue observing this object in order to understand its properties.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"15 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141808016","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}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202451215
S. Bagnulo, J. Landstreet, J. Farihi, C. Folsom, M. Hollands, L. Fossati
More than 30 of white dwarfs exhibit atmospheric metals, which are understood to be from recent or ongoing accretion of circumstellar debris. In cool white dwarfs, surface motions should rapidly homogenise photospheric abundances, and the accreted heavy elements should diffuse inward on a timescale much longer than that for surface mixing. The recent discovery of a metal scar on WD,0816--310 implies its $B 140$,kG magnetic field has impeded surface mixing of metals near the visible magnetic pole. Here, we report the discovery of a second magnetic, metal-polluted white dwarf, WD,2138--332, which exhibits periodic variability in longitudinal field, metal line strength, and broadband photometry. All three variable quantities have the same period, and show remarkable correlations: the published light curves have a brightness minimum exactly when the longitudinal field and line strength have a maximum, and a maximum when the longitudinal field and line strength have a minimum. The simplest interpretation of the line strength variability is that there is an enhanced metal concentration around one pole of the magnetic field; however, the variable line-blanketing cannot account for the observed multi-band light curves. More theoretical work is required to understand the efficiency of horizontal mixing of the accreted metal atoms, and the origin of photometric variability. Because both magnetic, metal-polluted white dwarfs that have been monitored to date show that metal line strengths vary in phase with the longitudinal field, we suggest that metal scars around magnetic poles may be a common feature of metal-polluted white dwarfs.
{"title":"Metal accretion scars may be common on magnetic, polluted white dwarfs","authors":"S. Bagnulo, J. Landstreet, J. Farihi, C. Folsom, M. Hollands, L. Fossati","doi":"10.1051/0004-6361/202451215","DOIUrl":"https://doi.org/10.1051/0004-6361/202451215","url":null,"abstract":"More than 30 of white dwarfs exhibit atmospheric metals, which are understood to be from recent or ongoing accretion of circumstellar debris. In cool white dwarfs, surface motions should rapidly homogenise photospheric abundances, and the accreted heavy elements should diffuse inward on a timescale much longer than that for surface mixing. The recent discovery of a metal scar on WD,0816--310 implies its $B 140$,kG magnetic field has impeded surface mixing of metals near the visible magnetic pole. Here, we report the discovery of a second magnetic, metal-polluted white dwarf, WD,2138--332, which exhibits periodic variability in longitudinal field, metal line strength, and broadband photometry. All three variable quantities have the same period, and show remarkable correlations: the published light curves have a brightness minimum exactly when the longitudinal field and line strength have a maximum, and a maximum when the longitudinal field and line strength have a minimum. The simplest interpretation of the line strength variability is that there is an enhanced metal concentration around one pole of the magnetic field; however, the variable line-blanketing cannot account for the observed multi-band light curves. More theoretical work is required to understand the efficiency of horizontal mixing of the accreted metal atoms, and the origin of photometric variability. Because both magnetic, metal-polluted white dwarfs that have been monitored to date show that metal line strengths vary in phase with the longitudinal field, we suggest that metal scars around magnetic poles may be a common feature of metal-polluted white dwarfs.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"56 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141808497","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}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202348352
P.J. Wang, Y.P. Chen, L. Ji, S. Zhang, S. Zhang, L.D. Kong, Z. Chang, L. Zhang, L. Tao, J. L. Qu, M. Ge, J. Li, J. Peng, Q. Shui, Z.S. Li
We report the results of our analysis of 83 type-I bursts during the 2022 outburst of the newly discovered accreting millisecond pulsar MAXI J1816--195 based on Insight-HXMT and NICER observations. We focus on the burst-recurrence time and its correlation with persistent flux and outburst evolution. The extensive observations of Insight-HXMT and NICER confirm the presence of quasi-periodic thermonuclear bursts during this outburst, with a recurrence time in the range of 1.15 to 2 hours, which varies with the source persistent flux. The burst recurrence times are, in general, longer at comparable flux levels in the outburst rising phase than those in the fading phase, forming an apparent hysteresis phenomenon. These burst properties make MAXI J1816--195 a unique target for investigating the underlying burst-accretion mechanisms. We discuss the plausible explanations for the hysteresis phenomenon, which appears to be related to changes in the ignition condition or accretion geometry during the outburst.
