I. Pelisoli, T. Marsh, V. Dhillon, E. Breedt, A. Brown, M. Dyer, M. Green, P. Kerry, S. Littlefair, S. Parsons, D. Sahman, J. F. Wild
We present optical photometry of the cataclysmic variable LAMOST J024048.51+195226.9 taken with the high-speed, five-band CCD camera HiPERCAM on the 10.4 m Gran Telescopio Canarias (GTC). We detect pulsations originating from the spin of its white dwarf, finding a spin period of 24.9328(38)s. The pulse amplitude is of the order of 0.2% in the g-band, below the detection limits of previous searches. This detection establishes LAMOST J024048.51+195226.9 as only the second white dwarf magnetic propeller system, a twin of its long-known predecessor, AE Aquarii. At 24.93s, the white dwarf in LAMOST J024048.51+195226.9 has the shortest known spin period of any cataclysmic variable star. The white dwarf must have a mass of at least 0.7MSun to sustain so short a period. The observed faintest u-band magnitude sets an upper limit on the white dwarf's temperature of ~25000K. The pulsation amplitudes measured in the five HiPERCAM filters are consistent with an accretion spot of ~30000K covering ~2% of the white dwarf's visible area, although much hotter and smaller spots cannot be ruled out.
{"title":"Found: a rapidly spinning white dwarf in LAMOST J024048.51+195226.9","authors":"I. Pelisoli, T. Marsh, V. Dhillon, E. Breedt, A. Brown, M. Dyer, M. Green, P. Kerry, S. Littlefair, S. Parsons, D. Sahman, J. F. Wild","doi":"10.1093/mnrasl/slab116","DOIUrl":"https://doi.org/10.1093/mnrasl/slab116","url":null,"abstract":"We present optical photometry of the cataclysmic variable LAMOST J024048.51+195226.9 taken with the high-speed, five-band CCD camera HiPERCAM on the 10.4 m Gran Telescopio Canarias (GTC). We detect pulsations originating from the spin of its white dwarf, finding a spin period of 24.9328(38)s. The pulse amplitude is of the order of 0.2% in the g-band, below the detection limits of previous searches. This detection establishes LAMOST J024048.51+195226.9 as only the second white dwarf magnetic propeller system, a twin of its long-known predecessor, AE Aquarii. At 24.93s, the white dwarf in LAMOST J024048.51+195226.9 has the shortest known spin period of any cataclysmic variable star. The white dwarf must have a mass of at least 0.7MSun to sustain so short a period. The observed faintest u-band magnitude sets an upper limit on the white dwarf's temperature of ~25000K. The pulsation amplitudes measured in the five HiPERCAM filters are consistent with an accretion spot of ~30000K covering ~2% of the white dwarf's visible area, although much hotter and smaller spots cannot be ruled out.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90462575","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 : 2021-06-16DOI: 10.1051/0004-6361/202140591
M. Gupta, J. Thalmann, A. Veronig
We investigate the coronal magnetic energy and helicity budgets of ten solar ARs, around the times of large flares. In particular, we are interested in a possible relation of the derived quantities to the particular type of the flares that the AR produces, i.e., whether they are associated with a CME or they are confined. Using an optimization approach, we employ time series of 3D nonlinear force-free magnetic field models of ten ARs, covering a time span of several hours around the time of occurrence of large solar flares (GOES class M1.0 and larger). We subsequently compute the 3D magnetic vector potentials associated to the model 3D coronal magnetic field using a finite-volume method. This allows us to correspondingly compute the coronal magnetic energy and helicity budgets, as well as related (intensive) quantities such as the relative contribution of free magnetic energy, $E_{mathrm{F}}/{E}$ (energy ratio), the fraction of non-potential (current-carrying) helicity, $|H_{mathrm{J}}|/|{H_{V}}|$ (helicity ratio), and the normalized current-carrying helicity, $|H_{mathrm{J}}|/{phi^{prime}}^{2}$. The total energy and helicity budgets of flare-productive ARs (extensive parameters) cover a broad range of magnitudes, with no obvious relation to the eruptive potential of the individual ARs, i.e., whether or not a CME is produced in association with the flare. The intensive eruptivity proxies, $E_{mathrm{F}}/{E}$ and $|H_{mathrm{J}}|/|{H_{V}}|$, and $|H_{mathrm{J}}|/{phi^{prime}}^{2}$, however, seem to be distinctly different for ARs that produced CME-associated large flares compared to those which produced confined flares. For the majority of ARs in our sample, we are able to identify characteristic pre-flare magnitudes of the intensive quantities, clearly associated to subsequent CME-productivity.
