Magnetic activity based on LAMOST medium-resolution spectra and the Kepler survey

2020 ◽  
Vol 495 (1) ◽  
pp. 1252-1270 ◽  
Author(s):  
Li-yun Zhang ◽  
Liu Long ◽  
Jianrong Shi ◽  
Hong-peng Lu ◽  
Qi Gao ◽  
...  
Keyword(s):  
Rotation Period ◽  
Magnetic Activity ◽  
Physical Parameters ◽  
Late Type ◽  
Data Bases ◽  
Interesting Phenomenon ◽  
Chromospheric Activity ◽  
Medium Resolution ◽  
Hα Emission ◽  
Relationship Of

ABSTRACT Stellar magnetic activity is an interesting phenomenon in late-type stars. We use the medium-resolution spectroscopic observations of 406 069 late-type stars from LAMOST to explore their properties. We perform a statistical analysis on the magnetic activity of the stars and their associated physical parameters. Our samples are cross-matched with other data bases (LAMOST DR5, VSX, and SDSS DR12) to obtain additional observational properties. The equivalent widths (EWs) of Hα lines, an indicator of chromospheric activity, are calculated. According to the EWs of the Hα line, we detect 8816 spectra with apparent Hα emission for a total of 2115 stars among the 2 108 565 spectra analysed. Furthermore, 1521 of these stars show variability in their Hα lines. In addition, we detect 2132 flare events associated with 41 542 stars from the catalogue by cross-matching our LAMOST medium-resolution samples and the Kepler and K2 data bases. We also confirm a weak relationship of the flare amplitude with increasing Rossby number. There is a clear decease in the strength of chromospheric activity (LHα/Lbol) with increasing rotation period. Moreover, the ratio of the flare energy and stellar luminosity is found to decrease with the stellar mass.

scholarly journals Stellar Chromospheric Variability

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 440
Author(s):  
Richard de de Grijs ◽  
Devika Kamath
Keyword(s):  
Large Scale ◽  
Binary Systems ◽  
Magnetic Activity ◽  
Close Binary ◽  
Physical Parameters ◽  
Stellar Rotation ◽  
Chromospheric Activity ◽  
Recent Developments ◽  
Hα Emission ◽  
Activity Cycles

Cool stars with convective envelopes of spectral types F and later tend to exhibit magnetic activity throughout their atmospheres. The presence of strong and variable magnetic fields is evidenced by photospheric starspots, chromospheric plages and coronal flares, as well as by strong Ca ii H+K and Hα emission, combined with the presence of ultraviolet resonance lines. We review the drivers of stellar chromospheric activity and the resulting physical parameters implied by the observational diagnostics. At a basic level, we explore the importance of stellar dynamos and their activity cycles for a range of stellar types across the Hertzsprung–Russell diagram. We focus, in particular, on recent developments pertaining to stellar rotation properties, including the putative Vaughan–Preston gap. We also pay specific attention to magnetic variability associated with close binary systems, including RS Canum Venaticorum, BY Draconis, W Ursae Majoris and Algol binaries. At the present time, large-scale photometric and spectroscopic surveys are becoming generally available, thus leading to a resurgence of research into chromospheric activity. This opens up promising prospects to gain a much improved understanding of chromospheric physics and its wide-ranging impact.

scholarly journals Age, Activity and Rotation in Mid and Late-Type M Dwarfs from MEarth

2013 ◽  
Vol 9 (S302) ◽  
pp. 176-179
Author(s):  
Andrew A. West ◽  
Kolby L. Weisenburger ◽  
Jonathan Irwin ◽  
David Charbonneau ◽  
Jason Dittmann ◽  
...  
Keyword(s):  
Dimensional Space ◽  
Large Fraction ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Rotating Stars ◽  
Late Type ◽  
M Dwarfs ◽  
Magnetic Field Generation ◽  
Rotation Periods ◽  
Wide Range

AbstractUsing spectroscopic observations and photometric light curves of 280 nearby M dwarfs from the MEarth exoplanet transit survey, we examine the relationships between magnetic activity (quantified by Hα emission), rotation period, and stellar age (derived from three-dimensional space velocities). Although we have known for decades that a large fraction of mid-late-type M dwarfs are magnetically active, it was not clear what role rotation played in the magnetic field generation (and subsequent chromospheric heating). Previous attempts to investigate the relationship between magnetic activity and rotation in mid-late-type M dwarfs were hampered by the limited number of M dwarfs with measured rotation periods (and the fact that vsini measurements only probe rapid rotation). However, the photometric data from the MEarth survey allows us to probe a wide range of rotation periods for hundreds of M dwarf stars (from less than one to over 100 days). Over all M spectral types we find that magnetic activity decreases with longer rotation periods, including late-type, fully convective M dwarfs. We find that the most magnetically active (and hence, most rapidly rotating) stars are consistent with a kinematically young population, while slow-rotators are less active or inactive and appear to belong to an older, dynamically heated stellar population.

scholarly journals Surface Imaging of Late-Type Contact Binaries II: Hα Emission in AE Phe and YY Eri

