J. Hu, J. Webb, T. Ayres, M. Bainbridge, J. Barrow, M. Barstow, J. Berengut, R. Carswell, V. Dumont, V. Dzuba, V. Flambaum, C. C. Lee, N. Reindl, S. Preval, W. L. Tchang-Brillet
The gravitational potential phi = GM/Rc^2 at the surface of the white dwarf G191-B2B is 10,000 times stronger than that at the Earth's surface. Numerous photospheric absorption features are detected, making this a suitable environment to test theories in which the fundamental constants depend on gravity. We have measured the fine structure constant, alpha, at the white dwarf surface, used a newly calibrated Hubble Space Telescope STIS spectrum of G191-B2B, two new independent sets of laboratory Fe V wavelengths, and new atomic calculations of the sensitivity parameters that quantify Fe V wavelength dependency on alpha. The two results obtained are: dalpha/alpha = 6.36 +/- [0.33(stat) + 1.94(sys)] X 10^{-5} and dalpha/alpha = 4.21 +/- [0.47(stat) + 2.35(sys)] X 10^{-5}. The measurements hint that the fine structure constant increases slightly in the presence of strong gravitational fields. A comprehensive search for systematic errors is summarised, including possible effects from line misidentifications, line blending, stratification of the white dwarf atmosphere, the quadratic Zeeman effect and electric field effects, photospheric velocity flows, long-range wavelength distortions in the HST spectrum, and variations in the relative Fe isotopic abundances. None fully account for the observed deviation but the systematic uncertainties are heavily dominated by laboratory wavelength measurement precision.
{"title":"Measuring the fine structure constant on a white dwarf surface; a detailed analysis of Fe V absorption in G191-B2B","authors":"J. Hu, J. Webb, T. Ayres, M. Bainbridge, J. Barrow, M. Barstow, J. Berengut, R. Carswell, V. Dumont, V. Dzuba, V. Flambaum, C. C. Lee, N. Reindl, S. Preval, W. L. Tchang-Brillet","doi":"10.1093/mnras/staa3066","DOIUrl":"https://doi.org/10.1093/mnras/staa3066","url":null,"abstract":"The gravitational potential phi = GM/Rc^2 at the surface of the white dwarf G191-B2B is 10,000 times stronger than that at the Earth's surface. Numerous photospheric absorption features are detected, making this a suitable environment to test theories in which the fundamental constants depend on gravity. We have measured the fine structure constant, alpha, at the white dwarf surface, used a newly calibrated Hubble Space Telescope STIS spectrum of G191-B2B, two new independent sets of laboratory Fe V wavelengths, and new atomic calculations of the sensitivity parameters that quantify Fe V wavelength dependency on alpha. The two results obtained are: dalpha/alpha = 6.36 +/- [0.33(stat) + 1.94(sys)] X 10^{-5} and dalpha/alpha = 4.21 +/- [0.47(stat) + 2.35(sys)] X 10^{-5}. The measurements hint that the fine structure constant increases slightly in the presence of strong gravitational fields. A comprehensive search for systematic errors is summarised, including possible effects from line misidentifications, line blending, stratification of the white dwarf atmosphere, the quadratic Zeeman effect and electric field effects, photospheric velocity flows, long-range wavelength distortions in the HST spectrum, and variations in the relative Fe isotopic abundances. None fully account for the observed deviation but the systematic uncertainties are heavily dominated by laboratory wavelength measurement precision.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80784818","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}
Oscillations in the solar atmosphere have long been observed in quiet conditions, and increasingly also in data taken during solar flares. The chromosphere is known for its 3-minute signals, which are particularly strong over sunspot umbrae. These signals are thought to be driven by photospheric disturbances and their periods determined by the chromosphere's acoustic cut-off frequency. A small number of observations have shown the chromospheric 3-minute signals to be affected by energetic events such as solar flares, however the link between flare activity and these oscillatory signals remains unclear. In this work we present evidence of changes to the oscillatory structure of the chromosphere over a sunspot which occurs during the impulsive phase of an M1 flare. Using imaging data from the CRISP instrument across the H$alpha$ and Ca II 8542 {AA} spectral lines, we employed a method of fitting models to power spectra to produce maps of areas where there is evidence of oscillatory signals above a red noise background. Comparing results taken before and after the impulsive phase of the flare, we found that the oscillatory signals taken after the start of the flare differ in two ways: the locations of oscillatory signals had changed and the typical periods of the oscillations had tended to increase (in some cases increasing from $lt$100s to $sim$200s). Both of these results can be explained by a restructuring of the magnetic field in the chromosphere during the flare activity, which is backed up by images of coronal loops showing clear changes to magnetic connectivity. These results represent one of the many ways that active regions can be affected by solar flare events.