{"title":"Magnetic helicity and energy budget around large confined and eruptive solar flares.","authors":"M. Gupta, J. Thalmann, A. Veronig","doi":"10.1051/0004-6361/202140591","DOIUrl":"https://doi.org/10.1051/0004-6361/202140591","url":null,"abstract":"We investigate the coronal magnetic energy and helicity budgets of ten solar ARs, around the times of large flares. In particular, we are interested in a possible relation of the derived quantities to the particular type of the flares that the AR produces, i.e., whether they are associated with a CME or they are confined. Using an optimization approach, we employ time series of 3D nonlinear force-free magnetic field models of ten ARs, covering a time span of several hours around the time of occurrence of large solar flares (GOES class M1.0 and larger). We subsequently compute the 3D magnetic vector potentials associated to the model 3D coronal magnetic field using a finite-volume method. This allows us to correspondingly compute the coronal magnetic energy and helicity budgets, as well as related (intensive) quantities such as the relative contribution of free magnetic energy, $E_{mathrm{F}}/{E}$ (energy ratio), the fraction of non-potential (current-carrying) helicity, $|H_{mathrm{J}}|/|{H_{V}}|$ (helicity ratio), and the normalized current-carrying helicity, $|H_{mathrm{J}}|/{phi^{prime}}^{2}$. The total energy and helicity budgets of flare-productive ARs (extensive parameters) cover a broad range of magnitudes, with no obvious relation to the eruptive potential of the individual ARs, i.e., whether or not a CME is produced in association with the flare. The intensive eruptivity proxies, $E_{mathrm{F}}/{E}$ and $|H_{mathrm{J}}|/|{H_{V}}|$, and $|H_{mathrm{J}}|/{phi^{prime}}^{2}$, however, seem to be distinctly different for ARs that produced CME-associated large flares compared to those which produced confined flares. For the majority of ARs in our sample, we are able to identify characteristic pre-flare magnitudes of the intensive quantities, clearly associated to subsequent CME-productivity.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80197286","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 : 2021-02-21DOI: 10.32023/0001-5237/70.4.6
J. Smak
It is commonly accepted that the periods of superhumps can be satisfactorily explained within a model involving apsidal motion of the accretion disk provided the frequency of the apsidal motion in addition to the dynamical term includes also the pressure effects. Using a larger sample of systems with reliable mass ratios it is shown, however, that this view is not true and the model requires further modifications.
{"title":"On the Periods and Nature of Superhumps","authors":"J. Smak","doi":"10.32023/0001-5237/70.4.6","DOIUrl":"https://doi.org/10.32023/0001-5237/70.4.6","url":null,"abstract":"It is commonly accepted that the periods of superhumps can be satisfactorily explained within a model involving apsidal motion of the accretion disk provided the frequency of the apsidal motion in addition to the dynamical term includes also the pressure effects. Using a larger sample of systems with reliable mass ratios it is shown, however, that this view is not true and the model requires further modifications.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72768107","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}
R. Leamon, S. McIntosh, S. Chapman, N. Watkins, Subhamoy Chatterjee, A. Title
This material is based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under Cooperative Agreement No. 1852977. RJL acknowledges support from NASA’s Living With a Star Program. We thank Phil Scherrer and J. Todd Hoeksema for their assistance with, and discussions on, the Wilcox Solar Observatory data, and Dipankar Bannerjee for assistance with the Kodaikanal Observatory data.