{"title":"Burst-recurrence properties revealed with Insight-HXMT and NICER for the newly discovered accreting millisecond pulsar MAXI J1816--195","authors":"P.J. Wang, Y.P. Chen, L. Ji, S. Zhang, S. Zhang, L.D. Kong, Z. Chang, L. Zhang, L. Tao, J. L. Qu, M. Ge, J. Li, J. Peng, Q. Shui, Z.S. Li","doi":"10.1051/0004-6361/202348352","DOIUrl":"https://doi.org/10.1051/0004-6361/202348352","url":null,"abstract":"We report the results of our analysis of 83 type-I bursts during the 2022 outburst of the newly discovered accreting millisecond pulsar MAXI J1816--195 based on Insight-HXMT and NICER observations. We focus on the burst-recurrence time and its correlation with persistent flux and outburst evolution. The extensive observations of Insight-HXMT and NICER confirm the presence of quasi-periodic thermonuclear bursts during this outburst, with a recurrence time in the range of 1.15 to 2 hours, which varies with the source persistent flux.\u0000 The burst recurrence times are, in general, longer at comparable flux levels in the outburst rising phase than those in the fading phase, forming an apparent hysteresis phenomenon.\u0000 These burst properties make MAXI J1816--195 a unique target for investigating the underlying burst-accretion mechanisms.\u0000 We discuss the plausible explanations for the hysteresis phenomenon, which appears to be related to changes in the ignition condition or\u0000 accretion geometry during the outburst.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"40 16","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141809806","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}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202450038
J. Lipták, M. Skarka, E. Guenther, P. Chaturvedi, M. V'itkov'a, R. Karjalainen, J. Šubjak, A. Hatzes, A. Bieryla, D. Gandolfi, S. H. Albrecht, P. G. Beck, H. Deeg, M. Everett, J. Higuera, D. Jones, S. Mathur, Y. G. Patel, C. Persson, S. Redfield, P. Kabáth
Precise space-based photometry from the Transiting Exoplanet Survey Satellite results in a huge number of exoplanetary candidates. However, the masses of these objects are unknown and must be determined by ground-based spectroscopic follow-up observations, frequently revealing the companions to be low-mass stars rather than exoplanets. We present the first orbital and stellar parameter solutions for five such eclipsing binary-star systems using radial-velocity follow-up measurements together with spectral-energy-distribution solutions. TOI-416 and TOI-1143 are totally eclipsing F+M star systems with well-determined secondary masses, radii, and temperatures. TOI-416 is a circular system with an F6 primary and a secondary with a mass of $M_2= M_ odot $. TOI-1143 consists of an F6 primary with an $M_2= M_ odot $ secondary on an eccentric orbit with a third companion. With respect to the other systems, TOI-1153 shows ellipsoidal variations, TOI-1615 contains a pulsating primary, and TOI-1788 has a spotted primary, while all have moderate mass ratios of 0.2-0.4. However, these systems are in a grazing configuration, which limits their full description. The parameters of TOI-416B and TOI-1143B are suitable for the calibration of the radius-mass relation for dwarf stars.
