Samrat Ghosh, S. Mondal, S. Dutta, R. Das, S. Joshi, S. Lata, Dhrimadri Khata, A. Panja
We present here optical I-band photometric variability study down to $simeq$ 19 mag of a young ($sim$2-3 Myr) star-forming region IC 348 in the Perseus molecular cloud. We aim to explore the fast rotation (in the time-scales of hours) in Very Low Mass stars (VLMs) including Brown Dwarfs (BDs). From a sample of 177 light-curves using our new I-band observations, we detect new photometric variability in 22 young M-dwarfs including 6 BDs, which are bonafide members in IC 348 and well-characterized in the spectral type of M-dwarfs. Out of 22 variables, 11 M dwarfs including one BD show hour-scale periodic variability in the period range 3.5 - 11 hours and rest are aperiodic in nature. Interestingly, an optical flare is detected in a young M2.75 dwarf in one night data on 20 December 2016. From the flare light curve, we estimate the emitted flared energy of 1.48 $times$ 10$^{35}$ ergs. The observed flared energy with an uncertainty of tens of per cent is close to the super-flare range ($sim$ 10$^{34}$ ergs), which is rarely observed in active M dwarfs.
{"title":"Fast photometric variability of very low mass stars in IC 348: detection of superflare in an M dwarf","authors":"Samrat Ghosh, S. Mondal, S. Dutta, R. Das, S. Joshi, S. Lata, Dhrimadri Khata, A. Panja","doi":"10.1093/mnras/staa3574","DOIUrl":"https://doi.org/10.1093/mnras/staa3574","url":null,"abstract":"We present here optical I-band photometric variability study down to $simeq$ 19 mag of a young ($sim$2-3 Myr) star-forming region IC 348 in the Perseus molecular cloud. We aim to explore the fast rotation (in the time-scales of hours) in Very Low Mass stars (VLMs) including Brown Dwarfs (BDs). From a sample of 177 light-curves using our new I-band observations, we detect new photometric variability in 22 young M-dwarfs including 6 BDs, which are bonafide members in IC 348 and well-characterized in the spectral type of M-dwarfs. Out of 22 variables, 11 M dwarfs including one BD show hour-scale periodic variability in the period range 3.5 - 11 hours and rest are aperiodic in nature. Interestingly, an optical flare is detected in a young M2.75 dwarf in one night data on 20 December 2016. From the flare light curve, we estimate the emitted flared energy of 1.48 $times$ 10$^{35}$ ergs. The observed flared energy with an uncertainty of tens of per cent is close to the super-flare range ($sim$ 10$^{34}$ ergs), which is rarely observed in active M dwarfs.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80238477","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. Marconi, R. Molinaro, V. Ripepi, S. Leccia, I. Musella, G. De Somma, M. Gatto, M. Moretti
On the basis of an extended set of nonlinear convective RR Lyrae pulsation models we derive the first theoretical light curves in the Gaia bands and the corresponding intensity-weighted mean magnitudes and pulsation amplitudes. The effects of chemical com-position on the derived Bailey diagrams in the Gaia filters are discussed for both Fundamental and First Overtone mode pulsators. The inferred mean magnitudes and colors are used to derive the first theoretical Period-Wesenheit relations for RR Lyrae in the Gaia filters. The application of the theoretical Period-Wesenheit relations for both the Fundamental and FirstOvertone mode to Galactic RR Lyrae in the Gaia Data Release 2 database and complementary information on individual metal abundances, allows us to derive theoretical estimates of their individual parallaxes. These results are compared with the astrometric solutions to conclude that a very small offset, consistent with zero, is required in order to reconcile the predicted distances with Gaia results.