2006 ◽  
Vol 2 (S240) ◽  
pp. 719-723
Author(s):  
O. Vilhu ◽  
C. Maceroni
Keyword(s):  
Active Component ◽  
Theoretical Models ◽  
Surface Imaging ◽  
Late Type ◽  
Saturation Limit ◽  
Chromospheric Activity ◽  
Type Contact ◽  
Contact Binaries ◽  
Hα Emission

AbstractWe present and discuss the Hα (λ = 6563Å) observations of the contact (W UMa type) binaries AE Phoenicis and YY Eridani, obtained in 1989, 1990 and 1995 with the CAT/CES telescope of the Southern European Observatory (ESO). In particular, we compare the intrinsic equivalent widths of both components with the NextGen theoretical models and the saturation limit. We find that the average Hα equivalent widths are close to the saturation border and that the primary components have excess Hα-emission, indicating enhanced chromospheric activity. This is compatible with both theoretical and observational suggestions that the primary is the more magnetically active component and is filled with (mostly unresolvable) dark spots and associated chromospheric plages.

scholarly journals LAMOST medium-resolution spectral survey of Galactic nebulae (LAMOST-MRS-N): subtraction of geocoronal Hα emission

2021 ◽  
Vol 21 (11) ◽  
pp. 280
Author(s):  
Wei Zhang ◽  
Hong Wu ◽  
Chao-Jian Wu ◽  
Juan-Juan Ren ◽  
Jian-Hun Chen ◽  
...  
Keyword(s):  
Linear Function ◽  
Single Line ◽  
Contamination Level ◽  
Physical Parameters ◽  
The Sun ◽  
Gradient Distribution ◽  
Solar Altitude ◽  
Medium Resolution ◽  
Hα Emission ◽  
Spectral Survey

Abstract We introduce a method of subtracting geocoronal Hα emissions from the spectra of LAMOST medium-resolution spectral survey of Galactic nebulae (LAMOST-MRS-N). The flux ratios of the Hα sky line to the adjacent OH λ6554 single line do not show a pattern or gradient distribution in a plate. More interestingly, the ratio is well correlated to solar altitude, which is the angle of the Sun relative to the Earthʼs horizon. It is found that the ratio decreases from 0.8 to 0.2 with the decreasing solar altitude from –17 to –73 degree. Based on this relation, which is described by a linear function, we can construct the Hα sky component and subtract it from the science spectrum. This method has been applied to the LAMOST-MRS-N data, and the contamination level of the Hα sky to nebula is reduced from 40% to less than 10%. The new generated spectra will significantly improve the accuracy of the classifications and the measurements of physical parameters of Galactic nebulae.

Chromospheric activity in several single late-type stars

2015 ◽  
Vol 15 (2) ◽  
pp. 252-274 ◽  
Author(s):  
Li-Yun Zhang ◽  
Qing-Feng Pi ◽  
Zhong-Zhong Zhu
Keyword(s):  
Late Type ◽  
Chromospheric Activity

scholarly journals By Draconis and RS Canum Venaticorum Stars: The Discoveries of Classical Photometry and Spectroscopy

1980 ◽  
Vol 5 ◽  
pp. 847-848 ◽  
Author(s):  
Bernard W. Bopp
Keyword(s):  
Spectroscopic Binaries ◽  
Physical Parameters ◽  
Late Type ◽  
Double Line ◽  
Strong Emission ◽  
Rs Cvn Stars ◽  
Ceti Type ◽  
The Common ◽  
Orbital Periods ◽  
Detached Binaries

Physically quite dissimilar, the BY Dra and RS CVn stars have the common characteristic of extraordinarily high levels of stellar surface activity.The RS CVn group, as defined by Hall, consists of detached binaries both components of types F, G, or K. The orbital periods are from a few days to a few weeks, and the mass ratios are generally near unity. Spectroscopically, the stars are remarkable in that they show very strong Ca II H and K emission outside eclipse. Masses and radii are known for many of these systems; physical parameters indicate these systems contain a moderately evolved subgiant, with mass slightly greater than 1 M⊚. The ages (which may be verified by data on visual companions) are a few 10 years.In contrast, the BY Dra variables are late-type dwarfs, with spectral types ranging from dK5e to dM4e. The e designation indicates the presence of Balmer emission, which is generally visible in moderate strength at Ha and only very weakly present in the blue. The BY Dra stars do exhibit strong emission at H and K, however, and also show UV Ceti-type flares. Approximately 75% of the BY Dra variables are known as double-line spectroscopic binaries.

scholarly journals Eclipsing spotted giant star with K2 and historical photometry

2018 ◽  
Vol 620 ◽  
pp. A189 ◽  
Author(s):  
K. Oláh ◽  
S. Rappaport ◽  
T. Borkovits ◽  
T. Jacobs ◽  
D. Latham ◽  
...  
Keyword(s):  
Binary System ◽  
Main Sequence ◽  
Rapid Evolution ◽  
Magnetic Activity ◽  
Primary Component ◽  
Physical Parameters ◽  
Giant Star ◽  
Eclipsing Binary ◽  
Giant Stars ◽  
Active Stars