{"title":"Five new eclipsing binaries with low-mass companions","authors":"J. Lipták, M. Skarka, E. Guenther, P. Chaturvedi, M. V'itkov'a, R. Karjalainen, J. Šubjak, A. Hatzes, A. Bieryla, D. Gandolfi, S. H. Albrecht, P. G. Beck, H. Deeg, M. Everett, J. Higuera, D. Jones, S. Mathur, Y. G. Patel, C. Persson, S. Redfield, P. Kabáth","doi":"10.1051/0004-6361/202450038","DOIUrl":"https://doi.org/10.1051/0004-6361/202450038","url":null,"abstract":"Precise space-based photometry from the Transiting Exoplanet Survey Satellite results in a huge number of exoplanetary candidates. However, the masses of these objects are unknown and must be determined by ground-based spectroscopic follow-up observations, frequently revealing the companions to be low-mass stars rather than exoplanets. We present the first orbital and stellar parameter solutions for five such eclipsing binary-star systems using radial-velocity follow-up measurements together with spectral-energy-distribution solutions. TOI-416 and TOI-1143 are totally eclipsing F+M star systems with well-determined secondary masses, radii, and temperatures. TOI-416 is a circular system with an F6 primary and a secondary with a mass of $M_2= M_ odot $. TOI-1143 consists of an F6 primary with an $M_2= M_ odot $ secondary on an eccentric orbit with a third companion. With respect to the other systems, TOI-1153 shows ellipsoidal variations, TOI-1615 contains a pulsating primary, and TOI-1788 has a spotted primary, while all have moderate mass ratios of 0.2-0.4. However, these systems are in a grazing configuration, which limits their full description. The parameters of TOI-416B and TOI-1143B are suitable for the calibration of the radius-mass relation for dwarf stars.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"26 12","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141806156","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}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202449439
E. Arjona-Gálvez, Arianna Di Cintio, R. Grand
Recent observational studies suggest that feedback from active galactic nuclei (AGNs) may play an important role in the formation and evolution of dwarf galaxies, an issue that has received little attention from a theoretical perspective. We investigated this using two sets of 12 cosmological magnetohydrodynamic simulations of the formation of dwarf galaxies (10$^ M_ M$_ M_ one set using a version of the AURIGA galaxy formation physics model including AGN feedback and a parallel set with AGN feedback turned off. We show that the full-physics AGN runs satisfactorily reproduce several scaling relations, including the black-hole-to-stellar mass (M$_ BH $-M$_ star $), the black-hole-to-sigma (M$_ BH and the baryonic Tully-Fisher relation. We find that the global star formation (SF) of galaxies run with an AGN is reduced compared to the one in which the AGN has been turned off, suggesting that AGN feedback is a viable way of suppressing SF in dwarf galaxies, even though none of our galaxies is completely quenched by $z$=$0$. Furthermore, we find a tight correlation between the median SF rates and the BH $/M$_ star $ ratio in our simulated dwarfs. Star formation is suppressed due to gas heating in the vicinity of the AGN: less HI gas is available in AGN runs, though the total amount of gas is preserved across the two settings within each galaxy. This indicates that the main effect of AGN feedback in our dwarfs is to heat up and push the gas away from the galaxy's centre rather than expelling it completely. Finally, we show that the two galaxies harbouring the largest supermassive black holes have suffered a considerable (up to sim 65$,$) reduction in their central dark matter density, pinpointing the role of AGNs in determining the final dark matter mass distribution within dwarf galaxies. This pilot paper highlights the importance of modelling AGN feedback at the lowest mass scales and the impact this can have on dwarf galaxy evolution.
{"title":"The role of active galactic nucleus feedback on the evolution of dwarf galaxies from cosmological simulations. Supermassive black holes suppress star formation in low-mass galaxies","authors":"E. Arjona-Gálvez, Arianna Di Cintio, R. Grand","doi":"10.1051/0004-6361/202449439","DOIUrl":"https://doi.org/10.1051/0004-6361/202449439","url":null,"abstract":"Recent observational studies suggest that feedback from active galactic nuclei (AGNs) may play an important role in the formation and evolution of dwarf galaxies, an issue that has received little attention from a theoretical perspective. We investigated this using two sets of 12 cosmological magnetohydrodynamic simulations of the formation of dwarf galaxies (10$^ M_ M$_ M_ one set using a version of the AURIGA galaxy formation physics model including AGN feedback and a parallel set with AGN feedback turned off. We show that the full-physics AGN runs satisfactorily reproduce several scaling relations, including the black-hole-to-stellar mass (M$_ BH $-M$_ star $), the black-hole-to-sigma (M$_ BH and the baryonic Tully-Fisher relation. We find that the global star formation (SF) of galaxies run with an AGN is reduced compared to the one in which the AGN has been