太阳大气的振荡长期以来一直是在安静的条件下观察到的，而且越来越多地出现在太阳耀斑期间的数据中。色球层以其3分钟信号而闻名，这种信号在太阳黑子本影上尤为强烈。这些信号被认为是由光球扰动驱动的，它们的周期由色球的声学截止频率决定。少量的观测表明，色球3分钟信号受到太阳耀斑等高能事件的影响，然而，耀斑活动与这些振荡信号之间的联系尚不清楚。在这项工作中，我们提出了在M1耀斑的脉冲阶段发生的太阳黑子上色球振荡结构变化的证据。利用CRISP仪器在H $alpha$和Ca II 8542 {AA}光谱线上的成像数据，我们采用了一种将模型拟合到功率谱的方法来生成在红噪声背景上有振荡信号证据的区域的地图。对比耀斑脉冲期前后的结果，我们发现耀斑开始后的振荡信号在两个方面有所不同:振荡信号的位置发生了变化，振荡的典型周期有增加的趋势(在某些情况下从$lt$ 100秒增加到$sim$ 200秒)。这两个结果都可以用耀斑活动期间色球层磁场的重构来解释，这一点得到日冕环图像的支持，日冕环显示了磁连通性的明显变化。这些结果代表了太阳耀斑事件影响活动区域的许多方式之一。
{"title":"The effect of a solar flare on chromospheric oscillations","authors":"D. Millar, L. Fletcher, R. Milligan","doi":"10.1093/MNRAS/STAB642","DOIUrl":"https://doi.org/10.1093/MNRAS/STAB642","url":null,"abstract":"Oscillations in the solar atmosphere have long been observed in quiet conditions, and increasingly also in data taken during solar flares. The chromosphere is known for its 3-minute signals, which are particularly strong over sunspot umbrae. These signals are thought to be driven by photospheric disturbances and their periods determined by the chromosphere's acoustic cut-off frequency. A small number of observations have shown the chromospheric 3-minute signals to be affected by energetic events such as solar flares, however the link between flare activity and these oscillatory signals remains unclear. In this work we present evidence of changes to the oscillatory structure of the chromosphere over a sunspot which occurs during the impulsive phase of an M1 flare. Using imaging data from the CRISP instrument across the H$alpha$ and Ca II 8542 {AA} spectral lines, we employed a method of fitting models to power spectra to produce maps of areas where there is evidence of oscillatory signals above a red noise background. Comparing results taken before and after the impulsive phase of the flare, we found that the oscillatory signals taken after the start of the flare differ in two ways: the locations of oscillatory signals had changed and the typical periods of the oscillations had tended to increase (in some cases increasing from $lt$100s to $sim$200s). Both of these results can be explained by a restructuring of the magnetic field in the chromosphere during the flare activity, which is backed up by images of coronal loops showing clear changes to magnetic connectivity. These results represent one of the many ways that active regions can be affected by solar flare events.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88648563","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}
We investigated the chromospheric activity of 60 pre-main-sequence (PMS) stars in four molecular clouds and five moving groups. It is considered that strong chromospheric activity is driven by the dynamo processes generated by the stellar rotation. In contrast, several researchers have pointed out that the chromospheres of PMS stars are activated by mass accretion from their protoplanetary disks. In this study, the Ca II infrared triplet (IRT) emission lines were investigated utilizing medium- and high-resolution spectroscopy. The observations were conducted with Nayuta/MALLS and Subaru/HDS. Additionally, archive data obtained by Keck/HIRES, VLT/UVES, and VLT/X-Shooter was used. The small ratios of the equivalent widths indicate that Ca II IRT emission lines arise primarily in dense chromospheric regions. Seven PMS stars show broad emission lines. Among them, four PMS stars have more than one order of magnitude brighter emission line fluxes compared to the low-mass stars in young open clusters. The four PMS stars have a high mass accretion rate, which indicates that the broad and strong emission results from a large mass accretion. However, most PMS stars exhibit narrow emission lines. No significant correlation was found between the accretion rate and flux of the emission line. The ratios of the surface flux of the Ca II IRT lines to the stellar bolometric luminosity, R'_IRT, of the PMS stars with narrow emission lines are as large as the largest R'_IRT of the low-mass stars in the young open clusters. This result indicates that most PMS stars, even in the classical T Tauri star stage, have chromospheric activity similar to zero-age main-sequence stars.
