scholarly journals Relations Between He I λ10830 Absorption Strength and Stellar Activity Amongst Dwarf Stars

2016 ◽  
Vol 33 ◽  
Author(s):  
Graeme H. Smith
Keyword(s):  
High Resolution ◽  
Transition Region ◽  
Spectral Type ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Stellar Activity ◽  
Dwarf Stars ◽  
X Ray ◽  
Coronal Activity ◽  
Show Evidence

AbstractCorrelations are identified between the strength of the λ10830 He I triplet line and the following tracers of stellar activity amongst FGK dwarfs with colours of (B − V) > 0.47: coronal soft X-ray emission, emission in the λ1549 C IV and λ1335 C II lines originating from the transition region, and Ca II H and K emission from the chromosphere. No such correlations are present amongst dwarfs with spectral type earlier than F6. In addition, G and K dwarfs with strong triplet lines show evidence of excess flux in the GALEX FUV band compared to weak-triplet-line dwarfs. The X-ray spectra of late-F, G, and K dwarfs with He I triplets stronger than 160 mÅ have greater values of the ROSAT hardness ratio HR1 than are typical of weak-triplet dwarfs in the same range of spectral type. In other words, dwarfs later than F7V with strong He I triplet lines tend towards harder 0.1–2.0 keV X-ray spectra than weak-triplet dwarfs, although values of HR1 ~ −0.2 to +0.1 can still be encountered amongst a minority of weak-He-triplet stars. As regards, FGK main sequence stars the observational data on the λ10830 triplet line remains sparse. Progress could be made through spectroscopy of high resolution for samples of hundreds of stars, selected on the basis of having other measures of chromospheric and coronal activity available.

A Discussion on astronomy in the ultraviolet - The ultraviolet spectrum of B-type supergiants

1975 ◽  
Vol 279 (1289) ◽  
pp. 429-442
Keyword(s):  
High Resolution ◽  
Spectral Type ◽  
Main Sequence ◽  
Ultraviolet Spectrum ◽  
Absorption Lines ◽  
Light Elements ◽  
Main Sequence Stars ◽  
Complete Identification ◽  
Constant Strength

The broad, steep-sided absorption lines in B-type supergiant spectra are stronger than the absorption lines in main-sequence stars. In addition to lines from the second, third and fourth spectra of the light elements and the metals there is a broad, pointed feature at 1720 A which has constant strength in the B-type supergiants regardless of spectral type. The complete identification of this blend is not known. At high resolution the ultraviolet resonance lines of C iv, N v, Si hi and Si iv in the spectra of OB supergiants are shortward displaced by velocities up to 1800 km s-1 indicating the presence of an escaping atmosphere. At type B5 the expanding atmosphere is moving at about 120 km s-1 which means that the material is probably brought to rest before it escapes from the star. Evidence is presented of the presence of a stationary shell around the B5Ia supergiant q Canis Majoris as well as a slowly expanding atmosphere.

scholarly journals Rotation-Activity Connections in Main Sequence Binaries

1983 ◽  
Vol 71 ◽  
pp. 475-477 ◽  
Author(s):  
O. Vilhu ◽  
S.M. Rucinski
Keyword(s):  
Transition Region ◽  
Main Sequence ◽  
Orbit Coupling ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Main Sequence Stars ◽  
X Ray

We have studied transition-region (NV + SilV + CIV) and chromospheric (MgII) emission observed with IUE (Vilhu and Rucinski, 1982; Rucinski and Vilhu, 1982; Ayres et al., 1981) together with coronal (soft X-ray) emission observed with the Einstein satellite (Cruddace and Dupree, 1982; Walter, 1982) for contact (W UMa) and detached main sequence binaries. The components are main sequence stars (or near ms) and rapid rotators due to spin-orbit coupling. They can thus be expected to give information of dynamo-processes in rapid rotators, although the binary effects clearly produce extra complications in this discussion.

scholarly journals The Structure and Energy Balance in Main Sequence Stars

1983 ◽  
Vol 71 ◽  
pp. 61-65
Author(s):  
C. Jordan ◽  
T.R. Ayres ◽  
A. Brown
Keyword(s):  
Energy Balance ◽  
High Resolution ◽  
Thermal Conduction ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
X Ray

ABSTRACTHigh-resolution spectra obtained with the IUE satellite have been used to study the structure and energy balance in the main sequence stars ξ Boo A, α Cen A, α Cen B and ε Eri. The EUV observations are combined with X-ray fluxes to predict the coronal temperatures, the electron pressures and energy lost or transferred by radiation and thermal conduction

scholarly journals Observations of Magnetic Fields on Late-Type Stars

1983 ◽  
Vol 102 ◽  
pp. 1-22
Author(s):  
Geoffrey W. Marcy
Keyword(s):  
Magnetic Fields ◽  
Flux Tube ◽  
Spectral Type ◽  
Transport Mechanism ◽  
Main Sequence ◽  
Energy Transport ◽  
Slow Mode ◽  
Late Type ◽  
Main Sequence Stars ◽  
X Ray

The “Robinson” method for measuring magnetic fields on solar- and late-type stars is reviewed. The results of such measurements for a sample of 29 G and K main-sequence stars are presented. The area covering-factors of magnetic regions are greater in the K dwarfs than in the G dwarfs, but no spectral-type dependence is found for the field strengths, contrary to expectations of some flux-tube models. The dependence of Ca II H and K emission on magnetic fields and Teff is consistent with theoretical expectations for “slow-mode” mhd wave-generation rates, but inconsistent with those of other mhd modes. Coronal soft X-ray fluxes correlate well with the magnetic fields, and it is argued that Alfvén waves are the likely energy-transport mechanism. Surface magnetic fluxes vary with rotation as , depending on spectral type.

