Pub Date : 2025-12-08DOI: 10.1051/0004-6361/202557636
O. E. Hernández Alvarez, D. Rednyk, Š. Roučka, P. Dohnal, R. Plašil, J. Glosík
Aims. We investigate whether the nuclear-spin state of H2 (ortho or para state) modifies the kinetics of two key reactions in ammonia formation in the interstellar medium: NH2+ + H2 → NH3+ + H and NH3+ + H2 → NH4+ + H.Methods. The reaction rate coefficients were measured in a cryogenic 22-pole radiofrequency ion trap over 15-270 K using normal H2 (ortho-to-para ratio 3 : 1) and para-enriched H2 (99.5% para-H2) produced by catalytic conversion at ≈15 K.Results. For NH2+ + H2, the reaction rate coefficients are in the range 10−10-10−9 cm3 s−1 with a weak negative temperature dependence. For NH3+ + H2, the reaction rate coefficients exhibit an Arrhenius dependence with an activation energy of ≈90 meV at high temperatures (>100 K), combined with an increasing value towards low temperatures (10-100 K) due to quantum tunneling. In the studied range of temperatures, the reaction rate coefficients obtained with para-enriched and normal H2 are indistinguishable within the experimental uncertainty for both reactions.
{"title":"Nuclear spin effects in ammonia chemistry","authors":"O. E. Hernández Alvarez, D. Rednyk, Š. Roučka, P. Dohnal, R. Plašil, J. Glosík","doi":"10.1051/0004-6361/202557636","DOIUrl":"https://doi.org/10.1051/0004-6361/202557636","url":null,"abstract":"<i>Aims.<i/> We investigate whether the nuclear-spin state of H<sub>2<sub/> (ortho or para state) modifies the kinetics of two key reactions in ammonia formation in the interstellar medium: NH<sub>2<sub/><sup>+<sup/> + H<sub>2<sub/> → NH<sub>3<sub/><sup>+<sup/> + H and NH<sub>3<sub/><sup>+<sup/> + H<sub>2<sub/> → NH<sub>4<sub/><sup>+<sup/> + H.<i>Methods.<i/> The reaction rate coefficients were measured in a cryogenic 22-pole radiofrequency ion trap over 15-270 K using normal H<sub>2<sub/> (ortho-to-para ratio 3 : 1) and para-enriched H<sub>2<sub/> (99.5% para-H<sub>2<sub/>) produced by catalytic conversion at ≈15 K.<i>Results.<i/> For NH<sub>2<sub/><sup>+<sup/> + H<sub>2<sub/>, the reaction rate coefficients are in the range 10<sup>−10<sup/>-10<sup>−9<sup/> cm<sup>3<sup/> s<sup>−1<sup/> with a weak negative temperature dependence. For NH<sub>3<sub/><sup>+<sup/> + H<sub>2<sub/>, the reaction rate coefficients exhibit an Arrhenius dependence with an activation energy of ≈90 meV at high temperatures (>100 K), combined with an increasing value towards low temperatures (10-100 K) due to quantum tunneling. In the studied range of temperatures, the reaction rate coefficients obtained with para-enriched and normal H<sub>2<sub/> are indistinguishable within the experimental uncertainty for both reactions.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"11 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697379","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}
Pub Date : 2025-12-08DOI: 10.1051/0004-6361/202556490
Lucía Bravo Ferres, Francisco Nogueras-Lara, Rainer Schödel, Rubén Fedriani, Adam Ginsburg, Samuel Crowe, Jonathan C. Tan, Morten Andersen, Joseph Armstrong, Yu Cheng, Zhi-Yun Li
Context. Determining the infrared extinction curve towards the Galactic centre is crucial for accurately correcting observed data and deriving the underlying stellar populations. However, extinction curves reported in the literature often show discrepancies.Aims. We aim to derive the infrared extinction curve towards the Galactic centre based on JWST-NIRCam data for the first time, using observations of the Sagittarius C region in the 1-5 μm range.Methods. We determined extinction ratios using two different methods, both based on measuring the reddening vector using the slope of red clump stars (whose intrinsic properties are well known) in observed colour-magnitude diagrams.Results. The extinction curve derived in this work is in good agreement with previous results in the literature. We obtained the following extinction ratios relative to F162M: AFII5W : AF162M : AF182M : AF212N : AF360M : AF405N : AF47ON : AF48OM = 1.84 ± 0.03 : 1.00 : 0.789 ± 0.005 : 0.607 ± 0.014 : 0.306 ± 0.011 : 0.248 ± 0.017 : 0.240 ± 0.019 : 0.21 ± 0.03. Additionally, we found different values of the extinction index for the short- (λ ~ 1-2.5 μm, α ~ 2) and long-wavelength (λ ~ 2.5-5 μm, α ~ 1.4) regimes, with the extinction curve flattening at longer wavelengths. Comparison with extinction curves derived both inside and outside the Galactic centre suggests that the infrared extinction curve does not significantly vary in the central regions, and shows no significant evidence of variations between different lines of sight beyond the inner Galaxy within the uncertainties.