我们研究了4个分子云和5个运动群中的60颗前主序星(PMS)的色球活动。据认为，强烈的色球活动是由恒星旋转产生的发电机过程驱动的。相反，一些研究人员指出，PMS恒星的色球是由原行星盘的质量吸积激活的。本文利用中分辨率和高分辨率光谱研究了Ca II红外三重态(IRT)发射谱线。观察是用Nayuta/MALLS和Subaru/HDS进行的。此外，还使用了Keck/HIRES、VLT/UVES和VLT/X-Shooter获得的存档数据。较小的等效宽度比值表明，Ca II IRT发射线主要出现在密集的色球区。七颗PMS恒星显示出广泛的发射线。其中，4颗PMS恒星的发射谱线通量比年轻疏散星团中的低质量恒星亮一个数量级以上。这四颗PMS恒星的质量吸积率很高，这表明广泛而强烈的发射是大质量吸积的结果。然而，大多数PMS恒星显示出狭窄的发射线。在吸积速率和发射线的通量之间没有发现显著的相关性。具有窄发射线的PMS恒星的Ca II IRT线的表面通量与恒星热光度R'_IRT之比与年轻疏散星团中低质量恒星的最大R'_IRT一样大。这一结果表明，即使在经典的金牛座T星阶段，大多数PMS恒星也具有类似于零年龄主序星的色球活动。
{"title":"Measurements of the Ca ii infrared triplet emission lines of pre-main-sequence stars","authors":"Mai Yamashita, Y. Itoh, Y. Takagi","doi":"10.1093/pasj/psaa073","DOIUrl":"https://doi.org/10.1093/pasj/psaa073","url":null,"abstract":"We investigated the chromospheric activity of 60 pre-main-sequence (PMS) stars in four molecular clouds and five moving groups. It is considered that strong chromospheric activity is driven by the dynamo processes generated by the stellar rotation. In contrast, several researchers have pointed out that the chromospheres of PMS stars are activated by mass accretion from their protoplanetary disks. In this study, the Ca II infrared triplet (IRT) emission lines were investigated utilizing medium- and high-resolution spectroscopy. The observations were conducted with Nayuta/MALLS and Subaru/HDS. Additionally, archive data obtained by Keck/HIRES, VLT/UVES, and VLT/X-Shooter was used. The small ratios of the equivalent widths indicate that Ca II IRT emission lines arise primarily in dense chromospheric regions. Seven PMS stars show broad emission lines. Among them, four PMS stars have more than one order of magnitude brighter emission line fluxes compared to the low-mass stars in young open clusters. The four PMS stars have a high mass accretion rate, which indicates that the broad and strong emission results from a large mass accretion. However, most PMS stars exhibit narrow emission lines. No significant correlation was found between the accretion rate and flux of the emission line. The ratios of the surface flux of the Ca II IRT lines to the stellar bolometric luminosity, R'_IRT, of the PMS stars with narrow emission lines are as large as the largest R'_IRT of the low-mass stars in the young open clusters. This result indicates that most PMS stars, even in the classical T Tauri star stage, have chromospheric activity similar to zero-age main-sequence stars.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81113626","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}
V. Ksoll, Lynton Ardizzone, R. Klessen, U. Köthe, E. Sabbi, M. Robberto, Dimitrios M. Gouliermis, C. Rother, P. Zeidler, M. Gennaro
Photometric surveys with the Hubble Space Telescope (HST) remain one of the most efficient tools in astronomy to study stellar clusters with high resolution and deep coverage. Estimating physical parameters of their constituents from photometry alone, however, is not a trivial task. Leveraging sophisticated stellar evolution models one can simulate observations and characterise stars and clusters. Due to observational constraints, such as extinction, photometric uncertainties and low filter coverage, as well as intrinsic effects of stellar evolution, this inverse problem suffers from degenerate mappings between the observable and physical parameter space that are difficult to detect and break. We employ a novel deep learning approach called conditional invertible neural network (cINN) to solve the inverse problem of predicting physical parameters from photometry on an individual star basis. Employing latent variables to encode information otherwise lost in the mapping from physical to observable parameter space, the cINN can predict full posterior distributions for the underlying physical parameters. We build this approach on carefully curated synthetic data sets derived from the PARSEC stellar evolution models. For simplicity we only consider single metallicity populations and neglect all effects except extinction. We benchmark our approach on HST data of two well studied stellar clusters, Westerlund 2 and NGC 6397. On the synthetic data we find overall excellent performance, with age being the most difficult parameter to constrain. For the real observations we retrieve reasonable results and are able to confirm previous findings for Westerlund 2 on cluster age ($1.04_{-0.90}^{+8.48},mathrm{Myr} $), mass segregation, and the stellar initial mass function.