Context. Stars can maintain their observable magnetic activity from the pre-main sequence (PMS) to the tip of the red giant branch. However, the number of known active giants is much lower than active stars on the main sequence (MS) since the stars spend only about 10% of their MS lifetime on the giant branch. Due to their rapid evolution it is difficult to estimate the stellar parameters of giant stars. A possibility for obtaining more reliable stellar parameters for an active giant arises when it is a member of an eclipsing binary system. Aims. We have discovered EPIC 211759736, an active spotted giant star in an eclipsing binary system during the Kepler K2 Campaign 5. The eclipsing nature allows us to much better constrain the stellar parameters than in most cases of active giant stars. Methods. We have combined the K2 data with archival HATNet, ASAS, and DASCH photometry, new spectroscopic radial velocity measurements, and a set of follow-up ground-based BVRCIC photometric observations, to find the binary system parameters as well as robust spot models for the giant at two different epochs. Results. We determined the physical parameters of both stellar components and provide a description of the rotational and long-term activity of the primary component. The temperatures and luminosities of both components were examined in the context of the Hertzsprung–Russell diagram. We find that both the primary and the secondary components deviate from the evolutionary tracks corresponding to their masses in the sense that the stars appear in the diagram at lower masses than their true masses. Conclusions. We further evaluate the proposition that traditional methods generally result in higher masses for active giants than what is indicated by stellar evolution tracks in the HR diagram. A possible reason for this discrepancy could be a strong magnetic field, since we see greater differences in more active stars.

scholarly journals Metode Seismik dalam Pemodelan Fisis Letusan Gunung Lumpur Bledug Kuwu

2019 ◽  
Vol 2 (2) ◽  
pp. 61-66
Author(s):  
Ahmad Fauzi Pohan ◽  
Rusnoviandi Rusnoviandi
Keyword(s):  
Wave Velocity ◽  
Physical Modeling ◽  
Vertical Component ◽  
Dominant Frequency ◽  
P Wave ◽  
Physical Parameters ◽  
S Wave ◽  
Interesting Phenomenon ◽  
Central Java ◽  
P Wave Velocity

Aktivitas gunung lumpur Bledug Kuwu di Jawa  Tengah merupakan fenomena yang menarik dikaji menggunakan pemodelan fisis. Tujuan penelitian ini adalah mengetahui parameter dari medium gunung lumpur Bledug Kuwu. Adapun pemodelan fisis yang dilakukan dengan menggunakan media fisis akuarium berukuran 59 × 59 × 37,3 cm yang diisi material dari lumpur Bledug Kuwu. Sumber letusan dihasilkan dari tekanan kompresor yang dapat diatur kedalaman (10.5, 13, dan 15.5 cm) dan sudut (30o, 45o dan 60o) sumbernya. Sensor yang digunakan geophone komponen vertikal sebanyak 3 buah dengan durasi perekaman selama 5 dan 2,5 detik. Data diambil dengan frekuensi sampel 2 dan 4 kHz untuk masing-masing durasi perekaman. Konfigurasi sumber dan geophone dibuat sesuai dengan pemodelan fisisnya. Pengukuran desnsitas lumpur menunjukkan angka sebesar 1200 kg/m3. Berdasarkan hasil analisis seismogram model fisis diperoleh kecepatan perambatan gelombang-P pada medium lumpur Bledug Kuwu adalah sebesar 48,74 m/s,dan gelombang-S sebesar 28,14 m/s dengan frekuensi dominan antara 20 sampai 25 Hz.   Bledug Kuwu mud volcano activity in Central Java is an interesting phenomenon to be studied using both physical  modeling. The objective of this study was to determine the physical parameters of the medium of Bledug Kuwu. The Physical model was an aquarium with a dimension of 59 × 59 × 37.3 cm filled with Bledug Kuwu’s mud. The eruption source is generated by a compressor pressure that can be controled both the depth(10.5, 13, and 15.5 cm) and the angel of the source (30o, 45o and 60o). The resulting seismic signals were recorded by using 3 vertical component geophones for 10 and 5 seconds durations at a frequency of 2 and 4 kHz respectivel, mud density 1200 kg/m3 . The physical modeling shows that the P-wave velocity of the Bledug Kuwu’s medium is 48.7 m/s, S-wave velocity of Bledug Kuwu’s is 28,14 m/s  with a dominant frequency of 20 to 25 Hz.

scholarly journals Physical Parameters of Late-type Contact Binaries in the Northern Catalina Sky Survey

2020 ◽  
Vol 247 (2) ◽  
pp. 50 ◽  
Author(s):  
Weijia Sun ◽  
Xiaodian Chen ◽  
Licai Deng ◽  
Richard de Grijs
Keyword(s):  
Physical Parameters ◽  
Late Type ◽  
Sky Survey ◽  
Type Contact ◽  
Contact Binaries
Sign in / Sign up

Export Citation Format

Share Document