{"title":"The JWST-NIRCam view of Sagittarius C","authors":"Lucía Bravo Ferres, Francisco Nogueras-Lara, Rainer Schödel, Rubén Fedriani, Adam Ginsburg, Samuel Crowe, Jonathan C. Tan, Morten Andersen, Joseph Armstrong, Yu Cheng, Zhi-Yun Li","doi":"10.1051/0004-6361/202556490","DOIUrl":"https://doi.org/10.1051/0004-6361/202556490","url":null,"abstract":"<i>Context.<i/> Determining the infrared extinction curve towards the Galactic centre is crucial for accurately correcting observed data and deriving the underlying stellar populations. However, extinction curves reported in the literature often show discrepancies.<i>Aims.<i/> We aim to derive the infrared extinction curve towards the Galactic centre based on JWST-NIRCam data for the first time, using observations of the Sagittarius C region in the 1-5 μm range.<i>Methods.<i/> We determined extinction ratios using two different methods, both based on measuring the reddening vector using the slope of red clump stars (whose intrinsic properties are well known) in observed colour-magnitude diagrams.<i>Results.<i/> The extinction curve derived in this work is in good agreement with previous results in the literature. We obtained the following extinction ratios relative to F162M: <i>A<i/><sub>FII5W<sub/> : <i>A<i/><sub>F162M<sub/> : <i>A<i/><sub>F182M<sub/> : <i>A<i/><sub>F212N<sub/> : <i>A<i/><sub>F360M<sub/> : <i>A<i/><sub>F405N<sub/> : <i>A<i/><sub>F47ON<sub/> : <i>A<i/><sub>F48OM<sub/> = 1.84 ± 0.03 : 1.00 : 0.789 ± 0.005 : 0.607 ± 0.014 : 0.306 ± 0.011 : 0.248 ± 0.017 : 0.240 ± 0.019 : 0.21 ± 0.03. Additionally, we found different values of the extinction index for the short- (λ ~ 1-2.5 μm, <i>α<i/> ~ 2) and long-wavelength (λ ~ 2.5-5 μm, <i>α<i/> ~ 1.4) regimes, with the extinction curve flattening at longer wavelengths. Comparison with extinction curves derived both inside and outside the Galactic centre suggests that the infrared extinction curve does not significantly vary in the central regions, and shows no significant evidence of variations between different lines of sight beyond the inner Galaxy within the uncertainties.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"11 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697395","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}
Pub Date : 2025-12-05DOI: 10.1051/0004-6361/202557825
T. Liimets, D. P. K. Banerjee, M. Santander-García, J. Alcolea, S. B. Howell, U. Munari, B. Deshev, C. E. Woodward, A. Evans, E. Furlan, T. R. Geballe, R. D. Gehrz, V. Joshi, N. Scott, S. Starrfield
Context. R Aquarii (R Aqr) is a well-known symbiotic binary that attracted renewed interest during its recent periastron passage, an event that occurs only once every ∼40 years. This passage marks the first to be observed with modern, state-of-the-art instruments.Aims We investigated the inner, sub-arcsecond active region of R Aqr during this recent periastron passage, with the goal of gaining insight into the jet-launching mechanisms at work in this system.Methods. We analysed Hα speckle interferometric images obtained one month apart using Fourier techniques. These are complemented by high-resolution optical spectra in the same emission line.Results. Our speckle imaging reveals a newborn two-sided jet orientated in the north–south direction. Its proper motion, 66 ± 19 mas yr−1, confirms that it was launched around 2020 January 7, at the onset of the periastron passage. Further analysis of the elongated central structure reveals a knot in the southern counterpart of the jet moving away from the binary with μ = 27 ± 17 mas yr−1 at a position angle of 187° and an ejection time around 2019 October 28. This interpretation is further supported by our high-resolution spectroscopic data. In addition, we update the expansion parallax distance of R Aqr to 260 pc.
