Pub Date : 2020-12-11DOI: 10.1051/0004-6361/202039441
F. Lucertini, D. Nardiello, G. Piotto
Aims. We present a new technique to estimate the relative ages of multiple stellar populations hosted by five globular clusters: NGC 104 (47 Tuc), NGC 6121 (M4), NGC 6352, NGC 6362 and NGC 6723. Methods. We used the catalogs of the database "HST UV Globular cluster Survey (HUGS)" to create color-magnitude and two-color diagrams of the Globular Clusters. We identified the multiple populations within each globular cluster, and we divided them into two main stellar populations: POPa or first generation (1G) and POPb, composed of all the successive generations of stars. The new technique allows us to obtain an accurate estimate of the relative ages between POPa and POPb. Results. The multiple populations of NGC 104 and NGC 6121 are coeval within 220 Myr and 214 Myr, while those of NGC 6352, NGC 6362 and NGC 6723 are coeval within 336 Myr, 474 Myr and 634 Myr, respectively. These results were obtained combining all the sources of uncertainties.
目标我们提出了一种新的技术来估计五个球状星团:NGC 104 (47 Tuc)， NGC 6121 (M4)， NGC 6352, NGC 6362和NGC 6723所拥有的多个恒星群的相对年龄。方法。我们使用“HST紫外球状星团调查(HUGS)”数据库的目录来创建球状星团的彩色、星等和双色图。我们确定了每个球状星团内的多个恒星群，并将它们分为两个主要恒星群:POPa或第一代(1G)和POPb，由所有连续几代恒星组成。这项新技术使我们能够准确地估计出POPa和POPb之间的相对年龄。结果。NGC 104和NGC 6121在220 Myr和214 Myr范围内具有相同的种群，NGC 6352、NGC 6362和NGC 6723分别在336 Myr、474 Myr和634 Myr范围内具有相同的种群。这些结果是综合了所有不确定度的来源得到的。
{"title":"The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters","authors":"F. Lucertini, D. Nardiello, G. Piotto","doi":"10.1051/0004-6361/202039441","DOIUrl":"https://doi.org/10.1051/0004-6361/202039441","url":null,"abstract":"Aims. We present a new technique to estimate the relative ages of multiple stellar populations hosted by five globular clusters: NGC 104 (47 Tuc), NGC 6121 (M4), NGC 6352, NGC 6362 and NGC 6723. Methods. We used the catalogs of the database \"HST UV Globular cluster Survey (HUGS)\" to create color-magnitude and two-color diagrams of the Globular Clusters. We identified the multiple populations within each globular cluster, and we divided them into two main stellar populations: POPa or first generation (1G) and POPb, composed of all the successive generations of stars. The new technique allows us to obtain an accurate estimate of the relative ages between POPa and POPb. Results. The multiple populations of NGC 104 and NGC 6121 are coeval within 220 Myr and 214 Myr, while those of NGC 6352, NGC 6362 and NGC 6723 are coeval within 336 Myr, 474 Myr and 634 Myr, respectively. These results were obtained combining all the sources of uncertainties.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86001062","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}
E. Brown, S. Marsden, M. Mengel, S. Jeffers, I. Millburn, M. Mittag, P. Petit, A. Vidotto, J. Morin, V. See, M. Jardine, J. N. Gonz'alez-P'erez
Studying cool star magnetic activity gives an important insight into the stellar dynamo and its relationship with stellar properties, as well as allowing us to place the Sun's magnetism in the context of other stars. Only 61 Cyg A (K5V) and $tau$ Boo (F8V) are currently known to have magnetic cycles like the Sun's, where the large-scale magnetic field polarity reverses in phase with the star's chromospheric activity cycles. ${tau}$ Boo has a rapid $sim$240 d magnetic cycle, and it is not yet clear whether this is related to the star's thin convection zone or if the dynamo is accelerated by interactions between ${tau}$ Boo and its hot Jupiter. To shed light on this, we studied the magnetic activity of HD75332 (F7V) which has similar physical properties to ${tau}$ Boo and does not appear to host a hot Jupiter. We characterized its long term chromospheric activity variability over 53 yrs and used Zeeman Doppler Imaging to reconstruct the large-scale surface magnetic field for 12 epochs between 2007 and 2019. Although we observe only one reversal of the large-scale magnetic dipole, our results suggest that HD75332 has a rapid $sim$1.06 yr solar-like magnetic cycle where the magnetic field evolves in phase with its chromospheric activity. If a solar-like cycle is present, reversals of the large-scale radial field polarity are expected to occur at around activity cycle maxima. This would be similar to the rapid magnetic cycle observed for ${tau}$ Boo, suggesting that rapid magnetic cycles may be intrinsic to late-F stars and related to their shallow convection zones.