{"title":"Stellar parameter determination from photometry using invertible neural networks","authors":"V. Ksoll, Lynton Ardizzone, R. Klessen, U. Köthe, E. Sabbi, M. Robberto, Dimitrios M. Gouliermis, C. Rother, P. Zeidler, M. Gennaro","doi":"10.1093/mnras/staa2931","DOIUrl":"https://doi.org/10.1093/mnras/staa2931","url":null,"abstract":"Photometric surveys with the Hubble Space Telescope (HST) remain one of the most efficient tools in astronomy to study stellar clusters with high resolution and deep coverage. Estimating physical parameters of their constituents from photometry alone, however, is not a trivial task. Leveraging sophisticated stellar evolution models one can simulate observations and characterise stars and clusters. Due to observational constraints, such as extinction, photometric uncertainties and low filter coverage, as well as intrinsic effects of stellar evolution, this inverse problem suffers from degenerate mappings between the observable and physical parameter space that are difficult to detect and break. We employ a novel deep learning approach called conditional invertible neural network (cINN) to solve the inverse problem of predicting physical parameters from photometry on an individual star basis. Employing latent variables to encode information otherwise lost in the mapping from physical to observable parameter space, the cINN can predict full posterior distributions for the underlying physical parameters. We build this approach on carefully curated synthetic data sets derived from the PARSEC stellar evolution models. For simplicity we only consider single metallicity populations and neglect all effects except extinction. We benchmark our approach on HST data of two well studied stellar clusters, Westerlund 2 and NGC 6397. On the synthetic data we find overall excellent performance, with age being the most difficult parameter to constrain. For the real observations we retrieve reasonable results and are able to confirm previous findings for Westerlund 2 on cluster age ($1.04_{-0.90}^{+8.48},mathrm{Myr} $), mass segregation, and the stellar initial mass function.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86386596","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 : 2020-07-14DOI: 10.1051/0004-6361/202038913
J. Großschedl, J. Alves, S. Meingast, Gabor Herbst-Kiss
We present the first study of the 3D dynamics of the gas in the entire Southern Orion cloud complex. We used the YSO's proper motions from Gaia as a proxy for the gas proper motion, together with gas radial velocities from archival CO data, to compute the space motion of the different star-forming clouds in the complex, including sub-regions in Orion A, Orion B, and two outlying cometary clouds. From the analysis of the cloud's orbits in space and time we find that they were closest about 6 Myr ago and are moving radially away from roughly the same region in space. This coherent 100-pc scale radial motion supports a scenario where the entire complex is reacting to a major feedback event that we name the Orion-6 event. This event, that we tentatively associate with the recently discovered Orion X population, shaped the distribution and kinematics of the gas we observe today, although it is unlikely to have been the sole major feedback event in the region. We argue that the dynamics of most of the YSOs carry the memory of the feedback-driven star formation history in Orion and that the majority of the young stars in this complex are a product of large-scale triggering, that can raise the star formation rate by at least an order of magnitude, as in the case of the Orion A's Head (the Integral Shape Filament). Our results imply that at the genesis of the Orion Nebula Cluster (and NGC2023/2024 in Orion B) lies a feedback/compression/triggering process.