上下文。水瓶座R （R Aqr）是一个众所周知的共生双星，最近在它的近天轨道上引起了新的兴趣，这种事件每隔~ 40年才发生一次。这个通道标志着第一个用现代最先进的仪器观察到的通道。我们研究了raqr的内部亚弧秒活跃区域，以期深入了解该系统中工作的喷射发射机制。我们使用傅里叶技术分析了间隔一个月获得的Hα散斑干涉图像。这些是在同一发射线上的高分辨率光谱的补充。我们的散斑成像显示一个新生的朝南北方向的双面喷流。它的固有运动为66±19 mas yr - 1，这证实了它是在2020年1月7日左右发射的，也就是在近日通道开始的时候。对拉长的中心结构的进一步分析显示，喷流的南部对应部分有一个结，以μ = 27±17 mas yr - 1的速度以187°的位角远离双星，喷射时间约为2019年10月28日。我们的高分辨率光谱数据进一步支持了这一解释。此外，我们将raqr的膨胀视差距离更新为260pc。
{"title":"Newborn jet in the symbiotic system R Aquarii","authors":"T. Liimets, D. P. K. Banerjee, M. Santander-García, J. Alcolea, S. B. Howell, U. Munari, B. Deshev, C. E. Woodward, A. Evans, E. Furlan, T. R. Geballe, R. D. Gehrz, V. Joshi, N. Scott, S. Starrfield","doi":"10.1051/0004-6361/202557825","DOIUrl":"https://doi.org/10.1051/0004-6361/202557825","url":null,"abstract":"<i>Context.<i/> R Aquarii (R Aqr) is a well-known symbiotic binary that attracted renewed interest during its recent periastron passage, an event that occurs only once every ∼40 years. This passage marks the first to be observed with modern, state-of-the-art instruments.<i>Aims<i/> We investigated the inner, sub-arcsecond active region of R Aqr during this recent periastron passage, with the goal of gaining insight into the jet-launching mechanisms at work in this system.<i>Methods.<i/> We analysed H<i>α<i/> speckle interferometric images obtained one month apart using Fourier techniques. These are complemented by high-resolution optical spectra in the same emission line.<i>Results.<i/> Our speckle imaging reveals a newborn two-sided jet orientated in the north–south direction. Its proper motion, 66 ± 19 mas yr<sup>−1<sup/>, confirms that it was launched around 2020 January 7, at the onset of the periastron passage. Further analysis of the elongated central structure reveals a knot in the southern counterpart of the jet moving away from the binary with <i>μ<i/> = 27 ± 17 mas yr<sup>−1<sup/> at a position angle of 187° and an ejection time around 2019 October 28. This interpretation is further supported by our high-resolution spectroscopic data. In addition, we update the expansion parallax distance of R Aqr to 260 pc.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"110 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697374","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}
Pub Date : 2025-12-05DOI: 10.1051/0004-6361/202557422
XueGuang Zhang
In this work, we use variations in optical spectral index, α5100, to detect central sub-parsec binary black hole systems (sub-pc BBHs) in broad line active galactic nuclei (BLAGNs) through apparent effects of obscurations on two central BH accreting systems. For sub-pc BBHs in BLAGNs, two main characteristics of α5100 can be expected. First, if a BLAGN harbours a central sub-pc BBH, the expected unique variability in α5100 should lead to the BLAGN being an outlier in the space of α5100 versus continuum luminosity, L5100, determined from normal BLAGNs. Second, BLAGNs harbouring central sub-pc BBHs can lead to periodic variations in α5100. Here, after checking the two-epoch Sloan Digital Sky Survey (SDSS) spectra of quasar SDSS J0012-1022 reported as a candidate of sub-pc BBH by a large velocity offset between narrow and broad Balmer emission lines, the unique variability of α5100 can be explained by the effects of obscurations related to an assumed central sub-pc BBH. The results of this work provide a new method of detecting sub-pc BBHs in BLAGNs through the application of properties of optical continuum emissions. In the near future, detecting and reporting periodic variations of α5100 for sub-pc BBHs in BLAGNs should be main objective of our research group.