{"title":"A theoretical scenario for Galactic RR Lyrae in the Gaia data base: constraints on the parallax offset","authors":"M. Marconi, R. Molinaro, V. Ripepi, S. Leccia, I. Musella, G. De Somma, M. Gatto, M. Moretti","doi":"10.1093/mnras/staa3558","DOIUrl":"https://doi.org/10.1093/mnras/staa3558","url":null,"abstract":"On the basis of an extended set of nonlinear convective RR Lyrae pulsation models we derive the first theoretical light curves in the Gaia bands and the corresponding intensity-weighted mean magnitudes and pulsation amplitudes. The effects of chemical com-position on the derived Bailey diagrams in the Gaia filters are discussed for both Fundamental and First Overtone mode pulsators. The inferred mean magnitudes and colors are used to derive the first theoretical Period-Wesenheit relations for RR Lyrae in the Gaia filters. The application of the theoretical Period-Wesenheit relations for both the Fundamental and FirstOvertone mode to Galactic RR Lyrae in the Gaia Data Release 2 database and complementary information on individual metal abundances, allows us to derive theoretical estimates of their individual parallaxes. These results are compared with the astrometric solutions to conclude that a very small offset, consistent with zero, is required in order to reconcile the predicted distances with Gaia results.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87085513","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 : 2020-11-10DOI: 10.1051/0004-6361/202039490
C. R. Braga, A. Vourlidas
Context. We study two coronal mass ejections (CMEs) observed between April 1-2, 2019 by both the inner Wide-Field Imager for Parker Solar Probe (WISPR-I) and the inner heliospheric imager (HI-1) on board STEREO-A. This is the first study of CME observations from two viewpoints in similar directions but at considerably different solar distances. Aims. Our objective is to understand how the PSP observations affect the CME kinematics, especially due to its proximity to the Sun. Methods. We estimate the CME positions, speeds, accelerations, propagation directions and longitudinal deflections using imaging observations from two spacecraft, and a set of analytical expressions that consider the CME as a point structure and take into account the rapid change in spacecraft position. Results. We find that both CMEs are slow ($< 400 km s^{-1}$), propagating eastward of the Sun-Earth line. The second CME seems to accelerate between $sim 0.1$ to $sim 0.2 au$ and deflect westward with an angular speed consistent with the solar rotation speed. We find some discrepancies in the CME solar distance (up to $0.05 au$, particularly for CME #1), latitude (up to $sim10^{circ}$) and longitude (up to $24^{circ}$) when comparing results from different fit cases (different observations or set of free parameters). Conclusions. Discrepancies in longitude are likely due to the feature tracked visually rather than instrumental biases or fit assumptions. For similar reasons, the CME #1 solar distance, as derived from WISPR-I observations, is larger than the HI-1 result, regardless of the fit parameters considered. Error estimates for CME kinematics do not show any clear trend associated to the observing instrument. The source region location and the lack of any clear in situ counterparts (both at near-Earth and at PSP) support our estimate of the propagation direction for both events.
{"title":"Coronal mass ejections observed by heliospheric imagers at 0.2 and 1 au","authors":"C. R. Braga, A. Vourlidas","doi":"10.1051/0004-6361/202039490","DOIUrl":"https://doi.org/10.1051/0004-6361/202039490","url":null,"abstract":"Context. We study two coronal mass ejections (CMEs) observed between April 1-2, 2019 by both the inner Wide-Field Imager for Parker Solar Probe (WISPR-I) and the inner heliospheric imager (HI-1) on board STEREO-A. This is the first study of CME observations from two viewpoints in similar directions but at considerably different solar distances. Aims. Our objective is to understand how the PSP observations affect the CME kinematics, especially due to its proximity to the Sun. Methods. We estimate the CME positions, speeds, accelerations, propagation directions and longitudinal deflections using imaging observations from two spacecraft, and a set of analytical expressions that consider the CME as a point structure and take into account the rapid change in spacecraft position. Results. We find that both CMEs are slow ($< 400 km s^{-1}$), propagating eastward of the Sun-Earth line. The second CME seems to accelerate between $sim 0.1$ to $sim 0.2 au$ and deflect westward with an angular speed consistent with the solar rotation speed. We find some discrepancies in the CME solar distance (up to $0.05 au$, particularly for CME #1), latitude (up to $sim10^{circ}$) and longitude (up to $24^{circ}$) when comparing results from different fit cases (different observations or set of free parameters). Conclusions. Discrepancies in longitude are likely due to the feature tracked visually rather than instrumental biases or fit assumptions. For similar reasons, the CME #1 solar distance, as derived from WISPR-I observations, is larger than the HI-1 result, regardless of the fit parameters considered. Error estimates for CME kinematics do not show any clear trend associated to the observing instrument. The source region location and the lack of any clear in situ counterparts (both at near-Earth and at PSP) support our estimate of the propagation direction for both events.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82086455","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 : 2020-11-10DOI: 10.5194/EGUSPHERE-EGU21-282
L. Svalgaard
The long-standing disparity between the sunspot number record and the Hoyt and Schatten (1998, HS while a reconstruction of the group number with monthly resolution (with many more degrees of freedom) validate the size of Solar Cycle 11 given by the revised series that the dissenting series fail to meet.