{"title":"Deciphering Solar Magnetic Activity. II. The Solar Cycle Clock and the Onset of Solar Minimum Conditions","authors":"R. Leamon, S. McIntosh, S. Chapman, N. Watkins, Subhamoy Chatterjee, A. Title","doi":"10.13016/M2R4TI-G532","DOIUrl":"https://doi.org/10.13016/M2R4TI-G532","url":null,"abstract":"This material is based upon work supported by the National Center for Atmospheric Research, which is a major facility sponsored \u0000by the National Science Foundation under Cooperative Agreement No. 1852977. RJL acknowledges support from NASA’s Living With a Star Program. We thank Phil Scherrer and J. Todd Hoeksema for their assistance with, and discussions on, the Wilcox Solar Observatory data, and Dipankar Bannerjee for assistance with the Kodaikanal Observatory data.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85271828","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}
N. Castro, M. Roth, P. Weilbacher, G. Micheva, A. Monreal-Ibero, A. Kelz, S. Kamann, M. Maseda, M. Wendt, T. M. C. L. F. A. Potsdam, Instituto de Astrof'isica de Canarias, U. L. Laguna, Liverpool John Moores University, Leiden University, U. Potsdam
The evolution of the most massive stars is a puzzle with many missing pieces. Statistical analyses are the key to provide anchors to calibrate theory, however performing these studies is an arduous job. The state-of-the-art integral field spectrograph MUSE has stirred up stellar astrophysicists who are excited about the capability to take spectra of up to a thousand stars in a single exposure. The excitement was even higher with the commissioning of the MUSE narrow-field-mode (NFM) that has demonstrated angular resolutions akin to the Hubble Space Telescope. We present the first mapping of the dense stellar core R136 in the Tarantula nebula based on a MUSE-NFM mosaic. We aim to deliver the first homogeneous analysis of the most massive stars in the local Universe and to explore the impact of these peculiar objects to the interstellar medium.
{"title":"Mapping the Youngest and Most Massive Stars in the Tarantula Nebula with MUSE-NFM","authors":"N. Castro, M. Roth, P. Weilbacher, G. Micheva, A. Monreal-Ibero, A. Kelz, S. Kamann, M. Maseda, M. Wendt, T. M. C. L. F. A. Potsdam, Instituto de Astrof'isica de Canarias, U. L. Laguna, Liverpool John Moores University, Leiden University, U. Potsdam","doi":"10.18727/0722-6691/5223","DOIUrl":"https://doi.org/10.18727/0722-6691/5223","url":null,"abstract":"The evolution of the most massive stars is a puzzle with many missing pieces. Statistical analyses are the key to provide anchors to calibrate theory, however performing these studies is an arduous job. The state-of-the-art integral field spectrograph MUSE has stirred up stellar astrophysicists who are excited about the capability to take spectra of up to a thousand stars in a single exposure. The excitement was even higher with the commissioning of the MUSE narrow-field-mode (NFM) that has demonstrated angular resolutions akin to the Hubble Space Telescope. We present the first mapping of the dense stellar core R136 in the Tarantula nebula based on a MUSE-NFM mosaic. We aim to deliver the first homogeneous analysis of the most massive stars in the local Universe and to explore the impact of these peculiar objects to the interstellar medium.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87699618","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 : 2021-01-18DOI: 10.20371/INAF/TECHREP/40
A. Bemporad, L. Abbo, D. Barghini, C. Benna, R. Biondo, D. Bonino, G. Capobianco, F. Carella, A. Cora, S. Fineschi, F. Frassati, D. Gardiol, S. Giordano, A. Liberatore, S. Mancuso, A. Mignone, S. Rasetti, F. Reale, A. Riva, F. Salvati, R. Susino, A. Volpicelli, L. Zangrilli
The SWELTO project is at present entirely supported by the INAF-Turin Astrophysical observatory. The SuperSID monitorwas provided as in kind contribution by University of Stanford, whose support is gratefully acknowledged.
