Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 0801.3898

Chromospheric features of LQ Hydrae from H-alpha line profiles

A. Frasca·Zs. Kovari·K. G. Strassmeier·K. Biazzo
View original source ↗Read source document ↗Export metadata ↓

Abstract

We analyze the H-alpha spectral variability of the rapidly-rotating K1-dwarf LQ Hya using high-resolution H-alpha spectra recorded during April-May 2000. Chromospheric parameters were computed from the H-alpha profile as a function of rotational phase. We find that all these parameters vary in phase, with a higher chromospheric electron density coinciding with the maximum H-alpha emission. We find a clear rotational modulation of the H-alpha emission that is better emphasized by subtracting a reference photospheric template built up with a spectrum of a non-active star of the same spectral type. A geometrical plage model applied to the H-alpha variation curve allows us to derive the location of the active regions that come out to be close in longitude to the most pronounced photospheric spots found with Doppler imaging applied to the photospheric lines in the same spectra. Our analysis suggests that the H-alpha features observed in LQ Hya in 2000 are a scaled-up version of the solar plages as regards dimensions and/or flux contrast. No clear indication of chromospheric mass motions emerges.

Explore related subjects

astro-ph

Keep this discovery

BibTeXRIS

A. Frasca, Zs. Kovari, K. G. Strassmeier, K. Biazzo. 2008-01-25. Chromospheric features of LQ Hydrae from H-alpha line profiles. https://doi.org/10.1051/0004-6361:20079058

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2009

Numerical Simulation of the Viscous-like Flow in and Around the Plasma Tail of a Comet

We model the interaction of the solar wind with the plasma tail of a comet by means of numerical simulations, taking into account the effects of viscous-like forces.A 2D hydrodynamical, two species, finite difference code has been developed for the solution of the time dependent continuity, momentum and energy conservation equations, as applied to the problem at hand. Velocity, density and temperature profiles across the tail are obtained. Several cases with different flow parameters are considered in order to study the relative importance of viscous-like effects and the coupling between species on the flow dynamics. Assuming a Mach number equal to 2 for the incident solar wind as it flows past the comet nucleus, the flow exhibits three transitions with location and properties depending on the Reynolds number for each species and on the ratio of the timescale for inter-species coupling to the crossing time of the free flowing solar wind. By comparing our results with the measurements taken in situ by the Giotto spacecraft during its flyby of comet Halley we constrain the flow parameters for both plasmas. In the context of our approximations, we find that our model is qualitatively consistent with the in situ measurements as long as the Reynolds number of the solar wind protons and of cometary H2O+ ions is low, less than 100, suggesting that viscous-like momentum transport processes may play an important role in the interaction of the solar wind and the plasma environment of comets.

astro-ph↗
arXiv2009

Mass and Redshift Dependence of Dark Halo Structure

Using a combination of N-body simulations with different resolutions, we study in detail how the concentrations of cold dark matter (CDM) halos depend on halo mass at different redshifts. We confirm that halo concentrations at the present time depend strongly on halo mass, but our results also show marked differences from the predictions of some early empirical models. Our main result is that the mass dependence of the concentrations becomes weaker at higher redshifts, and at z >~ 3 halos of mass greater than 10^{11} Msun/h all have a similar median concentration, c ~ 3.5. While the median concentrations of low-mass halos grow significantly with time, those of massive halos change only little with redshifts. These results are quantitatively in good agreement with the empirical model proposed by Zhao et al. which shows that halos in the early fast accretion phase all have similar concentrations.

astro-ph↗
arXiv2009

Cosmology from very high energy $γ$-rays

In this work we study how the cosmological parameter, the Hubble constant $H_0$, can be constrained by observation of very high energy (VHE) $γ$-rays at the TeV scale. The VHE $γ$-rays experience attenuation by background radiation field through $e^+e^-$ pair production during the propagation in the intergalactic space. This effect is proportional to the distance that the VHE $γ$-rays go through. Therefore the absorption of TeV $γ$-rays can be taken as cosmological distance indicator to constrain the cosmological parameters. Two blazars Mrk 501 and 1ES 1101-232, which have relatively good spectra measurements by the atmospheric Cerenkov telescope, are studied to constrain $H_0$. The mechanism constraining the Hubble constant adopted here is very different from the previous methods such as the observations of type Ia supernovae and the cosmic microwave background. However, at $2σ$ level, our result is consistent with other methods.

astro-ph↗