{"title":"Variability of optical spectral index to support a central sub-parsec binary black hole system in quasar SDSS J001224-102226.51","authors":"XueGuang Zhang","doi":"10.1051/0004-6361/202557422","DOIUrl":"https://doi.org/10.1051/0004-6361/202557422","url":null,"abstract":"In this work, we use variations in optical spectral index, <i>α<i/><sub>5100<sub/>, to detect central sub-parsec binary black hole systems (sub-pc BBHs) in broad line active galactic nuclei (BLAGNs) through apparent effects of obscurations on two central BH accreting systems. For sub-pc BBHs in BLAGNs, two main characteristics of <i>α<i/><sub>5100<sub/> can be expected. First, if a BLAGN harbours a central sub-pc BBH, the expected unique variability in <i>α<i/><sub>5100<sub/> should lead to the BLAGN being an outlier in the space of <i>α<i/><sub>5100<sub/> versus continuum luminosity, <i>L<i/><sub>5100<sub/>, determined from normal BLAGNs. Second, BLAGNs harbouring central sub-pc BBHs can lead to periodic variations in <i>α<i/><sub>5100<sub/>. Here, after checking the two-epoch Sloan Digital Sky Survey (SDSS) spectra of quasar SDSS J0012-1022 reported as a candidate of sub-pc BBH by a large velocity offset between narrow and broad Balmer emission lines, the unique variability of <i>α<i/><sub>5100<sub/> can be explained by the effects of obscurations related to an assumed central sub-pc BBH. The results of this work provide a new method of detecting sub-pc BBHs in BLAGNs through the application of properties of optical continuum emissions. In the near future, detecting and reporting periodic variations of <i>α<i/><sub>5100<sub/> for sub-pc BBHs in BLAGNs should be main objective of our research group.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"3 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697375","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}
Pub Date : 2025-12-05DOI: 10.1051/0004-6361/202556879
Alessandro Bruno, Melissa Pesce-Rollins, Silvia Dalla, Nicola Omodei, Ian G. Richardson, James M. Ryan
We present a multi-spacecraft analysis of the 2024 July 16 long-duration gamma-ray flare (LDGRF) detected by the Large Area Telescope on the Fermi satellite. The measured > 100 MeV γ-ray emission persisted for over seven hours after the flare impulsive phase, and was characterized by photon energies exceeding 1 GeV and a remarkably hard parent-proton spectrum. In contrast, the phenomena related to the coronal mass ejection (CME)-driven shock linked to this eruption were modest, suggesting an inefficient proton acceleration unlikely to achieve energies well above the 300 MeV pion-production threshold to account for the observed γ-ray emission. Specifically, the CME was relatively slow (∼600 km/s) and the accompanying interplanetary type-II/III radio bursts were faint and short-lived, unlike those typically detected during large events. In particular, the type-II emission did not extend to kilohertz frequencies and disappeared ∼5.5 hours prior to the LDGRF end time. Furthermore, the associated solar energetic particle (SEP) event was very weak, short-duration, and limited to a few tens of MeV, even at magnetically well-connected spacecraft. These findings demonstrate that a very fast CME resulting in a high-energy SEP event is not a necessary condition for the occurrence of LDGRFs, challenging the idea that the high-energy γ-ray emission is produced by the back-precipitation of shock-accelerated ions into the solar surface. The alternative origin scenario based on local particle trapping and acceleration in large-scale coronal loops is instead favored by the observation of giant arch-like structures of hot plasma over the source region that persisted for the entire duration of this LDGRF.
