2012A&A...540A.130S


C.D.S. - SIMBAD4 rel 1.7 - 2019.11.21CET05:56:36

2012A&A...540A.130S - Astronomy and Astrophysics, volume 540A, 130-130 (2012/4-1)

Basal chromospheric flux and Maunder Minimum-type stars: the quiet-Sun chromosphere as a universal phenomenon.

SCHROEDER K.-P., MITTAG M., PEREZ MARTINEZ M.I., CUNTZ M. and SCHMITT J.H.M.M.

Abstract (from CDS):

We demonstrate the universal character of the quiet-Sun chromosphere among inactive stars (solar-type and giants). By assessing the main physical processes, we shed new light on some common observational phenomena. We discuss measurements of the solar Mt. Wilson S-index, obtained by the Hamburg Robotic Telescope around the extreme minimum year 2009, and compare the established chromospheric basal CaII K line flux to the Mt. Wilson S-index data of inactive (``flat activity'') stars, including giants. During the unusually deep and extended activity minimum of 2009, the Sun reached S-index values considerably lower than in any of its previously observed minima. In several brief periods, the Sun coincided exactly with the S-indices of inactive (``flat'', presumed Maunder Minimum-type) solar analogues of the Mt. Wilson sample; at the same time, the solar visible surface was also free of any plages or remaining weak activity regions. The corresponding minimum CaII K flux of the quiet Sun and of the presumed Maunder Minimum-type stars in the Mt. Wilson sample are found to be identical to the corresponding CaII K chromospheric basal flux limit. We conclude that the quiet-Sun chromosphere is a universal phenomenon among inactive stars. Its mixed-polarity magnetic field, generated by a local, ``fast'' turbulent dynamo finally provides a natural explanation for the minimal soft X-ray emission observed for inactive stars. Given such a local dynamo also works for giant chromospheres, albeit on longer length scales, i.e., l∝R/g, with R and g as stellar radius and surface gravity, respectively, the existence of giant spicular phenomena and the guidance of mechanical energy toward the acceleration zone of cool stellar winds along flux-tubes have now become traceable.

Abstract Copyright:

Journal keyword(s): Sun: chromosphere - Sun: faculae, plages - Sun: dynamo - Sun: corona - stars: chromospheres - stars: activity

Simbad objects: 7

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Number of rows : 7

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 * tau Cet PM* 01 44 04.0834226 -15 56 14.926552 4.43 4.22 3.50 2.88 2.41 G8V 1067 1
2 HD 43587 SB* 06 17 16.1298959119 +05 05 59.915616770 6.400 6.290   5.3   G0V 207 0
3 V* V415 Car Al* 06 49 51.3141446 -53 37 20.818154   5.323 4.408     G4II 68 0
4 * bet Crv PM* 12 34 23.2348393 -23 23 48.337453 4.17 3.52 2.64 2.03 1.59 G5IIBa0.3 237 0
5 * rho CrB PM* 16 01 02.6608052290 +33 18 12.642245533   6.01   5.0   G0+VaFe-1 574 1
6 HD 169689 Al* 18 25 38.7987210726 +08 01 55.231059632   6.545 5.665     G9II+B9V 97 0
7 * omi02 Cyg Al* 20 15 28.3216287393 +47 42 51.221859715 6.54 5.50 3.98 2.78 1.86 K7Ib-II+B1V 318 0

    Equat.    Gal    SGal    Ecl

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2019.11.21-05:56:36

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