{"title":"3D dynamics of the Orion cloud complex","authors":"J. Großschedl, J. Alves, S. Meingast, Gabor Herbst-Kiss","doi":"10.1051/0004-6361/202038913","DOIUrl":"https://doi.org/10.1051/0004-6361/202038913","url":null,"abstract":"We present the first study of the 3D dynamics of the gas in the entire Southern Orion cloud complex. We used the YSO's proper motions from Gaia as a proxy for the gas proper motion, together with gas radial velocities from archival CO data, to compute the space motion of the different star-forming clouds in the complex, including sub-regions in Orion A, Orion B, and two outlying cometary clouds. From the analysis of the cloud's orbits in space and time we find that they were closest about 6 Myr ago and are moving radially away from roughly the same region in space. This coherent 100-pc scale radial motion supports a scenario where the entire complex is reacting to a major feedback event that we name the Orion-6 event. This event, that we tentatively associate with the recently discovered Orion X population, shaped the distribution and kinematics of the gas we observe today, although it is unlikely to have been the sole major feedback event in the region. We argue that the dynamics of most of the YSOs carry the memory of the feedback-driven star formation history in Orion and that the majority of the young stars in this complex are a product of large-scale triggering, that can raise the star formation rate by at least an order of magnitude, as in the case of the Orion A's Head (the Integral Shape Filament). Our results imply that at the genesis of the Orion Nebula Cluster (and NGC2023/2024 in Orion B) lies a feedback/compression/triggering process.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84135958","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}
We present an analysis of the starspot evolution, the surface differential rotation (SDR), the correlation between chromospheric activity indicators and the spatial connection between chromospheric and photospheric activities on the active star Kepler-411, using time series photometry over 4 years from Kepler, and spectroscopic data from Keck I 10-m telescope and Lijiang 2.4-m telescope. We constructed the light curve by re-performing photometry and reduction from the Target Pixel Files and Cotrending Basis Vectors with a manually redefined aperture using the software PyKE3. An efficient program, GEMC_LCM, was developed to apply a two-spots model to chosen light curve segments with three spot groups at fixed latitudes (30, 45), (30, 60) and (45, 60). We found a periodic variation of the starspots at period of about 660 days which independs on spot latitudes, and estimated the lower limit of SDR as $P_{text{eq}} = 9.7810(0.0169)$ days and $alpha = 0.1016(0.0023)$. Simultaneously, the relative variations of chromospheric activity indicators were derived by subtracting the overall mean spectrum from individual spectrum. It is found that Ca II H and K emissions are strongly correlated with each other, and there also exists a correlation between H$alpha$ and Ca II H & K emissions, with large dispersion, in accordance with previous results. Furthermore we find the correlation between Ca II H and K emissions is different in 2011 and 2012. The chromospheric emission variation shows a highly spatial anti-correlation with the light curve, suggesting a spatial connection between the chromospheric active region and spot region.