{"title":"SWELTO - Space WEather Laboratory in Turin Observatory","authors":"A. Bemporad, L. Abbo, D. Barghini, C. Benna, R. Biondo, D. Bonino, G. Capobianco, F. Carella, A. Cora, S. Fineschi, F. Frassati, D. Gardiol, S. Giordano, A. Liberatore, S. Mancuso, A. Mignone, S. Rasetti, F. Reale, A. Riva, F. Salvati, R. Susino, A. Volpicelli, L. Zangrilli","doi":"10.20371/INAF/TECHREP/40","DOIUrl":"https://doi.org/10.20371/INAF/TECHREP/40","url":null,"abstract":"The SWELTO project is at present entirely supported by the INAF-Turin Astrophysical observatory. The SuperSID monitorwas provided as in kind contribution by University of Stanford, whose support is gratefully acknowledged.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76181683","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 : 2020-12-17DOI: 10.1051/0004-6361/202039329
M. Madjarska, J. Chae, F. Moreno-Insertis, Zhenyong Hou, D. Nóbrega-Siverio, Hannah Kwak, K. Galsgaard, Kyuhyoun Cho
We investigate the chromospheric counterpart of small-scale coronal loops constituting a coronal bright point (CBP) and its response to a photospheric magnetic-flux increase accompanied by co-temporal CBP heating. We used co-observations from the AIA and HMI/SDO, together with data from the Fast Imaging Solar Spectrograph taken in the Halpha and Ca II 8542 lines. We used a new multi-layer spectral inversion technique to derive the temporal variations of the temperature of the Halpha loops (HLs). We find that the counterpart of the CBP, as seen at chromospheric temperatures, is composed of a bundle of dark elongated features named in this work Halpha loops, which constitute an integral part of the CBP loop magnetic structure. An increase in the photospheric magnetic flux due to flux emergence is accompanied by a rise of the coronal emission of the CBP loops, that is a heating episode. We also observe enhanced chromospheric activity associated with the occurrence of new HLs and mottles. While the coronal emission and magnetic flux increases appear to be co-temporal, the response of the Halpha counterpart of the CBP occurs with a small delay of less than 3 min. A sharp temperature increase is found in one of the HLs and in one of the CBP footpoints estimated at 46% and 55% with respect to the pre-event values, also starting with a delay of less than 3~min following the coronal heating episode. The low-lying CBP loop structure remains non-potential for the entire observing period. The magnetic topological analysis of the overlying corona reveals the presence of a coronal null point at the beginning and towards the end of the heating episode. The delay in the response of the chromospheric counterpart of the CBP suggests that the heating may have occurred at coronal heights.
{"title":"The chromospheric component of coronal bright points","authors":"M. Madjarska, J. Chae, F. Moreno-Insertis, Zhenyong Hou, D. Nóbrega-Siverio, Hannah Kwak, K. Galsgaard, Kyuhyoun Cho","doi":"10.1051/0004-6361/202039329","DOIUrl":"https://doi.org/10.1051/0004-6361/202039329","url":null,"abstract":"We investigate the chromospheric counterpart of small-scale coronal loops constituting a coronal bright point (CBP) and its response to a photospheric magnetic-flux increase accompanied by co-temporal CBP heating. We used co-observations from the AIA and HMI/SDO, together with data from the Fast Imaging Solar Spectrograph taken in the Halpha and Ca II 8542 lines. We used a new multi-layer spectral inversion technique to derive the temporal variations of the temperature of the Halpha loops (HLs). We find that the counterpart of the CBP, as seen at chromospheric temperatures, is composed of a bundle of dark elongated features named in this work Halpha loops, which constitute an integral part of the CBP loop magnetic structure. An increase in the photospheric magnetic flux due to flux emergence is accompanied by a rise of the coronal emission of the CBP loops, that is a heating episode. We also observe enhanced chromospheric activity associated with the occurrence of new HLs and mottles. While the coronal emission and magnetic flux increases appear to be co-temporal, the response of the Halpha