{"title":"Magnetic field and chromospheric activity evolution of HD 75332: a rapid magnetic cycle in an F star without a hot Jupiter","authors":"E. Brown, S. Marsden, M. Mengel, S. Jeffers, I. Millburn, M. Mittag, P. Petit, A. Vidotto, J. Morin, V. See, M. Jardine, J. N. Gonz'alez-P'erez","doi":"10.1093/mnras/staa3878","DOIUrl":"https://doi.org/10.1093/mnras/staa3878","url":null,"abstract":"Studying cool star magnetic activity gives an important insight into the stellar dynamo and its relationship with stellar properties, as well as allowing us to place the Sun's magnetism in the context of other stars. Only 61 Cyg A (K5V) and $tau$ Boo (F8V) are currently known to have magnetic cycles like the Sun's, where the large-scale magnetic field polarity reverses in phase with the star's chromospheric activity cycles. ${tau}$ Boo has a rapid $sim$240 d magnetic cycle, and it is not yet clear whether this is related to the star's thin convection zone or if the dynamo is accelerated by interactions between ${tau}$ Boo and its hot Jupiter. To shed light on this, we studied the magnetic activity of HD75332 (F7V) which has similar physical properties to ${tau}$ Boo and does not appear to host a hot Jupiter. We characterized its long term chromospheric activity variability over 53 yrs and used Zeeman Doppler Imaging to reconstruct the large-scale surface magnetic field for 12 epochs between 2007 and 2019. Although we observe only one reversal of the large-scale magnetic dipole, our results suggest that HD75332 has a rapid $sim$1.06 yr solar-like magnetic cycle where the magnetic field evolves in phase with its chromospheric activity. If a solar-like cycle is present, reversals of the large-scale radial field polarity are expected to occur at around activity cycle maxima. This would be similar to the rapid magnetic cycle observed for ${tau}$ Boo, suggesting that rapid magnetic cycles may be intrinsic to late-F stars and related to their shallow convection zones.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82339238","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}
Recent multi-messenger detection of the binary neutron star merger (GW170817) energized the astrophysical community and encouraged further research for determination of nuclear physics observables. Comprehensive studies of atomic nuclei in the cosmos provide an opportunity for investigating these astrophysical phenomena and acquiring complementary information on stellar nucleosynthesis processes that can be verified using the latest nuclear data. Evaluated Nuclear Data File (ENDF) libraries contain complete collections of reaction cross sections over the energy range relevant to astrophysics, fission yields and decay data. These data collections have been used worldwide in nuclear science, industry and national security applications. There is great interest in exploring the ENDF/B-VIII.0 and TALYS Evaluated Nuclear Data Library (TENDL-2015) for nuclear astrophysics purposes and comparing findings with the Karlsruhe Astrophysical Database of Nucleosynthesis in Stars (KADoNiS). The Maxwellian-averaged cross sections (MACS) and astrophysical reaction rates have been calculated using the ENDF/B-VIII.0 and TENDL-2015 evaluated data sets. The calculated cross sections were combined with the solar system abundances and fitted using the classical model of stellar nucleosynthesis. Astrophysical rapid- and slow-neutron capture, $r$- and $s$-process, respectively, abundances were obtained from present data and compared with available values. Further analysis of MACS reveals potential evaluated libraries data deficiencies and a strong need for new measurements. The current results demonstrate a large nuclear astrophysics potential of evaluated libraries and mutually beneficial relations between nuclear industry and research efforts.