{"title":"The 2024 July 16 solar event: a challenge to the coronal mass ejection origin of long-duration gamma-ray flares","authors":"Alessandro Bruno, Melissa Pesce-Rollins, Silvia Dalla, Nicola Omodei, Ian G. Richardson, James M. Ryan","doi":"10.1051/0004-6361/202556879","DOIUrl":"https://doi.org/10.1051/0004-6361/202556879","url":null,"abstract":"We present a multi-spacecraft analysis of the 2024 July 16 long-duration gamma-ray flare (LDGRF) detected by the Large Area Telescope on the <i>Fermi<i/> satellite. The measured > 100 MeV <i>γ<i/>-ray emission persisted for over seven hours after the flare impulsive phase, and was characterized by photon energies exceeding 1 GeV and a remarkably hard parent-proton spectrum. In contrast, the phenomena related to the coronal mass ejection (CME)-driven shock linked to this eruption were modest, suggesting an inefficient proton acceleration unlikely to achieve energies well above the 300 MeV pion-production threshold to account for the observed <i>γ<i/>-ray emission. Specifically, the CME was relatively slow (∼600 km/s) and the accompanying interplanetary type-II/III radio bursts were faint and short-lived, unlike those typically detected during large events. In particular, the type-II emission did not extend to kilohertz frequencies and disappeared ∼5.5 hours prior to the LDGRF end time. Furthermore, the associated solar energetic particle (SEP) event was very weak, short-duration, and limited to a few tens of MeV, even at magnetically well-connected spacecraft. These findings demonstrate that a very fast CME resulting in a high-energy SEP event is not a necessary condition for the occurrence of LDGRFs, challenging the idea that the high-energy <i>γ<i/>-ray emission is produced by the back-precipitation of shock-accelerated ions into the solar surface. The alternative origin scenario based on local particle trapping and acceleration in large-scale coronal loops is instead favored by the observation of giant arch-like structures of hot plasma over the source region that persisted for the entire duration of this LDGRF.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"61 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697378","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}
Pub Date : 2025-12-05DOI: 10.1051/0004-6361/202555453
Sergio A. Dzib, Frederic Jaron
The binary star MWC 656 was initially proposed as the first confirmed system composed of a Be star and a black hole (BH). However, recent studies have challenged this interpretation, suggesting that the compact companion is unlikely to be a BH. In this study, we revisited the nature of MWC 656 by analyzing archival data across multiple wavelengths, including radio observations from the Karl G. Jansky Very Large Array (VLA), optical astrometry from the Gaia satellite, and high-energy γ-ray data from the Fermi-LAT. Using all available VLA observations at the X band (8.0−12.0 GHz), we produced the deepest radio map toward this system to date, with a noise level of 780 nJy beam−1. The source MWC 656 was detected with Sν = 4.6 ± 0.8 μJy and a spectral index of α = 1.2 ± 1.8, derived by sub-band imaging. The radio-X-ray-luminosity ratio of MWC 656 is consistent with both the fundamental plane of accreting BHs and with the Güdel-Benz relation for magnetically active stars, leaving the emission mechanism ambiguous. The optical astrometric results of MWC 656 indicate a peculiar velocity of 11.2 ± 2.3 km s−1, discarding it as a runaway star. Its current location, 442 pc below the Galactic plane, implies a vertical travel time incompatible with the lifetime of a B1.5-type star. Moreover, the agreement between observed and expected motion in all three velocity components argues against a deceleration scenario, suggesting that MWC 656 likely formed in situ at high Galactic latitudes. We carried out a maximum-likelihood analysis of Fermi-LAT data, but we cannot report a significant detection of γ-ray emission from this source. These results reinforce recent evidence that challenge the BH companion interpretation, and favor a non-BH compact object such as a white dwarf or neutron star.
{"title":"Constraining the nature and Galactic origin of the Be binary MWC 656","authors":"Sergio A. Dzib, Frederic Jaron","doi":"10.1051/0004-6361/202555453","DOIUrl":"https://doi.org/10.1051/0004-6361/202555453","url":null,"abstract":"The binary star MWC 656 was initially proposed as the first confirmed system composed of a Be star and a black hole (BH). However, recent studies have challenged this interpretation, suggesting that the compact companion is unlikely to be a BH. In this study, we revisited the nature of MWC 656 by analyzing archival data across multiple wavelengths, including radio observations from the <i>Karl G. Jansky<i/> Very Large Array (VLA), optical astrometry from the <i>Gaia<i/> satellite, and high-energy <i>γ<i/>-ray data from the <i>Fermi<i/>-LAT. Using all available VLA observations at the X band (8.0−12.0 GHz), we produced the deepest radio map toward this system to date, with a noise level of 780 nJy beam<sup>−1<sup/>. The