turned off, suggesting that AGN feedback is a viable way of suppressing SF in dwarf galaxies, even though none of our galaxies is completely quenched by $z$=$0$. Furthermore, we find a tight correlation between the median SF rates and the BH $/M$_ star $ ratio in our simulated dwarfs. Star formation is suppressed due to gas heating in the vicinity of the AGN: less HI gas is available in AGN runs, though the total amount of gas is preserved across the two settings within each galaxy. This indicates that the main effect of AGN feedback in our dwarfs is to heat up and push the gas away from the galaxy's centre rather than expelling it completely. Finally, we show that the two galaxies harbouring the largest supermassive black holes have suffered a considerable (up to sim 65$,$) reduction in their central dark matter density, pinpointing the role of AGNs in determining the final dark matter mass distribution within dwarf galaxies. This pilot paper highlights the importance of modelling AGN feedback at the lowest mass scales and the impact this can have on dwarf galaxy evolution.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"54 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141807516","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}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202450429
A. Ershova, J. Schmidt, F. Postberg, N. Khawaja, L. Nolle, R. Srama, S. Kempf, B. Southworth
We analyzed data recorded by the Cosmic Dust Analyzer on board the Cassini spacecraft during Enceladus dust plume traversals. Our focus was on profiles of relative abundances of grains of different compositional types derived from mass spectra recorded with the Dust Analyzer subsystem during the Cassini flybys E5 and E17. The E5 profile, corresponding to a steep and fast traversal of the plume, has already been analyzed. In this paper, we included a second profile from the E17 flyby involving a nearly horizontal traversal of the south polar terrain at a significantly lower velocity. Additionally, we incorporated dust detection rates from the High Rate Detector subsystem during flybys E7 and E21. We derived grain size ranges in the different observational data sets and used these data to constrain parameters for a new dust plume model. This model was constructed using a mathematical description of dust ejection implemented in the software package DUDI. Further constraints included published velocities of gas ejection, positions of gas and dust jets, and the mass production rate of the plume. Our model employs two different types of sources: diffuse sources of dust ejected with a lower velocity and jets with a faster and more colimated emission. From our model, we derived dust mass production rates for different compositional grain types, amounting to at least 28 kg/s. Previously, salt-rich dust was believed to dominate the plume mass based on E5 data alone. The E17 profile shows a dominance of organic-enriched grains over the south polar terrain, a region not well constrained by E5 data. By including both E5 and E17 profiles, we find the salt-rich dust contribution to be at most 1 by mass. This revision also results from an improved understanding of grain masses of various compositional types that implies smaller sizes for salt-rich grains. Our new model can predict grain numbers and masses for future mission detectors during plume traversals.
{"title":"Modeling the Enceladus dust plume based on in situ measurements performed with the Cassini Cosmic Dust Analyzer","authors":"A. Ershova, J. Schmidt, F. Postberg, N. Khawaja, L. Nolle, R. Srama, S. Kempf, B. Southworth","doi":"10.1051/0004-6361/202450429","DOIUrl":"https://doi.org/10.1051/0004-6361/202450429","url":null,"abstract":"We analyzed data recorded by the Cosmic Dust Analyzer on board the Cassini spacecraft during Enceladus dust plume traversals. Our focus was on profiles of relative abundances of grains of different compositional types derived from mass spectra recorded with the Dust Analyzer subsystem during the Cassini flybys E5 and E17. The E5 profile, corresponding to a steep and fast traversal of the plume, has already been analyzed. In this paper, we included a second profile from the E17 flyby involving a nearly horizontal traversal of the south polar terrain at a significantly lower velocity. Additionally, we incorporated dust detection rates from the High Rate Detector subsystem during flybys E7 and E21. We derived grain size ranges in the different observational data sets and used these data to constrain parameters for a new dust plume model. This model was constructed using a mathematical description of dust ejection implemented in the software package DUDI. Further constraints included published velocities of gas ejection, positions of gas and dust jets, and the mass production rate of the plume. Our model employs two different types of sources: diffuse sources of dust ejected with a lower velocity and jets with a faster and more colimated emission. From our model, we derived dust mass production rates for different compositional grain types, amounting to at least 28 kg/s. Previously, salt-rich dust was believed to dominate the plume mass based on E5 data alone. The E17 profile shows a dominance of organic-enriched grains over the south polar terrain, a region not well constrained by E5 data. By including both E5 and E17 profiles, we find the salt-rich dust contribution to be at most 1 by mass. This revision also results from an improved understanding of grain masses of various compositional types that implies smaller sizes for salt-rich grains. Our new model can predict grain numbers and masses for future mission detectors during plume traversals.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"56 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141808494","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}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202451146