{"title":"Determination of Solar System R-Process Abundances using ENDF/B-VIII.0 and TENDL-2015 libraries","authors":"B. Pritychenko","doi":"10.2172/1737434","DOIUrl":"https://doi.org/10.2172/1737434","url":null,"abstract":"Recent multi-messenger detection of the binary neutron star merger (GW170817) energized the astrophysical community and encouraged further research for determination of nuclear physics observables. Comprehensive studies of atomic nuclei in the cosmos provide an opportunity for investigating these astrophysical phenomena and acquiring complementary information on stellar nucleosynthesis processes that can be verified using the latest nuclear data. \u0000Evaluated Nuclear Data File (ENDF) libraries contain complete collections of reaction cross sections over the energy range relevant to astrophysics, fission yields and decay data. These data collections have been used worldwide in nuclear science, industry and national security applications. There is great interest in exploring the ENDF/B-VIII.0 and TALYS Evaluated Nuclear Data Library (TENDL-2015) for nuclear astrophysics purposes and comparing findings with the Karlsruhe Astrophysical Database of Nucleosynthesis in Stars (KADoNiS). \u0000The Maxwellian-averaged cross sections (MACS) and astrophysical reaction rates have been calculated using the ENDF/B-VIII.0 and TENDL-2015 evaluated data sets. The calculated cross sections were combined with the solar system abundances and fitted using the classical model of stellar nucleosynthesis. Astrophysical rapid- and slow-neutron capture, $r$- and $s$-process, respectively, abundances were obtained from present data and compared with available values. Further analysis of MACS reveals potential evaluated libraries data deficiencies and a strong need for new measurements. The current results demonstrate a large nuclear astrophysics potential of evaluated libraries and mutually beneficial relations between nuclear industry and research efforts.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75058610","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 : 2020-12-07DOI: 10.5303/JKAS.2020.53.6.169
Seok-Jun Chang, Hee-Won Lee
Emission features formed through Raman scattering with atomic hydrogen provide unique and crucial information to probe the distribution and kinematics of a thick neutral region illuminated by a strong far UV emission source. We introduce a new 3 dimensional Monte-Carlo code in order to describe the radiative transfer of line photons that are subject to Raman and Rayleigh scattering with atomic hydrogen. In this code entitled "${bf S}$ejong Radiative ${bf T}$r${bf a}$nsfer through ${bf R}$aman and Rayleigh ${bf S}$cattering (${it STaRS}$), each photon is traced until escape with a tag attached carrying information including the position, direction, wavelength, and polarization. The thick neutral scattering region is divided into numerous cells with each cell being characterized by its velocity and density, which ensures huge flexibility of the code in analyzing Raman-scattered features formed in a neutral region with complicated kinematics and density distribution. As a test of the code, we revisit the formation of Balmer wings through Raman scattering of far UV continuum near Ly$beta$ and Ly$gamma$ in a static neutral region. An additional check is made to investigate Raman scattering of O VI in an expanding neutral medium. We find fairly good agreement of our results with previous works, demonstrating the capability of dealing with radiative transfer modeling that can be applied to spectropolarimetric imaging observations of various objects including symbiotic stars, young planetary nebulae, and active galactic nuclei.
{"title":"3D Grid-Based Monte Carlo Code for Radiative Transfer through Raman and Rayleigh Scattering with Atomic Hydrogen -- STaRS","authors":"Seok-Jun Chang, Hee-Won Lee","doi":"10.5303/JKAS.2020.53.6.169","DOIUrl":"https://doi.org/10.5303/JKAS.2020.53.6.169","url":null,"abstract":"Emission features formed through Raman scattering with atomic hydrogen provide unique and crucial information to probe the distribution and kinematics of a thick neutral region illuminated by a strong far UV emission source. We introduce a new 3 dimensional Monte-Carlo code in order to describe the radiative transfer of line photons that are subject to Raman and Rayleigh scattering with atomic hydrogen. In this code entitled \"${bf S}$ejong Radiative ${bf T}$r${bf a}$nsfer through ${bf R}$aman and Rayleigh ${bf S}$cattering (${it STaRS}$), each photon is traced until escape with a tag