source MWC 656 was detected with <i>S<i/><sub><i>ν<i/><sub/> = 4.6 ± 0.8 μJy and a spectral index of <i>α<i/> = 1.2 ± 1.8, derived by sub-band imaging. The radio-X-ray-luminosity ratio of MWC 656 is consistent with both the fundamental plane of accreting BHs and with the Güdel-Benz relation for magnetically active stars, leaving the emission mechanism ambiguous. The optical astrometric results of MWC 656 indicate a peculiar velocity of 11.2 ± 2.3 km s<sup>−1<sup/>, discarding it as a runaway star. Its current location, 442 pc below the Galactic plane, implies a vertical travel time incompatible with the lifetime of a B1.5-type star. Moreover, the agreement between observed and expected motion in all three velocity components argues against a deceleration scenario, suggesting that MWC 656 likely formed in situ at high Galactic latitudes. We carried out a maximum-likelihood analysis of <i>Fermi<i/>-LAT data, but we cannot report a significant detection of <i>γ<i/>-ray emission from this source. These results reinforce recent evidence that challenge the BH companion interpretation, and favor a non-BH compact object such as a white dwarf or neutron star.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"5 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697381","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}
Pub Date : 2025-12-05DOI: 10.1051/0004-6361/202557289
Fabrizio Tavecchio
The VERITAS Collaboration recently reported the detection of very high-energy (VHE) gamma-ray emission from the prototypical radio quasar 3C273. The temporal and spectral properties of this component do not appear compatible with the extrapolation of the beamed blazar-like emission of the inner, parsec-scale jet. We explore the possibility that the VHE component is produced in the jet at kiloparsec scales through the inverse Compton emission of a population of ultra-high-energy electrons (with Lorentz factor γ ∼ 108). In the model these electrons are accelerated through the shear acceleration mechanism, and they account for the still puzzling X-ray emission of knots detected by Chandra in the large-scale jets of several powerful quasars (including 3C273). In our scenario, the VHE component can be interpreted as the integrated emission from the two brightest knots of the 3C273 jet. We speculate that the decay of the emission on a timescale of ∼3 years could be accounted for by the scenario if the VHE radiation is produced in some compact regions in the downstream flow of a recollimation shock.
{"title":"The TeV emission of 3C273: Inverse Compton radiation from shear-accelerated high-energy electrons in the large-scale jet?","authors":"Fabrizio Tavecchio","doi":"10.1051/0004-6361/202557289","DOIUrl":"https://doi.org/10.1051/0004-6361/202557289","url":null,"abstract":"The VERITAS Collaboration recently reported the detection of very high-energy (VHE) gamma-ray emission from the prototypical radio quasar 3C273. The temporal and spectral properties of this component do not appear compatible with the extrapolation of the beamed blazar-like emission of the inner, parsec-scale jet. We explore the possibility that the VHE component is produced in the jet at kiloparsec scales through the inverse Compton emission of a population of ultra-high-energy electrons (with Lorentz factor <i>γ<i/> ∼ 10<sup>8<sup/>). In the model these electrons are accelerated through the shear acceleration mechanism, and they account for the still puzzling X-ray emission of knots detected by <i>Chandra<i/> in the large-scale jets of several powerful quasars (including 3C273). In our scenario, the VHE component can be interpreted as the integrated emission from the two brightest knots of the 3C273 jet. We speculate that the decay of the emission on a timescale of ∼3 years could be accounted for by the scenario if the VHE radiation is produced in some compact regions in the downstream flow of a recollimation shock.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"30 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697376","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}
Pub Date : 2025-12-05DOI: 10.1051/0004-6361/202557288
Deboki Reja, Paul S. Barklem, Stan Bartmentloo, Anders Jerkstrand
The charge-transfer process C + O+ → C+ + O (1D) has been found in previous modelling to be important in neutralising oxygen ions in supernova (SN) ejecta, as well as in determining the strength of the [O I] doublet at 6300 and 6364 Å. This conclusion is, however, based on a highly uncertain simple estimate of the rate coefficient. In this work, calculations of the cross-sections at low energy (0–10 eV) are performed using quantum mechanical methods. The rate coefficients at temperatures up to 10 000 K are determined and found to be significantly lower than the simple estimate. Using spectral modelling of SN ejecta, we show that the new rates change model predictions for [O I] λλ6300, 6364 and [C I] λλ9824, 9850 by ~10% in the early, warm nebular phases, and by yet larger factors in the late, cold phases, with direct impact on inferences of carbon and oxygen masses.