{"title":"Several Populations of Sunspot Group Numbers – Resolving a Conundrum","authors":"L. Svalgaard","doi":"10.5194/EGUSPHERE-EGU21-282","DOIUrl":"https://doi.org/10.5194/EGUSPHERE-EGU21-282","url":null,"abstract":"The long-standing disparity between the sunspot number record and the Hoyt and Schatten (1998, HS while a reconstruction of the group number with monthly resolution (with many more degrees of freedom) validate the size of Solar Cycle 11 given by the revised series that the dissenting series fail to meet.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75480128","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 : 2020-10-31DOI: 10.32023/0001-5237/69.3.2
M. Siwak, M. Dr'o.zd.z, Karolina Gut, M. Winiarski, W. Ogłoza, G. Stachowski
Results of high-cadence multi-colour observations of 121 pre-main sequence stars available from the northern hemisphere are presented. The aim of this survey was to detect transit-like signatures caused by occultation of these young stars and their accretion-induced hot spots by close-in planets and/or dusty clumps. Although none planetary transits were detected, our data allow to determine rotational periods for some T Tauri stars, characterise accretion processes operating in classical T Tauri-type stars in time scales ranging from a few minutes to days, as well as the large-scale dips caused by dusty warped discs.
{"title":"Mount Suhora high cadence photometric survey of T Tauri-type stars","authors":"M. Siwak, M. Dr'o.zd.z, Karolina Gut, M. Winiarski, W. Ogłoza, G. Stachowski","doi":"10.32023/0001-5237/69.3.2","DOIUrl":"https://doi.org/10.32023/0001-5237/69.3.2","url":null,"abstract":"Results of high-cadence multi-colour observations of 121 pre-main sequence stars available from the northern hemisphere are presented. The aim of this survey was to detect transit-like signatures caused by occultation of these young stars and their accretion-induced hot spots by close-in planets and/or dusty clumps. Although none planetary transits were detected, our data allow to determine rotational periods for some T Tauri stars, characterise accretion processes operating in classical T Tauri-type stars in time scales ranging from a few minutes to days, as well as the large-scale dips caused by dusty warped discs.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91460504","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. Trabucchi, P. Wood, N. Mowlavi, G. Pastorelli, P. Marigo, L. Girardi, T. Lebzelter
Long-period variability in luminous red giants has several promising applications, all of which require models able to accurately predict pulsation periods. Linear pulsation models have proven successful in reproducing the observed periods of overtone modes in evolved red giants, but they fail to accurately predict their fundamental mode periods. Here, we use a 1D hydrodynamic code to investigate the long-period variability of M-type asymptotic giant branch stars in the nonlinear regime. We examine the period and stability of low-order radial pulsation modes as a function of mass and radius, and find overtone mode periods in complete agreement with predictions from linear pulsation models. In contrast, nonlinear models predict an earlier onset of dominant fundamental mode pulsation, and shorter periods at large radii. Both features lead to a substantially better agreement with observations, that we verify against OGLE and Gaia data for the Magellanic Clouds. We provide simple analytic relations describing the nonlinear fundamental mode period-mass-radius relation. Differences with respect to linear predictions originate from the readjustment of the envelope structure induced by large-amplitude pulsation. We investigate the impact of turbulent viscosity on linear and nonlinear pulsation, and probe possible effects of varying metallicity and carbon abundance.