attached carrying information including the position, direction, wavelength, and polarization. The thick neutral scattering region is divided into numerous cells with each cell being characterized by its velocity and density, which ensures huge flexibility of the code in analyzing Raman-scattered features formed in a neutral region with complicated kinematics and density distribution. As a test of the code, we revisit the formation of Balmer wings through Raman scattering of far UV continuum near Ly$beta$ and Ly$gamma$ in a static neutral region. An additional check is made to investigate Raman scattering of O VI in an expanding neutral medium. We find fairly good agreement of our results with previous works, demonstrating the capability of dealing with radiative transfer modeling that can be applied to spectropolarimetric imaging observations of various objects including symbiotic stars, young planetary nebulae, and active galactic nuclei.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78424044","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}
Sharmila Rani, G. Pandey, A. Subramaniam, S. Sahu, N. Rao
We present the UV photometry of the globular cluster NGC 1261 using images acquired with the Ultraviolet Imaging Telescope (UVIT) on-board ASTROSAT. We performed PSF photometry on four near-UV (NUV) and two far-UV (FUV) images and constructed UV colour-magnitude diagrams (CMDs), in combination with HST, Gaia, and ground-based optical photometry for member stars. We detected the full horizontal branch (HB) in NUV, blue HB in the FUV and identified two extreme HB (EHB) stars. HB stars have a tight sequence in UV-optical CMDs well-fitted with isochrones generated (12.6 Gyr age, [Fe/H] = -1.27 metallicity) using updated BaSTI-IAC models. Effective temperatures (Teff), luminosities and radii of bright HB stars were estimated using spectral energy distribution. As we detect the complete sample of UV bright HB stars, the hot end of the HB distribution is found to terminate at the G-jump (Teff ~ 11500 K). The two EHB stars, fitted well with single spectra, have Teff= 31,000 K and a mass = 0.495Msun and follow the same Teff-Radius relation of the blue HB stars. We constrain the formation pathways of these EHB stars to extreme mass loss in the RGB phase (either due to rotation or enhanced Helium), OR early hot-flash scenario.
{"title":"Study of UV-bright stellar populations in the globular cluster NGC 1261 using Astrosat","authors":"Sharmila Rani, G. Pandey, A. Subramaniam, S. Sahu, N. Rao","doi":"10.1093/MNRAS/STAA3758","DOIUrl":"https://doi.org/10.1093/MNRAS/STAA3758","url":null,"abstract":"We present the UV photometry of the globular cluster NGC 1261 using images acquired with the Ultraviolet Imaging Telescope (UVIT) on-board ASTROSAT. We performed PSF photometry on four near-UV (NUV) and two far-UV (FUV) images and constructed UV colour-magnitude diagrams (CMDs), in combination with HST, Gaia, and ground-based optical photometry for member stars. We detected the full horizontal branch (HB) in NUV, blue HB in the FUV and identified two extreme HB (EHB) stars. HB stars have a tight sequence in UV-optical CMDs well-fitted with isochrones generated (12.6 Gyr age, [Fe/H] = -1.27 metallicity) using updated BaSTI-IAC models. Effective temperatures (Teff), luminosities and radii of bright HB stars were estimated using spectral energy distribution. As we detect the complete sample of UV bright HB stars, the hot end of the HB distribution is found to terminate at the G-jump (Teff ~ 11500 K). The two EHB stars, fitted well with single spectra, have Teff= 31,000 K and a mass = 0.495Msun and follow the same Teff-Radius relation of the blue HB stars. We constrain the formation pathways of these EHB stars to extreme mass loss in the RGB phase (either due to rotation or enhanced Helium), OR early hot-flash scenario.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77491547","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 : 2020-12-01DOI: 10.31577/CAOSP.2021.51.1.58
J. Korth, A. Moharana, M. Pešta, D. Czavalinga, K. Conroy
Eclipsing Binaries (EBs) are known to be the source of most accurate stellar parameters, which are important for testing theories of stellar evolution. With improved quality and quantity of observations using space telescopes like {it TESS}, there is an urgent need for accuracy in modeling to obtain precise parameters. We use the soon to be released texttt{PHOEBE 2.3} EB modeling package to test the robustness and accuracy of parameters and their dependency on choice of parameters for optimization.