S. V. von Fellenberg, G. Witzel, M. Bauboeck, Hui-Hsuan Chung, N. Marchili, Greg Martinez, Matteo Sadun-Bordoni, G. Bourdarot, Tuan Do, Antonia Drescher, Giovanni Fazio, F. Eisenhauer, R. Genzel, S. Gillessen, Joseph L. Hora, F. Mang, Thomas Ott, A. Howard Smith, Eduardo Ros, Diogo C. Ribeiro, F. Widmann, S. Willner, J. Anton Zensus
A systematic study, based on the third-moment structure function, of Sgr A*'s variability finds an exponential rise time, $ obs minutes $, and decay time, $ obs minutes $. This symmetry of the flux-density variability is consistent with earlier work, and we interpret it as being caused by the dominance of Doppler boosting, as opposed to gravitational lensing, in Sgr A*'s light curve. A relativistic, semi-physical model of Sgr A* confirms an inclination angle of $i The model also shows that the emission of the intrinsic radiative process can have some asymmetry even though the observed emission does not. The third-moment structure function, which is a measure of the skewness of the light-curve increments, may be a useful summary statistic in other contexts of astronomy because it senses only temporal asymmetry; that is, it averages to zero for any temporally symmetric signal.
{"title":"General relativistic effects and the near-infrared variability of Sgr A*. II. A systematic approach to temporal asymmetry","authors":"S. V. von Fellenberg, G. Witzel, M. Bauboeck, Hui-Hsuan Chung, N. Marchili, Greg Martinez, Matteo Sadun-Bordoni, G. Bourdarot, Tuan Do, Antonia Drescher, Giovanni Fazio, F. Eisenhauer, R. Genzel, S. Gillessen, Joseph L. Hora, F. Mang, Thomas Ott, A. Howard Smith, Eduardo Ros, Diogo C. Ribeiro, F. Widmann, S. Willner, J. Anton Zensus","doi":"10.1051/0004-6361/202451146","DOIUrl":"https://doi.org/10.1051/0004-6361/202451146","url":null,"abstract":"A systematic study, based on the third-moment structure function, of Sgr A*'s variability finds an exponential rise time, $ obs minutes $, and decay time, $ obs minutes $. This symmetry of the flux-density variability is consistent with earlier work, and we interpret it as being caused by the dominance of Doppler boosting, as opposed to gravitational lensing, in Sgr A*'s light curve. A relativistic, semi-physical model of Sgr A* confirms an inclination angle of $i The model also shows that the emission of the intrinsic radiative process can have some asymmetry even though the observed emission does not. The third-moment structure function, which is a measure of the skewness of the light-curve increments, may be a useful summary statistic in other contexts of astronomy because it senses only temporal asymmetry; that is, it averages to zero for any temporally symmetric signal.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"8 8","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141809258","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}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202450986
G. Alecian, M. Stift
Ambipolar diffusion of hydrogen gives an additional upward thrust to metals that diffuse in the atmosphere of Ap stars. Its quantitative effect on the build-up of abundance stratification due to atomic diffusion that produces the observed abundance anomalies in Ap stars has not been evaluated so far. The purpose of this work is to quantify this effect throughout the stratification process of metals inside the atmosphere. We used our code caratmotion to compute the time-dependent atomic diffusion of four metals (Mg, Ca, Si, and Fe) in the atmosphere of a main-sequence star with an effective temperature of $8,500$,K, which is a typical temperature of Ap stars. The results, including ambipolar diffusion of H, are compared to results obtained without this process. Our main result is that ambipolar diffusion must be included in any calculation of atomic diffusion in Ap star atmospheres, at least for stars with $T_ eff 10,000$,K. We show that this concerns all metals, even those that are well supported by the radiation field, such as Fe. The crucial role of the stellar mass-loss rate is confirmed; it remains a determining parameter that is constrained, but still free in our calculations. We also present 3D calculations of Ca distributions in magnetic atmospheres. Questioning the interest of systematic searches for stationary solutions (which can often only be reached after a long evolutionary process), we note that remarkable behaviour can occur during the transient phases of the stratification build-up.