{"title":"Modelling long-period variables – II. Fundamental mode pulsation in the non-linear regime","authors":"M. Trabucchi, P. Wood, N. Mowlavi, G. Pastorelli, P. Marigo, L. Girardi, T. Lebzelter","doi":"10.1093/mnras/staa3356","DOIUrl":"https://doi.org/10.1093/mnras/staa3356","url":null,"abstract":"Long-period variability in luminous red giants has several promising applications, all of which require models able to accurately predict pulsation periods. Linear pulsation models have proven successful in reproducing the observed periods of overtone modes in evolved red giants, but they fail to accurately predict their fundamental mode periods. Here, we use a 1D hydrodynamic code to investigate the long-period variability of M-type asymptotic giant branch stars in the nonlinear regime. We examine the period and stability of low-order radial pulsation modes as a function of mass and radius, and find overtone mode periods in complete agreement with predictions from linear pulsation models. In contrast, nonlinear models predict an earlier onset of dominant fundamental mode pulsation, and shorter periods at large radii. Both features lead to a substantially better agreement with observations, that we verify against OGLE and Gaia data for the Magellanic Clouds. We provide simple analytic relations describing the nonlinear fundamental mode period-mass-radius relation. Differences with respect to linear predictions originate from the readjustment of the envelope structure induced by large-amplitude pulsation. We investigate the impact of turbulent viscosity on linear and nonlinear pulsation, and probe possible effects of varying metallicity and carbon abundance.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76108436","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 : 2020-10-26DOI: 10.1051/0004-6361/202039912
G. Rüdiger, M. Küker
In order to explain the modulation of the solar rotation law during the activity minima and maxima the angular momentum transport by rotating magnetoconvection is numerically simulated when a convective box is penetrated by an inclined azimuthal magnetic field. Turbulence-induced kinetic and magnetic stresses {em and} the Maxwell stress of the large-scale magnetic background field are the basic transporters. Without rotation the sign of the total stress naturally depends on the signs of the field components as positive (negative) $B_theta B_phi$ transport the angular momentum poleward (equatorward). For fast enough rotation, however, the turbulence-originated $Lambda$ effect starts to dominate the transport of the angular momentum. The simulations show that positive angles between the azimuthal field and the two meridional magnetic field components (as expected to be realized by induction of solar-type rotation laws) reduce the inward radial as well as the equatorward latitudinal transport by the rotating magnetoconvection. In accordance with the observations the magnetically influenced rotation law at the solar surface proves to be flatter than the nonmagnetic one even displaying a slightly decelerated equator .
