Ca II H and K and Hα, and Li Abundances in the Pleiades Late K Main-Sequence

1991 ◽  
Vol 130 ◽  
pp. 443-445
Author(s):  
R. J. García López ◽  
R. Rebolo ◽  
J. E. Beckman ◽  
A. Magazzù
Keyword(s):  
Effective Temperature ◽  
Main Sequence ◽  
Surface Coverage ◽  
Active Regions ◽  
Abundance Distribution ◽  
Main Sequence Stars ◽  
Chromospheric Activity ◽  
Wide Range ◽  
Active Stars

AbstractWe have observed seven main sequence stars in the Pleiades, with B – V between 0.98 and 1.41 (5100–3900 K), and with a wide range of rotational velocities, in Ca II H and K, Hα and have derived Li abundances. Our results, combined with literature data, indicate that the most chromospherically active stars are rapid rotators, and that at a given effective temperature the Li-rich stars show the highest chromospheric activity. A different surface coverage of active regions could influence the dichotomy observed in the Li abundance distribution.

Chromospheric activity as a function of age in main-sequence stars

1966 ◽  
Vol 24 ◽  
pp. 40-43
Author(s):  
O. C. Wilson ◽  
A. Skumanich
Keyword(s):  
Main Sequence ◽  
The Sun ◽  
Main Sequence Stars ◽  
Tentative Conclusion ◽  
Chromospheric Activity ◽  
General Field ◽  
Large Clusters

Evidence previously presented by one of the authors (1) suggests strongly that chromospheric activity decreases with age in main sequence stars. This tentative conclusion rests principally upon a comparison of the members of large clusters (Hyades, Praesepe, Pleiades) with non-cluster objects in the general field, including the Sun. It is at least conceivable, however, that cluster and non-cluster stars might differ in some fundamental fashion which could influence the degree of chromospheric activity, and that the observed differences in chromospheric activity would then be attributable to the circumstances of stellar origin rather than to age.

scholarly journals Measurements of the Ca ii infrared triplet emission lines of pre-main-sequence stars

2020 ◽  
Vol 72 (5) ◽  
Author(s):  
Mai Yamashita ◽  
Yoichi Itoh ◽  
Yuhei Takagi
Keyword(s):  
Main Sequence ◽  
Open Clusters ◽  
Emission Lines ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Chromospheric Activity ◽  
Low Mass ◽  
Pms Stars ◽  
Infrared Triplet ◽  
Narrow Emission

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 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 were 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, $R^{\prime }_{\rm IRT}$, of the PMS stars with narrow emission lines are as large as the largest $R^{\prime }_{\rm IRT}$ 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.

scholarly journals A Spectroscopic Study of Blue Stragglers in M67

2008 ◽  
Vol 4 (S252) ◽  
pp. 391-397
Author(s):  
G. Q. Liu ◽  
L. Deng ◽  
M. Chávez ◽  
E. Bertone
Keyword(s):  
Effective Temperature ◽  
Spectral Properties ◽  
Main Sequence ◽  
Open Cluster ◽  
Observational Constraints ◽  
Photometric System ◽  
Main Sequence Stars ◽  
Complete Sample ◽  
Blue Stragglers ◽  
Fitting Method

AbstractSpectrophotometric observations of the complete sample of twenty four blue stragglers (BSs) in the old galactic open cluster M67 (NGC2682) have been collected, using the Guillermo Haro Observatory in Cananea, Mexico. All the calibrated spectra were re-calibrated by the Beijing Arizona Taipei Connecticut (BATC) photometric system which includes fluxes in 11 photometric bands covering ~3600–10000 Å. The goal of the current work is to provide observational constraints on spectral properties of BSs by determining the effective temperature (Teff) and surface gravity (log g). The overall results, obtained by applying the flux fitting method, indicate that Teff and surface gravities of BSs in M67 are fully compatible with those expected for main sequence stars.

scholarly journals Characterizing planetesimal belts through the study of debris dust

2010 ◽  
Vol 6 (S276) ◽  
pp. 54-59
Author(s):  
Amaya Moro-Martín
Keyword(s):  
Solar System ◽  
Main Sequence ◽  
Planetary Systems ◽  
Dust Particles ◽  
Debris Disks ◽  
Main Sequence Stars ◽  
Wide Range ◽  
Robust Process

AbstractMain sequence stars are commonly surrounded by disks of dust. From lifetime arguments, it is inferred that the dust particles are not primordial but originate from the collision of planetesimals, similar to the asteroids, comets and KBOs in our Solar system. The presence of these debris disks around stars with a wide range of masses, luminosities, and metallicities, with and without binary companions, is evidence that planetesimal formation is a robust process that can take place under a wide range of conditions. Debris disks can help us learn about the formation, evolution and diversity of planetary systems.

scholarly journals Statistics of Stellar Variability in Kepler Data with ARC Systematics Removal

2011 ◽  
Vol 7 (S285) ◽  
pp. 364-365
Author(s):  
Amy McQuillan ◽  
Suzanne Aigrain ◽  
Stephen Roberts
Keyword(s):  
Main Sequence ◽  
Active Regions ◽  
Life Time ◽  
Characteristic Size ◽  
Proper Motions ◽  
Main Sequence Stars ◽  
Periodic Behaviour ◽  
Tentative Evidence ◽  
M Stars ◽  
F Stars

AbstractWe investigate the variability properties of main-sequence stars in the first month of Kepler data, using a new astrophysically robust systematics correction. We find that 36% appear more variable than the Sun, and confirm the trend of increasing variability with decreasing effective temperature. We define low- and high-variability samples, with a cut at twice the level of the active Sun, and compare properties of the stars belonging to each sample. We find tentative evidence that the more active stars have lower proper motions. The frequency content of the variability shows clear evidence for periodic or quasi-periodic behaviour in 16% of stars, and highlights significant differences in the nature of variability between spectral types. Most A and F stars have short periods (< 2 days) and highly sinusoidal variability, suggestive of pulsations, whilst G, K and M stars tend to have longer periods (> 5 days, with a trend towards longer periods at later spectral types) and show a mixture of periodic and stochastic variability, indicative of activity. Finally, we use autoregressive models to characterise the stochastic component of the variability, and show that its typical amplitude and time-scale increase towards later spectral types, which we interpret as an increase in the characteristic size and life-time of active regions. Full details will be published shortly.

scholarly journals Stellar models of ε Eridani constrained by stellar seismology

1988 ◽  
Vol 123 ◽  
pp. 285-286
Author(s):  
D. B. Guenther
Keyword(s):  
Binary System ◽  
Effective Temperature ◽  
Characteristic Frequency ◽  
Metal Content ◽  
Main Sequence ◽  
Rapid Rotation ◽  
Chromospheric Activity ◽  
Frequency Spacing ◽  
Stellar Models ◽  
Stellar Seismology

Because Epsilon Eridani (Z = 0.013) appears about 0.2 mag above the Z = 0.02 zero-age main sequence, zero-age models of Epsilon Eridani must be evolved off the ZAMS to ages much older than its rapid rotation and high chromospheric activity suggests. To resolve this conflict we propose that either Epsilon Eridani is part of a binary system or that its metal content has been underestimated. To test these hypotheses we use not only the stellar constraints of luminosity and effective temperature but also impose that the characteristic frequency spacing of the oscillation spectra of the models match the value observed by Noyes et al. (1984).

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