Letter to the editor

Schrijver, J.; Šebečić, Blaženka

doi:10.1002/food.19870311029

Cited by 51 publications

(70 citation statements)

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“…As for the stars with 0.5 ≤ B − V ≤ 1.1, the upper and the lower level of activity do not exhibit any significant trend. The Sun also lies in this B − V range, and it lies closer to the low chromospheric activity boundary, also known as basal flux (Rutten 1984;Schrijver 1987;Rutten et al 1991;Mittag et al 2013;Pérez Martínez et al 2014). This is consistent with previous work by Noyes et al (1984a), except for the significant number of stars at intermediate activity level, which has not previously been reported.…”

Section: Log R Hk Conversion For Harps S Mwosupporting

confidence: 90%

Chromospheric activity catalogue of 4454 cool stars

Saikia

Marvin

Jeffers

et al. 2018

A&A

204

150

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Context. Chromospheric activity monitoring of a wide range of cool stars can provide valuable information on stellar magnetic activity and its dependence on fundamental stellar parameters such as effective temperature and rotation. Aims. We compile a chromospheric activity catalogue of 4454 cool stars from a combination of archival HARPS spectra and multiple other surveys, including the Mount Wilson data that have recently been released by the NSO. We explore the variation in chromospheric activity of cool stars along the main sequence for stars with different effective temperatures. Additionally, we also perform an activity-cycle period search and investigate its relation with rotation. Methods. The chromospheric activity index, S-index, was measured for 304 main-sequence stars from archived high-resolution HARPS spectra. Additionally, the measured and archived S-indices were converted into the chromospheric flux ratio log RHK'. The activity-cycle periods were determined using the generalised Lomb-Scargle periodogram to study the active and inactive branches on the rotation – activity-cycle period plane. Results. The global sample shows that the bimodality of chromospheric activity, known as the Vaughan-Preston gap, is not prominent, with a significant percentage of the stars at an intermediate-activity level around R'HK = −4.75. Independently, the cycle period search shows that stars can lie in the region intermediate between the active and inactive branch, which means that the active branch is not as clearly distinct as previously thought. Conclusions. The weakening of the Vaughan-Preston gap indicates that cool stars spin down from a higher activity level and settle at a lower activity level without a sudden break at intermediate activity. Some cycle periods are close to the solar value between the active and inactive branch, which suggests that the solar dynamo is most likely a common case of the stellar dynamo.

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Section: Log R Hk Conversion For Harps S Mwosupporting

confidence: 90%

Chromospheric activity catalogue of 4454 cool stars

Saikia

Marvin

Jeffers

et al. 2018

A&A

204

150

View full text Add to dashboard Cite

show abstract

“…In that picture, the flux-flux relations would have power-law slopes of unity up to the point where the surface filling by the active quanta was complete. Invoking a "basal" (fixed lower bound) flux in the Mg II emissions does flatten the X-ray-Mg n relation somewhat ( Schrijver 1987 ). It offers little help with the coronal ver-sus TZ emissions, however, where any lower limit to the C iv flux must be quite small (e.g., a Boo).…”

Section: Flux-flux Diagramsmentioning

confidence: 99%

The RIASS coronathon: Joint X-ray and ultraviolet observations of normal F-K stars

Ayres¹,

Fleming²,

Simon³

et al. 1995

ApJS

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Between 1990 August and 1991 January the ROSATjlUE All Sky Survey (RIASS) coordinated pointings by the International Ultraviolet Explorer with the continuous X-ray/EUV mapping by the Röntgensatellit. The campaign provided an unprecedented multi wavelength view of a wide variety of cosmic sources. We report findings for F-K stars, a large proportion of the RIASS targets. Forty-eight of our 91 "Coronathon" candidates were observed by the IUE during the campaign. For stars missed by the IUE, we supplemented the ROSAT survey fluxes with archival UV spectra and/or follow-on observations. In addition to the coordinated work, we examined the UV emission histories of the Coronathon stars. Several of the dwarfs show evidence for long-term variations in their Mg n A2802[/z] emissions, and C iv A1549 in a few cases, a Cen B (KO V) and o 2 Eri (Kl V) are noteworthy examples. Hertzsprung gap giants like 31 Com (GO III) and the secondary of Capelia {a Aur Ab: GO III) are relatively constant in C iv and Mg n, at least over decade timescales. Similarly, G8-K0 "Clump" giants show only modest long-term changes in their ultraviolet emissions. On the other hand, several of the "hybrid chromosphere" G and K supergiants show dramatic variability in the 1 Guest Observer, International Ultraviolet Explorer.

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“…On the other hand, even on the "magnetic" side of the boundary a relatively large proportion of the low-excitation Ca ii and Mg n emission from quiet stars like the Sun appears to arise in a " basal " chromosphere (e.g., Schrijver 1987), whose strength is independent of rotation (and thus likely derives from a nonmagnetic heating mechanism).…”

Section: Significance Of the Line Shiftsmentioning

confidence: 99%

The many faces of F stars - A rotational modulation study of Capella, Procyon, and Caph with the International Ultraviolet Explorer

Ayres

1991

ApJ

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I monitored the far-ultraviolet emissions of three bright "F" stars-the Capella secondary (a Aur Ah: GO III), Procyon (a CMi A: F5 IV-V), and Caph (ß Cas: F2 III-IV)-over one or more rotational cycles with the International Ultraviolet Explorer. Strong rotational modulations produced by isolated "active regions" are a characteristic signature of the hydromagnetic dynamo, believed to be the root of the nonclassical hot outer atmospheres-chromospheres and coronae-of late-type stars. Although all three stars are regarded as chromospherically "active" (with C iv A1549 surface flux densities up to 20 times solar), none exhibited any sensible rotational modulations, even at the high sensitivity achieved by pseudo-trailing low-dispersion spectra on the SWP camera (precisions of 2%-5% [1

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Letter to the editor

Cited by 51 publications

References 0 publications

Chromospheric activity catalogue of 4454 cool stars

Chromospheric activity catalogue of 4454 cool stars

The RIASS coronathon: Joint X-ray and ultraviolet observations of normal F-K stars

The many faces of F stars - A rotational modulation study of Capella, Procyon, and Caph with the International Ultraviolet Explorer

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