{"title":"Angular momentum transport from magnetoconvection and the magnetic modulation of the solar differential rotation","authors":"G. Rüdiger, M. Küker","doi":"10.1051/0004-6361/202039912","DOIUrl":"https://doi.org/10.1051/0004-6361/202039912","url":null,"abstract":"In order to explain the modulation of the solar rotation law during the activity minima and maxima the angular momentum transport by rotating magnetoconvection is numerically simulated when a convective box is penetrated by an inclined azimuthal magnetic field. Turbulence-induced kinetic and magnetic stresses {em and} the Maxwell stress of the large-scale magnetic background field are the basic transporters. Without rotation the sign of the total stress naturally depends on the signs of the field components as positive (negative) $B_theta B_phi$ transport the angular momentum poleward (equatorward). For fast enough rotation, however, the turbulence-originated $Lambda$ effect starts to dominate the transport of the angular momentum. The simulations show that positive angles between the azimuthal field and the two meridional magnetic field components (as expected to be realized by induction of solar-type rotation laws) reduce the inward radial as well as the equatorward latitudinal transport by the rotating magnetoconvection. In accordance with the observations the magnetically influenced rotation law at the solar surface proves to be flatter than the nonmagnetic one even displaying a slightly decelerated equator .","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80176546","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}
The Oef category gathers rapidly rotating and evolved O-stars displaying a centrally reversed He II 4686 emission line. The origin of the variability of their photospheric and wind spectral lines is debated, with rotational modulation or pulsations as the main contenders. To shed new light on this question, we analysed high-quality and high-cadence TESS photometric time series for five Oef stars. We also collected a new time series of spectra for one target (lambda Cep) which had been the subject of specific debates in the last years. These observations reveal the variety of Oef behaviours. While space-based photometric data reveal substantial red noise components in all targets, only zeta Pup seems to display a long-lived periodicity. In our sample, stars exhibit a dominant signal at low frequencies but it appears relatively short-lived. This is reminiscent of rotational modulations by transient photospheric spots, though this scenario is challenged by the case of HD 14442, whose 1.230 d$^{-1}$ signal significantly exceeds the critical rotational frequency. In parallel, no evidence of persistent p-mode non-radial pulsations is found in either photometry or spectroscopy of the stars, only temporary excitation of g-mode pulsations could offer an alternative explanation for the dominant signals. Finally, the revised luminosities of the stars using GAIA-DR2 show that they are not all supergiants as zeta Pup. The question then arises whether the Oef peculiarity denotes a homogeneous class of objects after all.
Oef类聚集了快速旋转和演化的o型恒星，显示出中央反转的He II 4686发射线。它们的光球和风谱线变化的起源是有争议的，旋转调制或脉动是主要的竞争者。为了阐明这个问题，我们分析了5颗Oef恒星的高质量和高节奏的TESS光度时间序列。我们还收集了一个目标(lambda Cep)的新的时间序列光谱，该目标在过去几年中一直是具体争论的主题。这些观察结果揭示了Oef行为的多样性。虽然基于空间的光度数据显示所有目标中都有大量的红噪声成分，但只有zeta Pup似乎显示出长期的周期性。在我们的样本中，恒星表现出低频的主导信号，但它似乎相对较短。这让人想起瞬态光球点的旋转调制，尽管这种情况受到HD 14442的挑战，其1.230 d$^{-1}$信号明显超过临界旋转频率。与此同时，在恒星的光度学或光谱学中都没有发现持续的p模式非径向脉动的证据，只有g模式脉动的暂时激发可以为主导信号提供另一种解释。最后，使用GAIA-DR2修正的恒星亮度表明，它们并不都是像zeta Pup那样的超巨星。那么问题来了，Oef的特性是否代表了一个同质的对象。
{"title":"Similar but different: the varied landscape of Onfp/Oef stars variability","authors":"G. Rauw, Y. Nazé","doi":"10.1093/mnras/staa3310","DOIUrl":"https://doi.org/10.1093/mnras/staa3310","url":null,"abstract":"The Oef category gathers rapidly rotating and evolved O-stars displaying a centrally reversed He II 4686 emission line. The origin of the variability of their photospheric and wind spectral lines is debated, with rotational modulation or pulsations as the main contenders. To shed new light on this question, we analysed high-quality and high-cadence TESS photometric time series for five Oef stars. We also collected a new time series of spectra for one target (lambda Cep) which had been the subject of specific debates in the last years. These observations reveal the variety of Oef behaviours. While