{"title":"Consequences of parameterization choice on eclipsing binary light curve solutions","authors":"J. Korth, A. Moharana, M. Pešta, D. Czavalinga, K. Conroy","doi":"10.31577/CAOSP.2021.51.1.58","DOIUrl":"https://doi.org/10.31577/CAOSP.2021.51.1.58","url":null,"abstract":"Eclipsing Binaries (EBs) are known to be the source of most accurate stellar parameters, which are important for testing theories of stellar evolution. With improved quality and quantity of observations using space telescopes like {it TESS}, there is an urgent need for accuracy in modeling to obtain precise parameters. We use the soon to be released texttt{PHOEBE 2.3} EB modeling package to test the robustness and accuracy of parameters and their dependency on choice of parameters for optimization.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78783703","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 : 2020-12-01DOI: 10.52526/25792776-2020.67.2-251
I. Andronov, K. Andrych, L. Chinarova, D. Tvardovskyi
The software MAVKA is described, which was elaborated for statistically optimal determination of the characteristics of the extrema of 1000+ variable stars of different types, mainly eclipsing and pulsating. The approximations are phenomenological, but not physical. As often, the discovery of a new variable star is made on time series of a single-filter (single-channel) data, and there is no possibility to determine parameters needed for physical modelling (e.g. temperature, radial velocities, mass ratio of binaries). Besides classical polynomial approximation "AP" (we limited the degree of the polynomial from 2 to 9), there are realized symmetrical approximations (symmetrical polynomials "SP", "wall-supported" horizontal line "WSL" and parabola "WSP", restricted polynomials of non-integer order based on approximations of the functions proposed by Andronov (2012) and Mikulasek (2015) and generally asymmetric functions (asymptotic parabola "AP", parabolic spline "PS", generalized hyperbolic secant function "SECH" and "log-normal-like" "BSK"). This software is a successor of the "Observation Obscurer" with some features for the variable star research, including a block for "running parabola" "RP" scalegram and approximation. Whereas the RP is oriented on approximation of the complete data set. MAVKA is pointed to parts of the light curve close to extrema (including total eclipses and transits of stars and exoplanets). The functions for wider intervals, covering the eclipse totally, were discussed in 2017Ap.....60...57A . Global and local approximations are reviewed in 2020kdbd.book..191A . The software is available at this http URL and https://katerynaandrych.wixsite.com/mavka. We have analyzed the data from own observations, as well as from monitoring obtained at ground-based and space (currently, mainly, TESS) observatories. It may be used for signals of any nature.
{"title":"Astroinformatics: Statistically Optimal Approximations of Near-Extremal Parts with Application to Variable Stars","authors":"I. Andronov, K. Andrych, L. Chinarova, D. Tvardovskyi","doi":"10.52526/25792776-2020.67.2-251","DOIUrl":"https://doi.org/10.52526/25792776-2020.67.2-251","url":null,"abstract":"The software MAVKA is described, which was elaborated for statistically optimal determination of the characteristics of the extrema of 1000+ variable stars of different types, mainly eclipsing and pulsating. The approximations are phenomenological, but not physical. As often, the discovery of a new variable star is made on time series of a single-filter (single-channel) data, and there is no possibility to determine parameters needed for physical modelling (e.g. temperature, radial velocities, mass ratio of binaries). Besides classical polynomial approximation \"AP\" (we limited the degree of the polynomial from 2 to 9), there are realized symmetrical approximations (symmetrical polynomials \"SP\", \"wall-supported\" horizontal line \"WSL\" and parabola \"WSP\", restricted polynomials of non-integer order based on approximations of the functions proposed by Andronov (2012) and Mikulasek (2015) and generally asymmetric functions (asymptotic parabola \"AP\", parabolic spline \"PS\", generalized hyperbolic secant function \"SECH\" and \"log-normal-like\" \"BSK\"). This software is a successor of the \"Observation Obscurer\" with some features for the variable star research, including a block for \"running parabola\" \"RP\" scalegram and approximation. Whereas the RP is oriented on approximation of the complete data set. MAVKA is pointed to parts of the light curve close to extrema (including total eclipses and transits of stars and exoplanets). The functions for wider intervals, covering the eclipse totally, were discussed in 2017Ap.....60...57A . Global and local approximations are reviewed in 2020kdbd.book..191A . The software is available at this http URL and https://katerynaandrych.wixsite.com/mavka. We have analyzed the data from own observations, as well as from monitoring obtained at ground-based and space (currently, mainly, TESS) observatories. It may be used for signals of any nature.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81484638","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}
Results of evolutionary modelling of subdwarf B stars are presented. For the first time, we explore the core and near-core mixing in the subdwarf B stars using new algorithms available in the MESA code: the predictive mixing scheme and the convective premixing scheme. We show how both methods handle the problems with determination of convective boundary, discrepancy between core masses obtained from asteroseismology and evolutionary models, and long-standing problems related to the core-helium-burning phase such as splitting of the convective core and the occurrence of breathing pulses. We find that the convective premixing scheme is the preferable algorithm. The masses of the convective core in case of the predictive mixing and the combined convective and semiconvective regions in case of the convective premixing scheme are higher than in the models with only the Ledoux criterion, but they are still lower than the seismic-derived values. Both algorithms are promising and alternative methods of studying models of subdwarf B stars.