本文利用开普勒望远镜4年的时间序列光度测量和Keck I 10-m望远镜和丽江2.4-m望远镜的光谱数据，分析了开普勒-411主星上的星斑演化、表面微分旋转(SDR)、色球活动指标之间的相关性以及色球活动和光球活动之间的空间联系。我们使用PyKE3软件，通过手动重新定义孔径，重新执行测光和还原目标像素文件和Cotrending Basis Vectors，构建了光曲线。开发了一个高效的程序GEMC_LCM，用于在固定纬度(30,45)，(30,60)和(45,60)上选择具有三个光斑组的两个光斑模型。我们发现这些恒星黑子的周期变化约为660天，与黑子纬度无关，并估计SDR的下限为$P_{text{eq}} = 9.7810(0.0169)$ days， $alpha = 0.1016(0.0023)$。同时，用单个光谱减去总体平均光谱，得到色球活性指标的相对变化。发现Ca II H和K发射之间存在强相关关系，H$alpha$与Ca II H & K发射之间也存在相关性，且色散较大，与前人的结果一致。此外，我们发现2011年和2012年Ca、H和K排放量的相关性不同。色球发射变化与光曲线呈高度空间反相关，表明色球活跃区与光斑区之间存在空间联系。
{"title":"Starspot evolution, differential rotation, and correlation between chromospheric and photospheric activities on Kepler-411","authors":"Fukun Xu, S. Gu, P. Ioannidis","doi":"10.1093/mnras/staa3793","DOIUrl":"https://doi.org/10.1093/mnras/staa3793","url":null,"abstract":"We present an analysis of the starspot evolution, the surface differential rotation (SDR), the correlation between chromospheric activity indicators and the spatial connection between chromospheric and photospheric activities on the active star Kepler-411, using time series photometry over 4 years from Kepler, and spectroscopic data from Keck I 10-m telescope and Lijiang 2.4-m telescope. We constructed the light curve by re-performing photometry and reduction from the Target Pixel Files and Cotrending Basis Vectors with a manually redefined aperture using the software PyKE3. An efficient program, GEMC_LCM, was developed to apply a two-spots model to chosen light curve segments with three spot groups at fixed latitudes (30, 45), (30, 60) and (45, 60). We found a periodic variation of the starspots at period of about 660 days which independs on spot latitudes, and estimated the lower limit of SDR as $P_{text{eq}} = 9.7810(0.0169)$ days and $alpha = 0.1016(0.0023)$. Simultaneously, the relative variations of chromospheric activity indicators were derived by subtracting the overall mean spectrum from individual spectrum. It is found that Ca II H and K emissions are strongly correlated with each other, and there also exists a correlation between H$alpha$ and Ca II H & K emissions, with large dispersion, in accordance with previous results. Furthermore we find the correlation between Ca II H and K emissions is different in 2011 and 2012. The chromospheric emission variation shows a highly spatial anti-correlation with the light curve, suggesting a spatial connection between the chromospheric active region and spot region.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85897930","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 : 2020-07-09DOI: 10.1051/0004-6361/201935642
M. Prišegen
The population of Be/X-ray binaries shows strong evidence of bimodality, especially in the spin period of neutron stars. Several physical mechanisms may produce this bimodality. The most favored candidate mechanisms are two distinct supernova channels or different accretion modes of the neutron stars in Be/X-ray binaries. Investigating the kinematics of these systems may provide some additional insight into the physics of this bimodality. If the two Be/X-ray binary subpopulations arise from two distinct supernova types, then the two subpopulations should have different peculiar (systemic) velocities. This can be tested either directly, by measuring the velocity of the system, or indirectly, by measuring the position of the system with respect to its birthplace. Using the most recent Gaia dataset and the newest catalogs of Small Magellanic Cloud (SMC) star clusters, we analyzed the tangential peculiar velocities of Be/X-ray binaries in the Galaxy and the positions of Be/X-ray binaries in the SMC. We used the distance of the system from the nearest young star cluster as a proxy to the tangential velocity of the system. We applied statistical testing to investigate whether the two subpopulations that are divided by the spin of the neutron star are also kinematically distinct. There is evidence that the two subpopulations are indeed kinematically distinct. However, the tangential peculiar velocities of the two subpopulations are the reverse from what is expected from the distinct supernova channel hypothesis. We find some marginal evidence ($p approx$~0.005) that the Galactic Be/X-ray binaries from the short-spin subpopulation have systematically higher peculiar velocities than the systems from the long-spin subpopulation. The same effect, but weaker, is also recovered for the SMC Be/X-ray binaries for all considered cluster catalogs.