space-based photometric data reveal substantial red noise components in all targets, only zeta Pup seems to display a long-lived periodicity. In our sample, stars exhibit a dominant signal at low frequencies but it appears relatively short-lived. This is reminiscent of rotational modulations by transient photospheric spots, though this scenario is challenged by the case of HD 14442, whose 1.230 d$^{-1}$ signal significantly exceeds the critical rotational frequency. In parallel, no evidence of persistent p-mode non-radial pulsations is found in either photometry or spectroscopy of the stars, only temporary excitation of g-mode pulsations could offer an alternative explanation for the dominant signals. Finally, the revised luminosities of the stars using GAIA-DR2 show that they are not all supergiants as zeta Pup. The question then arises whether the Oef peculiarity denotes a homogeneous class of objects after all.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89280134","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 : 2020-10-21DOI: 10.1051/0004-6361/201935538
D. Reese, G. Mirouh, F. Lara, M. Rieutord, B. Putigny
Recent numerical and theoretical considerations have shown that low-degree acoustic modes in rapidly rotating stars follow an asymptotic formula and recent observations of pulsations in rapidly rotating delta Scuti stars seem to match these expectations. However, a key question is whether strong gradients or discontinuities can adversely affect this pattern to the point of hindering its identification. Other important questions are how rotational splittings are affected by the 2D rotation profiles expected from baroclinic effects and whether it is possible to probe the rotation profile using these splittings. Accordingly, we numerically calculate pulsation modes in continuous and discontinuous rapidly rotating models produced by the 2D ESTER (Evolution STEllaire en Rotation) code. This spectral multi-domain code self-consistently calculates the rotation profile based on baroclinic effects and allows us to introduce discontinuities without loss of numerical accuracy. Pulsations are calculated using an adiabatic version of the Two-dimensional Oscillation Program (TOP) code. The variational principle is used to confirm the high accuracy of the pulsation frequencies and to derive an integral formula that closely matches the generalised rotational splittings, except when modes are involved in avoided crossings. This potentially allows us to probe the the rotation profile using inverse theory. Acoustic glitch theory, applied along the island mode orbit deduced from ray dynamics, can correctly predict the periodicity of the glitch frequency pattern produced by a discontinuity or the Gamma1 dip related to the He II ionisation zone in some of the models. The asymptotic frequency pattern remains sufficiently well preserved to potentially allow its detection in observed stars.
最近的数值和理论研究表明，快速旋转恒星中的低度声学模式遵循渐近公式，最近对快速旋转的三角星的脉动观测似乎符合这些期望。然而，一个关键的问题是，强梯度或不连续性是否会对这种模式产生不利影响，从而阻碍其识别。其他重要的问题是，斜压效应预期的二维旋转剖面如何影响旋转劈裂，以及是否有可能利用这些劈裂探测旋转剖面。因此，我们数值计算了由2D ESTER (Evolution STEllaire en Rotation)代码产生的连续和不连续快速旋转模型的脉动模式。该谱多域代码自一致地计算基于斜压效应的旋转剖面，并允许我们在不损失数值精度的情况下引入不连续。使用二维振荡程序(TOP)代码的绝热版本计算脉动。变分原理用于确认脉动频率的高精度，并推导出与广义旋转分裂密切匹配的积分公式，除非模态涉及避免交叉。这有可能使我们利用逆理论来探测旋转轮廓。声学故障理论，应用于从射线动力学推导出的岛模轨道，可以正确地预测由一些模型中与He II电离区相关的不连续或Gamma1 dip产生的故障频率模式的周期性。渐近频率模式保存得很好，有可能在被观测的恒星中被探测到。
{"title":"Oscillations of 2D ESTER models","authors":"D. Reese, G. Mirouh, F. Lara, M. Rieutord, B. Putigny","doi":"10.1051/0004-6361/201935538","DOIUrl":"https://doi.org/10.1051/0004-6361/201935538","url":null,"abstract":"Recent numerical and theoretical considerations have shown that low-degree acoustic modes in rapidly rotating stars follow an asymptotic formula and recent observations of pulsations in rapidly rotating delta Scuti stars seem to match these expectations. However, a key question is whether strong gradients or discontinuities can adversely affect this pattern to the point of hindering its identification. Other important questions are how rotational splittings are affected by the 2D rotation profiles expected from baroclinic effects and whether it is possible to probe the rotation profile using these splittings. Accordingly, we numerically calculate pulsation modes in continuous and discontinuous rapidly rotating models produced by the 2D ESTER (Evolution STEllaire en Rotation) code. This spectral multi-domain