counterpart of the CBP occurs with a small delay of less than 3 min. A sharp temperature increase is found in one of the HLs and in one of the CBP footpoints estimated at 46% and 55% with respect to the pre-event values, also starting with a delay of less than 3~min following the coronal heating episode. The low-lying CBP loop structure remains non-potential for the entire observing period. The magnetic topological analysis of the overlying corona reveals the presence of a coronal null point at the beginning and towards the end of the heating episode. The delay in the response of the chromospheric counterpart of the CBP suggests that the heating may have occurred at coronal heights.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83843236","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 : 2020-12-16DOI: 10.1007/978-3-030-55336-4_33
L. Bugnet, V. Prat, S. Mathis, R. Garc'ia, S. Mathur, K. Augustson, C. Neiner, M. Thompson
{"title":"The Impact of a Fossil Magnetic Field on Dipolar Mixed-Mode Frequencies in Sub- and Red-Giant Stars","authors":"L. Bugnet, V. Prat, S. Mathis, R. Garc'ia, S. Mathur, K. Augustson, C. Neiner, M. Thompson","doi":"10.1007/978-3-030-55336-4_33","DOIUrl":"https://doi.org/10.1007/978-3-030-55336-4_33","url":null,"abstract":"","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75685582","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 : 2020-12-16DOI: 10.1051/0004-6361/202039902
M. Flores, M. J. Arancibia, R. Bustos, A. Buccino, J. Y. Galarza, N. Nuñez, P. Miquelarena, J. Alacoria, C. Saffe, P. Mauas
Context. It is well known that from 1645 to 1715 solar activity was notably low and the number of sunspots was extremely reduced. This epoch is known as the Maunder Minimum (MM). The study of stars in prolonged activity minima like the MM could help to shed light on this enigmatic epoch. Aims. To explore if the star $zeta^{2}$ Ret, which belongs to a binary system, is in a state similar to the MM. We have collected more than 430 spectra acquired between 2000 and 2019 with the HARPS, REOSC, UVES, and FEROS spectrographs. Methods. We performed a detailed long-term activity study of both components using the Mount Wilson index, which is obtained from the Ca II H&K lines. To search for signs of an activity cycle, we analyzed the resulting time-series with the Generalized Lomb-Scargle and CLEAN periodograms. Results. Our spectroscopic analysis shows a high activity level for zet01 Ret and a significant decrease in the magnetic activity cycle amplitude of $zeta^{2}$ Ret. Thus, the activity difference between both components has been slightly increased ($Delta$log (RHK) $sim$0.24 dex), when compared to the previously reported value. The long series analyzed here allowed us to recalculate and constrain the period of $zeta^{2}$ Ret to $sim$7.9 yr. We also detected a long-term activity cycle of $sim$4.2 yr in $zeta^{1}$ Ret. Conclusions. By analogy with the scenario that proposes a weak solar cycle during the MM, we suggest that activity signatures showed by $zeta^{2}$ Ret, i.e., a very low activity level when compared to its stellar companion, a notably decreasing amplitude ($sim$47%), and a cyclic behaviour, are possible evidence that this star could be in a MM state. It is, to our knowledge, the first MM candidate star detected through a highly discrepant activity behaviour in a binary system.
背景。众所周知，从1645年到1715年，太阳活动非常低，太阳黑子的数量急剧减少。这个时期被称为蒙德极小期(MM)。对像MM这样处于长期活动极小期的恒星的研究有助于揭示这个神秘的时代。目标为了探索属于双星系统的恒星$zeta^{2}$ Ret是否处于类似于MM的状态，我们收集了2000年至2019年间使用HARPS, REOSC, UVES和FEROS光谱仪获得的430多个光谱。方法。我们使用从Ca II H＆K系获得的Mount Wilson指数对这两个组分进行了详细的长期活性研究。为了寻找活动周期的迹象，我们用广义Lomb-Scargle和CLEAN周期图分析了产生的时间序列。结果。我们的光谱分析显示，zet01 Ret的活性水平较高，而$zeta^{2}$ Ret的磁活动周期幅度显著降低。因此，与先前报道的值相比，两个组分之间的活性差异略有增加($Delta$ log (RHK) $sim$ 0.24指数)。这里分析的长序列使我们能够重新计算并将$zeta^{2}$ Ret的周期限制为$sim$ 7.9年。我们还发现$zeta^{1}$ Ret的长期活动周期为$sim$ 4.2年。通过与MM期间太阳周期较弱的情景类比，我们认为$zeta^{2}$ Ret所显示的活动特征，即与它的伴星相比，其活动水平非常低，幅度明显下降($sim$ 47%), and a cyclic behaviour, are possible evidence that this star could be in a MM state. It is, to our knowledge, the first MM candidate star detected through a highly discrepant activity behaviour in a binary system.