{"title":"Charge transfer in C + O+ collisions and its impact on supernova spectra","authors":"Deboki Reja, Paul S. Barklem, Stan Bartmentloo, Anders Jerkstrand","doi":"10.1051/0004-6361/202557288","DOIUrl":"https://doi.org/10.1051/0004-6361/202557288","url":null,"abstract":"The charge-transfer process C + O<sup>+<sup/> → C<sup>+<sup/> + O (<sup>1<sup/>D) has been found in previous modelling to be important in neutralising oxygen ions in supernova (SN) ejecta, as well as in determining the strength of the [O I] doublet at 6300 and 6364 Å. This conclusion is, however, based on a highly uncertain simple estimate of the rate coefficient. In this work, calculations of the cross-sections at low energy (0–10 eV) are performed using quantum mechanical methods. The rate coefficients at temperatures up to 10 000 K are determined and found to be significantly lower than the simple estimate. Using spectral modelling of SN ejecta, we show that the new rates change model predictions for [O I] <i>λλ<i/>6300, 6364 and [C I] <i>λλ<i/>9824, 9850 by ~10% in the early, warm nebular phases, and by yet larger factors in the late, cold phases, with direct impact on inferences of carbon and oxygen masses.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"11 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697372","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}
Pub Date : 2025-12-03DOI: 10.1051/0004-6361/202557059
C. E. Scardoni, G. P. Rosotti, C. J. Clarke, E. Ragusa, R. A. Booth
Context. Recent studies on the planet-dominated regime of type II migration have demonstrated the presence of a correlation between the direction of massive planet migration and the parameter K that describes the depth of the gap opened by the planet. Indeed, it has been reported that high (low) values for the K parameter correspond to an outward (inward) migration.Aims. In this paper, we aim to understand the mechanism driving inward and outward migration and why these mechanisms are correlated with the gap depth.Methods. We performed a suite of 2D, live-planet, long-term simulations of massive planets migrating in disks with the hydro-code FARGO3D. We focused on a range of planet masses (1–13 mJ) and disk aspect ratios (from 0.03 to 0.1). We analyzed the evolution of orbital elements and gap structure. We also studied the torque contributions from outer Lindblad resonances to investigate their role in the migration outcome.Results. We find that while all planets initially migrate inward, those with high enough K values eventually enter a phase in which the torque reverses sign and migration turns outward, until the point where it stalls. This behavior is associated with eccentricity growth in the outer disk and changes in the gap structure. We identified the surface density ratio at the 1:2 and 1:3 outer Lindblad resonances as a key output diagnostic that are correlated with the migration direction. In general, this ratio regulates the migration for all the cases where the massive planet remains in an almost circular orbit and the outer gap region exhibits moderate eccentricity. This characteristic sequence of inward-reversal-outward-stalling can occur for a variety of K values. Thus, further work is required to identify the simulation input parameters that determine the onset of this sequence.Conclusions. Our results suggest that outward migration in the planet-dominated regime is primarily governed by the relative importance of the 1:2 and 1:3 resonances. Therefore, the gap profiles play a crucial role in determining the direction of migration.
{"title":"Eccentric disks as a gateway to giant planet outward migration","authors":"C. E. Scardoni, G. P. Rosotti, C. J. Clarke, E. Ragusa, R. A. Booth","doi":"10.1051/0004-6361/202557059","DOIUrl":"https://doi.org/10.1051/0004-6361/202557059","url":null,"abstract":"<i>Context<i/>. Recent studies on the planet-dominated regime of type II migration have demonstrated the presence of a correlation between the direction of massive planet migration and the parameter <i>K<i/> that describes the depth of the gap opened by the planet. Indeed, it has been reported that high (low) values for the <i>K<i/> parameter correspond to an outward (inward) migration.<i>Aims<i/>. In this paper, we aim to understand the mechanism driving inward and outward migration and why these mechanisms are correlated with the gap depth.<i>Methods<i/>. We performed a suite of 2D, live-planet, long-term simulations of massive planets migrating in disks with the hydro-code FARGO3D. We focused on a range of planet masses (1–13 <i>m<i/><sub>J<sub/>) and disk aspect ratios (from 0.03 to 0.1). We analyzed the evolution of orbital elements and gap structure. We also studied the torque contributions from outer Lindblad resonances to investigate their role in the migration outcome.