{"title":"Evolutionary modelling of subdwarf B stars using mesa with the predictive mixing and convective pre-mixing schemes","authors":"J. Ostrowski, A. Baran, S. Sanjayan, S. K. Sahoo","doi":"10.1093/MNRAS/STAA3751","DOIUrl":"https://doi.org/10.1093/MNRAS/STAA3751","url":null,"abstract":"Results of evolutionary modelling of subdwarf B stars are presented. For the first time, we explore the core and near-core mixing in the subdwarf B stars using new algorithms available in the MESA code: the predictive mixing scheme and the convective premixing scheme. We show how both methods handle the problems with determination of convective boundary, discrepancy between core masses obtained from asteroseismology and evolutionary models, and long-standing problems related to the core-helium-burning phase such as splitting of the convective core and the occurrence of breathing pulses. We find that the convective premixing scheme is the preferable algorithm. The masses of the convective core in case of the predictive mixing and the combined convective and semiconvective regions in case of the convective premixing scheme are higher than in the models with only the Ledoux criterion, but they are still lower than the seismic-derived values. Both algorithms are promising and alternative methods of studying models of subdwarf B stars.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78446614","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}
M. M. Nyamai, L. Chomiuk, V. Ribeiro, P. Woudt, J. Strader, K. Sokolovsky, K. Sokolovsky
V445 Puppis is the only helium nova observed to date; its eruption in late 2000 showed high velocities up to 8500 km/s and a remarkable bipolar morphology cinched by an equatorial dust disc. Here we present multi-frequency radio observations of V445 Pup obtained with the Very Large Array (VLA) spanning 1.5 to 43.3 GHz, and between 2001 January and 2008 March (days 89 to 2700 after eruption). The radio light curve is dominated by synchrotron emission over these seven years, and shows four distinct radio flares. Resolved radio images obtained in the VLA A configuration show that the synchrotron emission hugs the equatorial disc, and comparisons to near-IR images of the nova clearly demonstrate that it is the densest ejecta, not the fastest ejecta, that are the sites of the synchrotron emission in V445 Pup. The data are consistent with a model where the synchrotron emission is produced by a wind from the white dwarf impacting the dense equatorial disc, resulting in shocks and particle acceleration. The individual synchrotron flares may be associated with density enhancements in the equatorial disc and/ or velocity variations in the wind from the white dwarf. This overall scenario is similar to a common picture of shock production in hydrogen-rich classical novae, but V445 Pup is remarkable in that these shocks persist for almost a decade, much longer than the weeks or months for which shocks are typically observed in classical novae.