氢的常极性扩散为在Ap星大气中扩散的金属提供了额外的向上推力。迄今为止，还没有评估过它对原子扩散导致的丰度分层的定量影响，而原子扩散会在Ap星中产生观测到的丰度异常。这项工作的目的是量化大气层内金属分层过程中的这种影响。我们使用 Caratmotion 代码计算了主序星大气中四种金属（Mg、Ca、Si 和 Fe）随时间变化的原子扩散，主序星的有效温度为 $8,500$,K，这是 Ap 星的典型温度。我们将包括H的伏极扩散在内的结果与没有这一过程的结果进行了比较。我们的主要结果是，在计算Ap恒星大气中的原子扩散时，必须包括伏极扩散，至少对于T_ eff为10,000美元（K）的恒星是这样。我们的研究表明，这涉及到所有金属，甚至包括那些辐射场支持良好的金属，比如铁。恒星质量损失率的关键作用得到了证实；它仍然是一个决定性参数，在我们的计算中受到约束，但仍然是自由的。我们还介绍了磁性大气中 Ca 分布的三维计算。我们质疑系统搜索静态解（通常要经过漫长的演化过程才能达到）的意义，我们注意到在分层建立的瞬态阶段会出现显著的行为。
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Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202450634
M. Lippi, L. Ferellec, C. Opitom, S. Faggi, M. Mumma, G. L. Villanueva
We report on the composition of comet C/2023 H2 (Lemmon) (hereafter C/2023 H2) as measured with CRIRES$^+$ at VLT/ESO, under the Director Discretionary Time program: 2112.C-5015. We observed C/2023 H2 between November 24 and 27, 2023, after perihelion and during its close approach to Earth. We used three settings sampling the spectral region from approx 2.5 to 5 mu m, to search for fluorescence emission lines of H$_2$O, HCN, C$_2$H$_2$, NH$_3$, C$_2$H$_6$, H$_2$CO, CH$_3$OH, CH$_4$, and CO. C/2023 H2 spectra are dominated by signatures from hyper-volatile species, namely CO, C$_2$H$_6$, and CH$_4$, while it is particularly difficult to identify lines from less volatile species such as water or methanol. When compared to other comets, C/2023 H2 has an overall typical-to-enriched composition, with CO showing one of the highest infrared values reported so far in Solar System comets within 2 au from the Sun. In this respect, C/2023 H2 shares many similarities with C/2013 R1 (Lovejoy), C/2009 P1 (Garrad), and C/1999 T1 (McNaught-Hartley), although still being rather unique. Results from the analysis of optical spectra (approx 300 to 650 nm) obtained on November 16, 2023, using the Intermediate Dispersion Spectrograph at the Isaac Newton Telescopes are consistent with the infrared ones. Assuming that the composition of C/2023 H2 is original, this comet most likely formed in a region of the disc where CO was particularly enriched, or it could have been captured from other planetary systems forming in the Sun's birth cluster. Similarities with a few other comets suggest the existence of a sub-class of CO-enriched comets, which may be currently under-sampled. Alternatively, water sublimation may have been ineffective due to the presence of a thick dust mantle covering the nucleus surface.
