Acoustic and magnetic wave heating in stars

Fawzy, Diaa E.; Stępień, K.; Ulmschneider, P.; Rammacher, W.; Musielak, Z. E.

doi:10.1051/0004-6361:20020253

Cited by 27 publications

(35 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A similar agreement is also found with the results presented by Hempelmann (1995) who found f mag ∝ R −0.65±0.14 0 (2) the power law coefficient found by us (averaged over all spectral types) being b = −0.72 ± 0.13. Also in a more recent study on the chromospheric emission-magnetic filling factor relation, Fawzy et al (2002) found that an exponential law best fits the dependence of the theoretical filling factor on the rotational period, at least in the rotation range they analysed (10 ≤ P ≤ 40 d). We refer the reader to Paper I for a detailed discussion about the existence of the break at P ∼ 1.1 d in the A max -P and A max -R 0 relations and about differences with respect to previous studies.…”

Section: Activity-rotation Relationmentioning

confidence: 74%

Dependence of coronal X-ray emission on spot-induced brightness variations in cool main sequence stars

Messina

Pizzolato²,

Guinan³

et al. 2003

A&A

View full text Add to dashboard Cite

Abstract.The maximum amplitude (A max ) of spot-induced brightness variations from long-term V-band photometry and the ratio L X /L bol between X-ray and bolometric luminosities are suitable indicators of the level of magnetic activity in the photosphere and in the corona of late-type stars, respectively. By using these activity indicators we investigate the dependence of coronal X-ray emission on the level of photospheric starspot activity in a homogeneous sample of low mass main sequence field and cluster stars of different ages (IC 2602, IC 4665, IC 2391, α Persei, Pleiades and Hyades). First, the activity-rotation connection at the photospheric level is re-analysed, as well as its dependence on spectral type and age. The upper envelope of A max increases monotonically with decreasing rotational period (P) and Rossby number (R 0 ) showing a break around 1.1 d that separates two rotation regimes where the starspot activity shows different behaviours. The A max -P and A max -R 0 relations are fitted with linear, exponential and power laws to look for the function which best represents the trend of the data. The highest values of A max are found among K-type stars and at the ages of α Persei and Pleiades. We also analyse the activity-rotation connection at the coronal level as well as its dependence on spectral type. The level of X-ray emission increases with increasing rotation rate up to a saturation level. The rotational period at which saturation occurs is colour-dependent and increases with advancing spectral type. Also the L X /L bol -P and L X /L bol -R 0 relations are fitted with linear, exponential and power laws to look for the best fitting function. Among the fastest rotating stars (P ≤ 0.3 d) there is evidence of super-saturation. Also the highest values of L X /L bol are found among K-type stars. Finally, the photospheric-coronal activity connection is investigated by using for the first time the largest ever sample of light curve amplitudes as indicators of the magnetic filling factor. The activity parameters L X /L bol and A max are found to be correlated with each other, thus confirming the dependence of coronal activity on photospheric magnetic fields. More precisely, the L X /L bol -A max distribution shows the presence of an upper envelope, which is constant at the L X /L bol −3.0 saturation level, and of a lower envelope. The best fit to the lower envelope is given by a power law with steepness decreasing from F-G to M spectral types. However, it is considered a tentative result, since the fit reduced chi-squares are large. Such spectral-type dependence may be related to a colour dependence of A max on the total starspot filling factor, as well as to the coronal emission being possibly more sensitive to starspot activity variations in F-and G-type than in M-type stars. The L X /L bol -A max mean values for each cluster in our sample decrease monotonically with increasing age, showing that the levels of photospheric and coronal activity evolve in time according to a single power law till the S...

show abstract

Section: Activity-rotation Relationmentioning

confidence: 74%

Dependence of coronal X-ray emission on spot-induced brightness variations in cool main sequence stars

Messina

Pizzolato²,

Guinan³

et al. 2003

A&A

View full text Add to dashboard Cite

show abstract

“…This paragraph really was written by VT). Chromospheres have to be heated, and it seems to take three sorts of input, acoustic waves, magnetic waves associated with flux tubes, plus magnetic reconnection (Fawzy et al 2002a(Fawzy et al , 2002b(Fawzy et al , 2002c.…”

Section: Stellar Activitymentioning

confidence: 99%

Astrophysics in 2002

Trimble

Aschwanden

2003

PUBL ASTRON SOC PAC

View full text Add to dashboard Cite

ABSTRACT. This has been the Year of the Baryon. Some low temperature ones were seen at high redshift, some high temperature ones were seen at low redshift, and some cooling ones were (probably) reheated. Astronomers saw the back of the Sun (which is also made of baryons), a possible solution to the problem of ejection of material by Type II supernovae (in which neutrinos push out baryons), the production of R Coronae Borealis stars (previously-owned baryons), and perhaps found the missing satellite galaxies (whose failing is that they have no baryons). A few questions were left unanswered for next year, and an attempt is made to discuss these as well.

show abstract

“…The analytical methods described above were used to compute the acoustic and magnetic (longitudinal + transverse + torsional) for stars with log g = 4 and different Teff (see Noble et al 2003a). The radiative losses were taken from Fawzy et al (2002c). The comparison clearly shows that there is a significant excess of the wave energy available for the acoustic heating (the acoustic fluxes should be compared only to the lower bound of the radiative losses) as well as for the magnetic heating (the magnetic fluxes should be higher than, or comparable to, the upper bound of the radiative losses) for stars with Teff ranging from 4000 K to 9000 K. Now, it remains to be determined whether these fluxes are sufficient to heat stellar chromospheres and transition regions.…”

Section: Wave Energy Available Versus Radiative Lossesmentioning

confidence: 99%

Heating of Stellar Chromospheres and Transition Regions

Musielak¹

2004

Symp. - Int. Astron. Union

View full text Add to dashboard Cite

Abstract.To explain the heating of stellar chromospheres and transition regions, two classes of heating mechanisms have been considered: dissipation of acoustic and magnetic waves generated in stellar convection zones; and dissipation of currents generated by photospheric motions of surface magnetic fields. The focus of this paper is on the wave heating mechanisms and on recent results which demonstrate that theoretical models of stellar chromospheres based on the wave heating can explain the "basal flux" and the observed Ca II emission in most stars but cannot account for the observed Mg II emission in active stars. The obtained results clearly show that the base of stellar chromospheres is heated by acoustic waves, the heating of the middle and upper chromospheric layers is dominated by magnetic waves associated with magnetic flux tubes, and that other non-wave heating mechanisms are required to explain the structure of the highest layers of stellar chromospheres and transition regions.

show abstract

Acoustic and magnetic wave heating in stars

Cited by 27 publications

References 41 publications

Dependence of coronal X-ray emission on spot-induced brightness variations in cool main sequence stars

Dependence of coronal X-ray emission on spot-induced brightness variations in cool main sequence stars

Astrophysics in 2002

Heating of Stellar Chromospheres and Transition Regions

Contact Info

Product

Resources

About