scholarly journals Magnetic Activity of Pre-main Sequence Stars near the Stellar-Substellar Boundary

2015 ◽  
Vol 10 (S314) ◽  
pp. 126-127
Author(s):  
David Principe ◽  
Joel. H. Kastner ◽  
David Rodriguez
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Brown Dwarfs ◽  
Magnetic Activity ◽  
Main Sequence Stars ◽  
Coronal Emission ◽  
Low Mass Stars ◽  
X Ray ◽  
Low Mass ◽  
Age Range

AbstractX-ray observations of pre-main sequence (pre-MS) stars of M-type probe coronal emission and offer a means to investigate magnetic activity at the stellar-substellar boundary. Recent observations of main sequence (MS) stars at this boundary display a decrease in fractional X-ray luminosity (LX/Lbol) by almost two orders of magnitude for spectral types M7 and later. We investigate magnetic activity and search for a decrease in X-ray emission in the pre-MS progenitors of these MS stars. We present XMM-Newton X-ray observations and preliminary results for ~10 nearby (30-70 pc), very low mass pre-MS stars in the relatively unexplored age range of 10-30 Myr. We compare the fractional X-ray luminosities of these 10-30 Myr old stars to younger (1-3 Myr) pre-MS brown dwarfs and find no dependence on spectral type or age suggesting that X-ray activity declines at an age later than ~30 Myr in these very low-mass stars.

scholarly journals Stellar 5 min Oscillations

1983 ◽  
Vol 66 ◽  
pp. 469-486
Author(s):  
Jørgen Christensen-Dalsgaard ◽  
Søren Frandsen
Keyword(s):  
Spectral Type ◽  
Main Sequence ◽  
Total Flux ◽  
The Sun ◽  
Major Fraction ◽  
Main Sequence Stars ◽  
Red Supergiants

AbstractEstimates are given for the amplitudes of stochastically excited oscillations in Main Sequence stars and cool giants; these were obtained using the equipartition between convective and pulsational energy which was originally proposed by Goldreich and Keeley. The amplitudes of both velocity and luminosity perturbation generally increase with increasing mass along the Main Sequence as long as convection transports a major fraction of the total flux, and the amplitudes also increase with the age of the model. The 1.5 Mʘ ZAMS model, of spectral type F0, has velocity amplitudes ten times larger than those found in the Sun. For very luminous red supergiants luminosity amplitudes of up to about 0ṃ.1 are predicted, in rough agreement with observations presented by Maeder.

scholarly journals IN-SYNC I: HOMOGENEOUS STELLAR PARAMETERS FROM HIGH-RESOLUTION APOGEE SPECTRA FOR THOUSANDS OF PRE-MAIN SEQUENCE STARS

2014 ◽  
Vol 794 (2) ◽  
pp. 125 ◽  
Author(s):  
Michiel Cottaar ◽  
Kevin R. Covey ◽  
Michael R. Meyer ◽  
David L. Nidever ◽  
Keivan G. Stassun ◽  
...  
Keyword(s):  
High Resolution ◽  
Main Sequence ◽  
Main Sequence Stars

scholarly journals Activity and rotation of the X-ray emitting Kepler stars

2019 ◽  
Vol 628 ◽  
pp. A41 ◽  
Author(s):  
D. Pizzocaro ◽  
B. Stelzer ◽  
E. Poretti ◽  
S. Raetz ◽  
G. Micela ◽  
...  
Keyword(s):  
White Light ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Light Curves ◽  
Late Type ◽  
Main Sequence Stars ◽  
Photometric Variability ◽  
X Ray ◽  
Rotation Periods ◽  
Flare Frequency

The relation between magnetic activity and rotation in late-type stars provides fundamental information on stellar dynamos and angular momentum evolution. Rotation-activity studies found in the literature suffer from inhomogeneity in the measurement of activity indexes and rotation periods. We overcome this limitation with a study of the X-ray emitting, late-type main-sequence stars observed by XMM-Newton and Kepler. We measured rotation periods from photometric variability in Kepler light curves. As activity indicators, we adopted the X-ray luminosity, the number frequency of white-light flares, the amplitude of the rotational photometric modulation, and the standard deviation in the Kepler light curves. The search for X-ray flares in the light curves provided by the EXTraS (Exploring the X-ray Transient and variable Sky) FP-7 project allows us to identify simultaneous X-ray and white-light flares. A careful selection of the X-ray sources in the Kepler field yields 102 main-sequence stars with spectral types from A to M. We find rotation periods for 74 X-ray emitting main-sequence stars, 20 of which do not have period reported in the previous literature. In the X-ray activity-rotation relation, we see evidence for the traditional distinction of a saturated and a correlated part, the latter presenting a continuous decrease in activity towards slower rotators. For the optical activity indicators the transition is abrupt and located at a period of ~10 d but it can be probed only marginally with this sample, which is biased towards fast rotators due to the X-ray selection. We observe seven bona-fide X-ray flares with evidence for a white-light counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of ~0.15 d−1, consistent with the optical flare frequency obtained from the much longer Kepler time-series.

Coronal activity-rotation relations for lower main-sequence stars

1989 ◽  
Vol 344 ◽  
pp. 907 ◽  
Author(s):  
Andrea K. Dobson ◽  
Richard R. Radick
Keyword(s):  
Main Sequence ◽  
Main Sequence Stars ◽  
Coronal Activity
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