{"title":"The chemical composition of CO-rich comet C/2023 H2 (Lemmon)","authors":"M. Lippi, L. Ferellec, C. Opitom, S. Faggi, M. Mumma, G. L. Villanueva","doi":"10.1051/0004-6361/202450634","DOIUrl":"https://doi.org/10.1051/0004-6361/202450634","url":null,"abstract":"We report on the composition of comet C/2023 H2 (Lemmon) (hereafter C/2023 H2) as measured with CRIRES$^+$ at VLT/ESO, under the Director Discretionary Time program: 2112.C-5015. We observed C/2023 H2 between November 24 and 27, 2023, after perihelion and during its close approach to Earth. We used three settings sampling the spectral region from approx 2.5 to 5 mu m, to search for fluorescence emission lines of H$_2$O, HCN, C$_2$H$_2$, NH$_3$, C$_2$H$_6$, H$_2$CO, CH$_3$OH, CH$_4$, and CO. C/2023 H2 spectra are dominated by signatures from hyper-volatile species, namely CO, C$_2$H$_6$, and CH$_4$, while it is particularly difficult to identify lines from less volatile species such as water or methanol. When compared to other comets, C/2023 H2 has an overall typical-to-enriched composition, with CO showing one of the highest infrared values reported so far in Solar System comets within 2 au from the Sun. In this respect, C/2023 H2 shares many similarities with C/2013 R1 (Lovejoy), C/2009 P1 (Garrad), and C/1999 T1 (McNaught-Hartley), although still being rather unique. Results from the analysis of optical spectra (approx 300 to 650 nm) obtained on November 16, 2023, using the Intermediate Dispersion Spectrograph at the Isaac Newton Telescopes are consistent with the infrared ones. Assuming that the composition of C/2023 H2 is original, this comet most likely formed in a region of the disc where CO was particularly enriched, or it could have been captured from other planetary systems forming in the Sun's birth cluster. Similarities with a few other comets suggest the existence of a sub-class of CO-enriched comets, which may be currently under-sampled. Alternatively, water sublimation may have been ineffective due to the presence of a thick dust mantle covering the nucleus surface.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"35 11","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141809974","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}
Pub Date : 2024-07-23DOI: 10.1051/0004-6361/202449521
Angelos Valentino, J. Magdalenic
We present the study of two solar eruptive events observed on December 7 2020 and October 28 2021. Both events were associated with full halo coronal mass ejections (CMEs) and flares. These events were chosen because they show a strong non-radial direction of propagation in the low corona and their main propagation direction observed in the inner heliosphere is not fully aligned with the Sun-Earth line. This characteristic makes them suitable for our study, which aims to inspect how the non-radial direction of propagation in the low corona affects the time of CMEs' arrival at Earth. We reconstructed the CMEs using SOHO/LASCO and STEREO/COR observations and modelled them with the 3D MHD model EUHFORIA and the cone model for CMEs. In order to compare the accuracy of forecasting the CME and the CME-driven shock arrival time at Earth obtained from different methods, we also used so-called type II bursts, radio signatures of associated shocks, to find the velocities of the CME-driven shocks and forecast the time of their arrival at Earth. Additionally, we estimated the CME arrival time using the 2D CME velocity obtained from the white light images. Our results show that the lowest accuracy of estimated CME Earth arrival times is found when the 2D CME velocity is used (time difference between observed and modelled arrival time, Delta t approx -29 h and -39 h, for the two studied events, respectively). The velocity of the type II radio bursts provides somewhat better — but still not very accurate — results (Delta t approx +21 h and -29 h, for the two studied events, respectively). Employing, as an input to EUHFORIA, the CME parameters obtained from the graduated cylindrical shell (GCS) fittings at consequently increasing heights, results in a strongly improved accuracy of the modelled CME and shock arrival time; Delta t changes from 20 h to 10 min in the case of the first event, and from 12 h to 30 min in the case of the second one. This improvement shows that when we increased the heights of the GCS reconstruction we accounted for the change in the propagation direction of the studied CMEs, which allowed us to accurately model the CME flank encounter at Earth. Our results show the great importance of the change in the direction of propagation of the CME in the low corona when modelling CMEs and estimating the time of their arrival at Earth.