{"title":"Radio light curves and imaging of the helium nova V445 Puppis reveal seven years of synchrotron emission","authors":"M. M. Nyamai, L. Chomiuk, V. Ribeiro, P. Woudt, J. Strader, K. Sokolovsky, K. Sokolovsky","doi":"10.1093/mnras/staa3712","DOIUrl":"https://doi.org/10.1093/mnras/staa3712","url":null,"abstract":"V445 Puppis is the only helium nova observed to date; its eruption in late 2000 showed high velocities up to 8500 km/s and a remarkable bipolar morphology cinched by an equatorial dust disc. Here we present multi-frequency radio observations of V445 Pup obtained with the Very Large Array (VLA) spanning 1.5 to 43.3 GHz, and between 2001 January and 2008 March (days 89 to 2700 after eruption). The radio light curve is dominated by synchrotron emission over these seven years, and shows four distinct radio flares. Resolved radio images obtained in the VLA A configuration show that the synchrotron emission hugs the equatorial disc, and comparisons to near-IR images of the nova clearly demonstrate that it is the densest ejecta, not the fastest ejecta, that are the sites of the synchrotron emission in V445 Pup. The data are consistent with a model where the synchrotron emission is produced by a wind from the white dwarf impacting the dense equatorial disc, resulting in shocks and particle acceleration. The individual synchrotron flares may be associated with density enhancements in the equatorial disc and/ or velocity variations in the wind from the white dwarf. This overall scenario is similar to a common picture of shock production in hydrogen-rich classical novae, but V445 Pup is remarkable in that these shocks persist for almost a decade, much longer than the weeks or months for which shocks are typically observed in classical novae.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74618183","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}
Hot stars are the main source of ionization of the interstellar medium and its enrichment due to heavy elements. Constraining the physical conditions of their environments is crucial to understand how these stars evolve and their impact on the evolution of galaxies. Spectroscopy allows to access the physics, the chemistry, and the dynamics of these objects, but not the spatial distribution of these objects. Only long-baseline interferometry can resolve photospheres and close environments, and, combining spectroscopy and interferometry, spectro-interferometry allows to draw an even more detailed picture of hot stars. The objective of my thesis was to investigate the physical properties of the photosphere and circumstellar environment of massive hot stars confronting multi-band spectroscopic or spectro-interferometric observations and sophisticated non-LTE radiative transfer codes. My work was focused on two main lines of research. The first concerns radiative line-driven winds. Using UV and visible spectroscopic data and the radiative transfer code CMFGEN, I investigated the weak wind phenomenon on a sample of nine Galactic O stars. This study shows for the first time that the weak wind phenomenon, originally found for O dwarfs, also exists on more evolved O stars and that future studies must evaluate its impact on the evolution of massive stars. My other line of research concerns the study of classical Be stars, the fastest rotators among the non-degenerated stars, and which are surrounded by rotating equatorial disks. I studied the Be star o Aquarii using Hα (CHARA/VEGA) and Brγ (VLTI/AMBER) spectro-interferometric observations, the radiative transfer code HDUST, and developing new automatic procedures to better constrain the kinematics of the disk. This multi-band study allowed to draw the most detailed picture of this object and its environment, to test the limits of the current generation of radiative transfer models, and paved the way to my future work on a large samples of Be stars observed with VEGA, AMBER, and the newly available VLTI mid-infrared combiner MATISSE.
{"title":"Disks and winds around hot stars: new insights from multi-wavelength spectroscopy and interferometry","authors":"E. S. G. D. Almeida","doi":"10.5281/ZENODO.4659014","DOIUrl":"https://doi.org/10.5281/ZENODO.4659014","url":null,"abstract":"Hot stars are the main source of ionization of the interstellar medium and its enrichment due to heavy elements. Constraining the physical conditions of their environments is crucial to understand how these stars evolve and their impact on the evolution of galaxies. \u0000Spectroscopy allows to access the physics, the chemistry, and the dynamics of these objects, but not the spatial distribution of these objects. Only long-baseline interferometry can resolve photospheres and close environments, and, combining spectroscopy and interferometry, spectro-interferometry allows to draw an even more detailed picture of hot stars. \u0000The objective of my thesis was to investigate the physical properties of the photosphere and circumstellar environment of massive hot stars confronting multi-band spectroscopic or spectro-interferometric observations and sophisticated non-LTE radiative transfer codes. \u0000My work was focused on two main lines of research. The first concerns radiative line-driven winds. Using UV and visible spectroscopic data and the radiative transfer code CMFGEN, I investigated the weak wind phenomenon on a sample of nine Galactic O stars. This study shows for the first time that the weak wind phenomenon, originally found for O dwarfs, also exists on more evolved O stars and that future studies must evaluate its impact on the evolution of massive stars. \u0000My other line of research concerns the study of classical Be stars, the fastest rotators among the non-degenerated stars, and which are surrounded by rotating equatorial disks. I studied the Be star o Aquarii using Hα (CHARA/VEGA) and Brγ (VLTI/AMBER) spectro-interferometric observations, the radiative transfer code HDUST, and developing new automatic procedures to better constrain the kinematics of the disk. This multi-band study allowed to draw the most detailed picture of this object and its environment, to test the limits of the current generation of radiative transfer models, and paved the way to my future work on a large samples of Be stars observed with VEGA, AMBER, and the newly available VLTI mid-infrared combiner MATISSE.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84080797","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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