code self-consistently calculates the rotation profile based on baroclinic effects and allows us to introduce discontinuities without loss of numerical accuracy. Pulsations are calculated using an adiabatic version of the Two-dimensional Oscillation Program (TOP) code. The variational principle is used to confirm the high accuracy of the pulsation frequencies and to derive an integral formula that closely matches the generalised rotational splittings, except when modes are involved in avoided crossings. This potentially allows us to probe the the rotation profile using inverse theory. Acoustic glitch theory, applied along the island mode orbit deduced from ray dynamics, can correctly predict the periodicity of the glitch frequency pattern produced by a discontinuity or the Gamma1 dip related to the He II ionisation zone in some of the models. The asymptotic frequency pattern remains sufficiently well preserved to potentially allow its detection in observed stars.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77120207","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}
P. Denissenkov, C. Ruiz, S. Upadhyayula, F. Herwig
Recent spectroscopic measurements of the equivalent widths of the resonant Be II doublet and Ca II K lines and their ratios in expanding nova ejecta indicate surprisingly high abundances of $^7$Be with a typical mass fraction $X_mathrm{obs}(^7mathrm{Be}) = 10^{-4}$. This is an order of magnitude larger than theoretically predicted values of $X_mathrm{theor}(^7mathrm{Be})sim 10^{-5}$ for novae. We propose how this discrepancy can be reduced. We use an analytical solution of the $^7$Be production equations to demonstrate that $X_mathrm{theor}(^7mathrm{Be})$ is proportional to the $^4$He mass fraction $Y$ in the nova accreted envelope and then we perform computations of 1D hydrostatic evolution of the $1.15,M_odot$ CO nova model that confirm our conclusion based on the analytical solution. Our assumption of enhanced $^4$He abundances that helps to reduce the discrepancy between $X_mathrm{obs}(^7mathrm{Be})$ and $X_mathrm{theor}(^7mathrm{Be})$ is supported by UV, optical and IR spectroscopy data that reveal unusually high values of $Y$ in nova ejecta. We also show that a significantly increased abundance of $^3$He in nova accreted envelopes does not lead to higher values of $X_mathrm{theor}(^7mathrm{Be})$ because this assumption affects the evolution of nova models resulting in a decrease of both their peak temperatures and accreted masses and, as a consequence, in a reduced production of $^7$Be.
{"title":"An evidence-based assumption that helps to reduce the discrepancy between the observed and predicted 7Be abundances in novae","authors":"P. Denissenkov, C. Ruiz, S. Upadhyayula, F. Herwig","doi":"10.1093/mnrasl/slaa190","DOIUrl":"https://doi.org/10.1093/mnrasl/slaa190","url":null,"abstract":"Recent spectroscopic measurements of the equivalent widths of the resonant Be II doublet and Ca II K lines and their ratios in expanding nova ejecta indicate surprisingly high abundances of $^7$Be with a typical mass fraction $X_mathrm{obs}(^7mathrm{Be}) = 10^{-4}$. This is an order of magnitude larger than theoretically predicted values of $X_mathrm{theor}(^7mathrm{Be})sim 10^{-5}$ for novae. We propose how this discrepancy can be reduced. We use an analytical solution of the $^7$Be production equations to demonstrate that $X_mathrm{theor}(^7mathrm{Be})$ is proportional to the $^4$He mass fraction $Y$ in the nova accreted envelope and then we perform computations of 1D hydrostatic evolution of the $1.15,M_odot$ CO nova model that confirm our conclusion based on the analytical solution. Our assumption of enhanced $^4$He abundances that helps to reduce the discrepancy between $X_mathrm{obs}(^7mathrm{Be})$ and $X_mathrm{theor}(^7mathrm{Be})$ is supported by UV, optical and IR spectroscopy data that reveal unusually high values of $Y$ in nova ejecta. We also show that a significantly increased abundance of $^3$He in nova accreted envelopes does not lead to higher values of $X_mathrm{theor}(^7mathrm{Be})$ because this assumption affects the evolution of nova models resulting in a decrease of both their peak temperatures and accreted masses and, as a consequence, in a reduced production of $^7$Be.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88043924","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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