我们介绍了对 2020 年 12 月 7 日和 2021 年 10 月 28 日观测到的两次太阳爆发事件的研究。这两个事件都与全晕日冕物质抛射（CMEs）和耀斑有关。之所以选择这两个事件，是因为它们在低日冕中显示出强烈的非径向传播方向，而且在日光层内部观测到的主要传播方向与日地线并不完全一致。这一特点使它们适合我们的研究，我们的研究旨在考察低日冕中的非径向传播方向如何影响 CME 到达地球的时间。我们利用 SOHO/LASCO 和 STEREO/COR 的观测数据重建了 CMEs，并利用三维 MHD 模型 EUHFORIA 和 CMEs 锥体模型对其进行了模拟。为了比较用不同方法预测 CME 和 CME 驱动的冲击波到达地球时间的准确性，我们还利用所谓的 II 型爆发（相关冲击波的无线电特征）来寻找 CME 驱动的冲击波的速度并预测其到达地球的时间。此外，我们还利用从白光图像中获得的二维 CME 速度来估计 CME 到达时间。结果表明，使用二维 CME 速度估算 CME 到达地球时间的准确性最低（两个研究事件的观测到达时间与模拟到达时间的时间差 Delta t 分别约为 -29 h 和 -39 h）。用 II 型射电暴的速度得出的结果要好一些，但仍然不是很准确（两个研究事件的 Delta t 分别约为 +21 h 和 -29 h）。将从渐变圆柱壳（GCS）试样中获得的 CME 参数作为 EUHFORIA 的输入，在高度上不断增加，结果大大提高了模拟 CME 和冲击到达时间的准确性；在第一个事件中，Delta t 从 20 h 变为 10 min，在第二个事件中，Delta t 从 12 h 变为 30 min。这一改进表明，当我们增加全球气候观测系统重建的高度时，我们考虑到了所研究的 CME 传播方向的变化，这使我们能够准确地模拟 CME 在地球侧面的遭遇。我们的结果表明，在模拟 CME 和估计其到达地球的时间时，CME 在低日冕中传播方向的变化非常重要。
{"title":"Modelling non-radially propagating coronal mass ejections and forecasting the time of their arrival at Earth","authors":"Angelos Valentino, J. Magdalenic","doi":"10.1051/0004-6361/202449521","DOIUrl":"https://doi.org/10.1051/0004-6361/202449521","url":null,"abstract":"We present the study of two solar eruptive events observed on December 7 2020 and October 28 2021. Both events were associated with full halo coronal mass ejections (CMEs) and flares. These events were chosen because they show a strong non-radial direction of propagation in the low corona and their main propagation direction observed in the inner heliosphere is not fully aligned with the Sun-Earth line. This characteristic makes them suitable for our study, which aims to inspect how the non-radial direction of propagation in the low corona affects the time of CMEs' arrival at Earth. We reconstructed the CMEs using SOHO/LASCO and STEREO/COR observations and modelled them with the 3D MHD model EUHFORIA and the cone model for CMEs. \u0000In order to compare the accuracy of forecasting the CME and the CME-driven shock arrival time at Earth obtained from different methods, we also used so-called type II bursts, radio signatures of associated shocks, to find the velocities of the CME-driven shocks and forecast the time of their arrival at Earth. Additionally, we estimated the CME arrival time using the 2D CME velocity obtained from the white light images. \u0000\u0000Our results show that the lowest accuracy of estimated CME Earth arrival times is found when the 2D CME velocity is used (time difference between observed and modelled arrival time, Delta t approx -29 h and -39 h, for the two studied events, respectively). The velocity of the type II radio bursts provides somewhat better — but still not very accurate — results (Delta t approx +21 h and -29 h, for the two studied events, respectively). Employing, as an input to EUHFORIA, the CME parameters obtained from the graduated cylindrical shell (GCS) fittings at consequently increasing heights, results in a strongly improved accuracy of the modelled CME and shock arrival time; Delta t changes from 20 h to 10 min in the case of the first event, and from 12 h to 30 min in the case of the second one. \u0000This improvement shows that when we increased the heights of the GCS reconstruction we accounted for the change in the propagation direction of the studied CMEs, which allowed us to accurately model the CME flank encounter at Earth. \u0000Our results show the great importance of the change in the direction of propagation of the CME in the low corona when modelling CMEs and estimating the time of their arrival at Earth.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"20 10","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141813882","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}
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