{"title":"Detecting prolonged activity minima in binary stars","authors":"M. Flores, M. J. Arancibia, R. Bustos, A. Buccino, J. Y. Galarza, N. Nuñez, P. Miquelarena, J. Alacoria, C. Saffe, P. Mauas","doi":"10.1051/0004-6361/202039902","DOIUrl":"https://doi.org/10.1051/0004-6361/202039902","url":null,"abstract":"Context. It is well known that from 1645 to 1715 solar activity was notably low and the number of sunspots was extremely reduced. This epoch is known as the Maunder Minimum (MM). The study of stars in prolonged activity minima like the MM could help to shed light on this enigmatic epoch. \u0000Aims. To explore if the star $zeta^{2}$ Ret, which belongs to a binary system, is in a state similar to the MM. We have collected more than 430 spectra acquired between 2000 and 2019 with the HARPS, REOSC, UVES, and FEROS spectrographs. \u0000Methods. We performed a detailed long-term activity study of both components using the Mount Wilson index, which is obtained from the Ca II H&K lines. To search for signs of an activity cycle, we analyzed the resulting time-series with the Generalized Lomb-Scargle and CLEAN periodograms. \u0000Results. Our spectroscopic analysis shows a high activity level for zet01 Ret and a significant decrease in the magnetic activity cycle amplitude of $zeta^{2}$ Ret. Thus, the activity difference between both components has been slightly increased ($Delta$log (RHK) $sim$0.24 dex), when compared to the previously reported value. The long series analyzed here allowed us to recalculate and constrain the period of $zeta^{2}$ Ret to $sim$7.9 yr. We also detected a long-term activity cycle of $sim$4.2 yr in $zeta^{1}$ Ret. \u0000Conclusions. By analogy with the scenario that proposes a weak solar cycle during the MM, we suggest that activity signatures showed by $zeta^{2}$ Ret, i.e., a very low activity level when compared to its stellar companion, a notably decreasing amplitude ($sim$47%), and a cyclic behaviour, are possible evidence that this star could be in a MM state. It is, to our knowledge, the first MM candidate star detected through a highly discrepant activity behaviour in a binary system.","PeriodicalId":8493,"journal":{"name":"arXiv: Solar and Stellar Astrophysics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75247756","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 : 2020-12-15DOI: 10.1051/0004-6361/202039536
Chuan-peng Zhang, R. Launhardt, Yao Liu, J. Tobin, T. Henning
Planetary cores are thought to form in proto-planetary disks via the growth of dusty solid material. However, it is unclear how early this process begins. We study the physical structure and grain growth in the edge-on disk that surrounds the ~1 Myr old low-mass (~0.55 Msun) protostar embedded in the Bok Globule CB26 to examine how much grain growth has already occurred in the protostellar phase. We combine the SED between 0.9 ${mu}$m and 6.4 cm with high angular resolution continuum maps at 1.3, 2.9, and 8.1 mm, and use the radiative transfer code RADMC-3D to conduct a detailed modelling of the dust emission from the disk and envelope of CB 26. We infer inner and outer disk radii of around 16 au and 172$pm$22 au, respectively. The total gas mass in the disk is ~0.076 Msun, which amounts to ~14% of the mass of the central star. The inner disk contains a compact free-free emission region, which could be related to either a jet or a photoevaporation region. The thermal dust emission from the outer disk is optically thin at mm wavelengths, while the emission from the inner disk midplane is moderately optically thick. Our best-fit radiative transfer models indicate that the dust grains in the disk have already grown to pebbles with diameters of the order of 10 cm in size. Residual 8.1 mm emission suggests the presence of even larger particles in the inner disk. For the optically thin mm dust emission from the outer disk, we derive a mean opacity slope of 0.6$pm$0.4, which is consistent with the presence of large dust grains. The presence of cm-sized bodies in the CB 26 disk indicates that solids grow rapidly already during the first million years in a protostellar disk. It is thus possible that Class II disks are already seeded with large particles and may contain even planetesimals.
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