Person:
Fernández Figueroa, María José

First Name

María José

Last Name

Fernández Figueroa

URI

https://hdl.handle.net/20.500.14352/83017

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Area

Astronomía y Astrofísica

Identifiers

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Now showing 1 - 10 of 12

Uvbyβ photometry of active-chromosphere binaries .1. The system TZ Coronae Borealis
(Astronomical journal, 1986) Giménez, A.; Ballester, J. L.; Reglero, V.; Fernández Figueroa, María José; Castro Rubio, Elisa de
Simultaneous uvby and Hβ photometry of thee noneclipsing double-lined spectroscopic binary TZ CrB, an active binary system with almost unevolved components, is presented. A small amplitude distortion wave (0.012 mag in y) has been found with maximum light at phase ∽0.75. No variations in color or the βindex during the orbital cycle have been detected within the precision of the observations. The resulting color indices in the standard uvby system allow the estimation of some basic stellar parameters, such as the average effective temperature ∽6000 K and the stellar radii of the component stars ∽1.1 R_⨀. These results, together with available spectroscopic data, permit a consistent picture for this interesting binary to be obtained.
General properties of RS CVn systems
(Monthly notices of the Royal Astronomical Society, 1988) Montesinos, B.; Giménez, A.; Fernández Figueroa, María José
In this work we analyse the behaviour of 22 members of the RS CVn family whose absolute parameters are known by observation. We have carried out a study in comparison with detached and normal-evolution systems in order to obtain some general properties of this group of active binaries and test the evolutionary status. A comparison with evolutionary tracks of several metallicities and helium contents shows that there is a trend in these stars to have metal abundances equal to or larger than the solar one. The results are discussed in the light of the peculiar characteristics of this kind of binaries .
Emissions from the transition regions and coronae of three cool dwarf stars
(Astronomy & Astrophysics, 1983) Fernández Figueroa, María José; Castro Rubio, Elisa de; Rego Fernández, Manuel
Ultraviolet emissions of τCet, δPav, and 61 Cyg A have been analysed to determine the structure of their outer atmospheres. Emission line fluxes are used to find the emission measure distributions. Using two boundary values of the electron pressure, models of the transition region have been derived. In the two models of τCet the net conductive flux is less than the radiation losses at all temperatures. However, for δPav and 61 Cyg A the model with the upper boundary value of the electron pressure has a temperature range where the radiative losses are less than the net conductive fluxes. Measured X-ray fluxes are used to test the coronal temperature values derived from the ultraviolet observations.
The relationship between soft X-rays and the 1640 Å feature fluxes in late-type stars
(Astronomy and astrophysics, 1983) Rego Fernández, Manuel; González Riestra, R.; Fernández Figueroa, María José
The λ 1640 feature has been observed in a sample of late type stars of different luminosity classes. The intensity was measured from IUE low dispersion spectra, and it has been compared with the observed X-ray fluxes, finding a relationship between both quantities for "solar type" stars. The X-ray fluxes derived from this relationship for a reduced sample of stars are consistent with the observed ones in the case of "solar type" stars. "Non solar type" stars exhibit discrepancies that could be explained assuming that the λ 1640 feature is formed by contributers other than He II, which supply an important fraction of this emission in "solar type" stars. The obtained empirical relationship has been used to derive the X-ray flux for some stars that have not been observed in the X-ray range.
Evidence of the connection between internal magnetic fields and chromospheric activity in late-type stars
(Monthly notices of the Royal Astronomical Society, 1987) Montesinos, B.; Fernández Figueroa, María José; Castro Rubio, Elisa de
In this work we try to establish a connection between the dynamo effect, which operates in the convection zone of late-type stars, and the chromospheric activity observed in these objects. We estímate in a theoretical way, for a sample of main-sequence active stars with spectral types G and K, the magnetic field generated in a region close to the base of the convection zone and the filling factor (fraction of stellar surface covered by strong magnetic fields). The analysis of the behaviour both of the filling factor and the activity indicator R(CaII + MgII) against several stellar parameters ( B-V and the Rossby number) supports the existence of a link between the interior processes and the surface activity.
Analysis of Ca II emission lines in seven RSCVn systems
(Astronomy & Astrophysics, 1986) Fernández Figueroa, María José; Montesinos, B.; Castro Rubio, Elisa de; Rego Fernández, Manuel; Giménez, A.; Reglero, V.
We report here new Ca II H and K emission line fluxes and equivalent widths for seven RSCVn binary systems, observed at several orbital phases. All the stars show enhanced chromospheric activity. With information from available spectra, an in dividual study for each star has been done. Double emission has been found for some systems in which perhaps the hotter component could be the more active. We have tested spectroscopically the model of localized active regions for the prototype RSCVn.
The transition region structure of κ ceti
(Astronomy and astrophysics, 1981) Fernández Figueroa, María José; Castro Rubio, Elisa de; Rego Fernández, Manuel
Observations of κ Ceti (HD 20630), G5 V, obtained with the IUE satellite have been analysed to determine the structure of its outer atmosphere. This analysis is used to derive a model of transition region and to examine the terms of energy balance equation.
Hβ photometry for UVBY standard stars
(Astronomical journal, 1988) Reglero, V.; Giménez, A.; Fabregat, J.; de Catro, E.; Fernández Figueroa, María José; De Castro, A.
From 1984 to 1986 the authors made several observational campaigns at Calar Alto and La Palma Observatories using the uvby and β photometric systems to monitor a selected sample of late-type variable stars. In this paper they present the β values for 38 uvby standard stars to contribute to the uvby-β calibration works on late-type stars. In the final discussion, the β computed values are plotted against the Stroemgren b-y, m_(1), and c_(1) indices.
The Mg II emission in a sample of regular-period RS CVn systems
(Astronomy & Astrophysics, 1986) Fernández Figueroa, María José; Sedano, J. L.; Castro Rubio, Elisa de
We have studied a sample of ten RS CVn systems by means of IUE high resolution long wavelength spectra. A general trend toward decreasing chromospheric activity (R_hk) for slower rotating stars has been found. Considering the R_hk values and their relation with structural parameters (T_eff, logg, log P_rot) we suggest that there are two possible different activity levels. The less active systems have Rhk chromospheric activity levels similar to the single cool stars showing the same general trend. A relation between R_hk and the inverse Rossby number has been obtained, in which the RS CVn stars fill the gap found by Rucinski between W UMa and the main-sequence stars.
Analysis of the far ultraviolet silicon lines in G dwarf stars
(Astronomy and astrophysics, 1980) Fernández Figueroa, María José; Rego Fernández, Manuel; Cornide Castro-Piñeiro, Manuel
The structure of the outer stellar regions is investigated for four G type dwarfs observed with the IUE satellite. Line fluxes of the Si II lines at 1817 Å, 1808 A, and 1309 Å and Si III at 1206 Å are used to obtain temperatures and electronic densities. A temperature of 16,000 K is found from the lines at 1817 Å and 1808 Å, 26,000 K from the 1309 A line and 50,000 K from that at 1206 A. Predicted fluxes are compared with the observed ones. The significance of the results is discussed in terms of line formation regions.