{"title":"Kinematic distinction of the two subpopulations of X-ray pulsars","authors":"M. Prišegen","doi":"10.1051/0004-6361/201935642","DOIUrl":"https://doi.org/10.1051/0004-6361/201935642","url":null,"abstract":"The population of Be/X-ray binaries shows strong evidence of bimodality, especially in the spin period of neutron stars. Several physical mechanisms may produce this bimodality. The most favored candidate mechanisms are two distinct supernova channels or different accretion modes of the neutron stars in Be/X-ray binaries. Investigating the kinematics of these systems may provide some additional insight into the physics of this bimodality. If the two Be/X-ray binary subpopulations arise from two distinct supernova types, then the two subpopulations should have different peculiar (systemic) velocities. This can be tested either directly, by measuring the velocity of the system, or indirectly, by measuring the position of the system with respect to its birthplace. Using the most recent Gaia dataset and the newest catalogs of Small Magellanic Cloud (SMC) star clusters, we analyzed the tangential peculiar velocities of Be/X-ray binaries in the Galaxy and the positions of Be/X-ray binaries in the SMC. We used the distance of the system from the nearest young star cluster as a proxy to the tangential velocity of the system. We applied statistical testing to investigate whether the two subpopulations that are divided by the spin of the neutron star are also kinematically distinct. There is evidence that the two subpopulations are indeed kinematically distinct. However, the tangential peculiar velocities of the two subpopulations are the reverse from what is expected from the distinct supernova channel hypothesis. We find some marginal evidence ($p approx$~0.005) that the Galactic Be/X-ray binaries from the short-spin subpopulation have systematically higher peculiar velocities than the systems from the long-spin subpopulation. The same effect, but weaker, is also recovered for the SMC Be/X-ray binaries for all considered cluster catalogs.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80022589","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 : 2020-07-08DOI: 10.1103/PhysRevFluids.5.124501
J. Fuentes, A. Cumming
We study the formation and evolution of a convective layer when a stably-stratified fluid with a composition gradient is cooled from above. We perform a series of 2D simulations using the Bousinessq approximation with Prandtl number ranging from Pr = 0.1 to 7, extending previous work on salty water to low Pr. We show that the evolution of the convection zone is well-described by an entrainment prescription in which a fixed fraction of the kinetic energy of convective motions is used to mix fluid at the interface with the stable layer. We measure the entrainment efficiency and find that it grows with decreasing Prandtl number or increased applied heat flux. The kinetic energy flux that determines the entrainment rate is a small fraction of the total convective luminosity. In this time-dependent situation, the density ratio at the interface is driven to a narrow range that depends on the value of Pr, and with low enough values that advection dominates the interfacial transport. We characterize the interfacial flux ratio and how it depends on the interface stability. We present an analytic model that accounts for the growth of the convective layer with two parameters, the entrainment efficiency and the interfacial heat transport, both of which can be measure from the simulations.
{"title":"Penetration of a cooling convective layer into a stably-stratified composition gradient: Entrainment at low Prandtl number","authors":"J. Fuentes, A. Cumming","doi":"10.1103/PhysRevFluids.5.124501","DOIUrl":"https://doi.org/10.1103/PhysRevFluids.5.124501","url":null,"abstract":"We study the formation and evolution of a convective layer when a stably-stratified fluid with a composition gradient is cooled from above. We perform a series of 2D simulations using the Bousinessq approximation with Prandtl number ranging from Pr = 0.1 to 7, extending previous work on salty water to low Pr. We show that the evolution of the convection zone is well-described by an entrainment prescription in which a fixed fraction of the kinetic energy of convective motions is used to mix fluid at the interface with the stable layer. We measure the entrainment efficiency and find that it grows with decreasing Prandtl number or increased applied heat flux. The kinetic energy flux that determines the entrainment rate is a small fraction of the total convective luminosity. In this time-dependent situation, the density ratio at the interface is driven to a narrow range that depends on the value of Pr, and with low enough values that advection dominates the interfacial transport. We characterize the interfacial flux ratio and how it depends on the interface stability. We present an analytic model that accounts for the growth of the convective layer with two parameters, the entrainment efficiency and the interfacial heat transport, both of which can be measure from the simulations.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86159191","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}
We have examined the optical/X-ray light curves of seven well-observed recurrent novae, V745 Sco, M31N 2008-12a, LMC N 1968, U Sco, RS Oph, LMC N 2009a, T Pyx, and one recurrent nova candidate LMC N 2012a. Six novae out of the eight show a simple relation that the duration of supersoft X-ray source (SSS) phase is 0.70 times the total duration of the outburst ($=$ X-ray turnoff time), i.e., $t_{rm SSS}=0.70 t_{rm off}$, the total duration of which ranges from 10 days to 260 days. These six recurrent novae show a broad rectangular X-ray light curve shape, first half a period of which is highly variable in the X-ray count rate. The SSS phase corresponds also to an optical plateau phase that indicates a large accretion disk irradiated by a hydrogen-burning WD. The other two recurrent novae, T Pyx and V745 Sco, show a narrow triangular shape of X-ray light curve without an optical plateau phase. Their relations between $t_{rm SSS}$ and $t_{rm off}$ are rather different from the above six recurrent novae. We also present theoretical SSS durations for recurrent novae with various WD masses and stellar metallicities ($Z=$0.004, 0.01, 0.02, and 0.05) and compare with observed durations of these recurrent novae. We show that the SSS duration is a good indicator of the WD mass in the recurrent novae with a broad rectangular X-ray light curve shape.