<i>Results<i/>. We find that while all planets initially migrate inward, those with high enough <i>K<i/> values eventually enter a phase in which the torque reverses sign and migration turns outward, until the point where it stalls. This behavior is associated with eccentricity growth in the outer disk and changes in the gap structure. We identified the surface density ratio at the 1:2 and 1:3 outer Lindblad resonances as a key output diagnostic that are correlated with the migration direction. In general, this ratio regulates the migration for all the cases where the massive planet remains in an almost circular orbit and the outer gap region exhibits moderate eccentricity. This characteristic sequence of inward-reversal-outward-stalling can occur for a variety of <i>K<i/> values. Thus, further work is required to identify the simulation input parameters that determine the onset of this sequence.<i>Conclusions<i/>. Our results suggest that outward migration in the planet-dominated regime is primarily governed by the relative importance of the 1:2 and 1:3 resonances. Therefore, the gap profiles play a crucial role in determining the direction of migration.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"4 1","pages":"A78"},"PeriodicalIF":6.5,"publicationDate":"2025-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697207","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}
Pub Date : 2025-12-03DOI: 10.1051/0004-6361/202556757
K. Thomson-Paressant, C. Neiner, J. Labadie-Bartz, R.-M. Ouazzani, S. Mathis, L. Manchon
Context. At this time, the list of known magnetic δ Scuti stars is extremely limited, with only a select number of well-studied examples.Aims. We seek to expand this list, by retrieving targets from a variety of sources and demonstrating that they present simultaneously a surface magnetic field signature and δ Scuti pulsations.Methods. We obtained archival and new spectropolarimetric datasets for a variety of known δ Scuti stars and analysed them using the least squares deconvolution method to generate mean Stokes I and V profiles for each target, from which we can determine longitudinal magnetic field measurements. Additionally, we assessed photometric data from the TESS satellite to discern frequency peaks consistent with δ Scuti pulsations in known magnetic stars, and to identify magnetic candidates via rotational modulation.Results. We present a compiled list of all the confirmed magnetic δ Scuti stars discovered to date, containing 13 stars. The majority of this sample lies outside the usual δ Scuti instability strip in the Hertzsprung-Russell diagram, though we do not observe any specific correlations between magnetic field strength and various stellar parameters. This indicates that strong global magnetic fields play a fundamental role in shaping interior structure and processes. Magnetic fields thus must be included in realistic stellar models in order to more accurately predict structure and evolution.Conclusions. This work constitutes the largest database to date of strongly magnetic δ Scuti stars, one that will continue to grow over time with subsequent studies.
{"title":"Discovery of new magnetic δ Scuti stars and the impact of magnetism on pulsation excitation","authors":"K. Thomson-Paressant, C. Neiner, J. Labadie-Bartz, R.-M. Ouazzani, S. Mathis, L. Manchon","doi":"10.1051/0004-6361/202556757","DOIUrl":"https://doi.org/10.1051/0004-6361/202556757","url":null,"abstract":"<i>Context.<i/> At this time, the list of known magnetic <i>δ<i/> Scuti stars is extremely limited, with only a select number of well-studied examples.<i>Aims.<i/> We seek to expand this list, by retrieving targets from a variety of sources and demonstrating that they present simultaneously a surface magnetic field signature and <i>δ<i/> Scuti pulsations.<i>Methods.<i/> We obtained archival and new spectropolarimetric datasets for a variety of known <i>δ<i/> Scuti stars and analysed them using the least squares deconvolution method to generate mean Stokes <i>I<i/> and <i>V<i/> profiles for each target, from which we can determine longitudinal magnetic field measurements. Additionally, we assessed photometric data from the TESS satellite to discern frequency peaks consistent with <i>δ<i/> Scuti pulsations in known magnetic stars, and to identify magnetic candidates via rotational modulation.<i>Results.<i/> We present a compiled list of all the confirmed magnetic <i>δ<i/> Scuti stars discovered to date, containing 13 stars. The majority of this sample lies outside the usual <i>δ<i/> Scuti instability strip in the Hertzsprung-Russell diagram, though we do not observe any specific correlations between magnetic field strength and various stellar parameters. This indicates that strong global magnetic fields play a fundamental role in shaping interior structure and processes. Magnetic fields thus must be included in realistic stellar models in order to more accurately predict structure and evolution.<i>Conclusions.<i/> This work constitutes the largest database to date of strongly magnetic <i>δ<i/> Scuti stars, one that will continue to grow over time with subsequent studies.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"3 1","pages":"A134"},"PeriodicalIF":6.5,"publicationDate":"2025-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697212","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}
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