我们研究了7颗观测良好的复发新星V745 Sco、M31N 2008-12a、LMC N 1968、U Sco、RS Oph、LMC N 2009a、T Pyx和一颗候选复发新星LMC N 2012a的光学/ x射线光曲线。8颗新星中有6颗表现出一个简单的关系，即超软x射线源(SSS)相位的持续时间是爆发总持续时间的0.70倍($=$ x射线关闭时间)，即$t_{rm SSS}=0.70 t_{rm关闭}$，爆发总持续时间从10天到260天不等。这6颗复发新星呈现出宽的矩形x射线光曲线形状，其前半周期的x射线计数率变化很大。SSS相位也与一个光学平台相对应，这表明一个大的吸积盘被氢燃烧的WD照射。另外两颗复发新星T Pyx和V745 Sco均呈现出窄三角形的x射线光曲线，没有光学平台相。它们在$t_{rm SSS}$和$t_{rm off}$之间的关系与上述六个复发新星有很大的不同。我们还提出了具有不同WD质量和恒星金属丰度的复发新星的理论SSS持续时间($Z=$0.004, 0.01, 0.02和0.05)，并与观测到的这些复发新星的持续时间进行了比较。我们发现SSS持续时间可以很好地指示复发新星的WD质量，具有宽的矩形x射线光曲线形状。
{"title":"Supersoft X-ray phases of recurrent novae as an indicator of their white dwarf masses","authors":"M. Kato, I. Hachisu","doi":"10.1093/pasj/psaa071","DOIUrl":"https://doi.org/10.1093/pasj/psaa071","url":null,"abstract":"We have examined the optical/X-ray light curves of seven well-observed recurrent novae, V745 Sco, M31N 2008-12a, LMC N 1968, U Sco, RS Oph, LMC N 2009a, T Pyx, and one recurrent nova candidate LMC N 2012a. Six novae out of the eight show a simple relation that the duration of supersoft X-ray source (SSS) phase is 0.70 times the total duration of the outburst ($=$ X-ray turnoff time), i.e., $t_{rm SSS}=0.70 t_{rm off}$, the total duration of which ranges from 10 days to 260 days. These six recurrent novae show a broad rectangular X-ray light curve shape, first half a period of which is highly variable in the X-ray count rate. The SSS phase corresponds also to an optical plateau phase that indicates a large accretion disk irradiated by a hydrogen-burning WD. The other two recurrent novae, T Pyx and V745 Sco, show a narrow triangular shape of X-ray light curve without an optical plateau phase. Their relations between $t_{rm SSS}$ and $t_{rm off}$ are rather different from the above six recurrent novae. We also present theoretical SSS durations for recurrent novae with various WD masses and stellar metallicities ($Z=$0.004, 0.01, 0.02, and 0.05) and compare with observed durations of these recurrent novae. We show that the SSS duration is a good indicator of the WD mass in the recurrent novae with a broad rectangular X-ray light curve shape.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86621161","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 : 2020-07-07DOI: 10.1007/978-3-030-55336-4_34
Nuno Moedas, B. Nsamba, M. T. Clara
{"title":"Asteroseismic Stellar Modelling: Systematics from the Treatment of the Initial Helium Abundance","authors":"Nuno Moedas, B. Nsamba, M. T. Clara","doi":"10.1007/978-3-030-55336-4_34","DOIUrl":"https://doi.org/10.1007/978-3-030-55336-4_34","url":null,"abstract":"","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90529849","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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