Photospheric Parameters Research Articles

Average Variations of Photospheric FeI and FeII Line Parameters as Function of the Magnetic Filling Factor

A series of 17 Fourier transform spectra taken at the McMath telescope near disk center in regions of different magnetic field strengths were analyzed. Applying a multi-variate regression analysis magnetic filling factors 0 < α ≥ 0.11 were determined. With α increasing from 0 to 0.11, line bisectors averaged over groups of lines of similar depth are found to show a blue shift decreasing from 0.35 km s–1 to nearly 0.1 km s–1, when referred to the MgI line λ5172.7å. The bisectors of FeII lines exhibit smaller blue shifts than FeI lines. The increase of bisector red shift near the continuum with increasing α, found earlier by Brandt and Solanki (1987), was confirmed and is tentatively interpreted as a manifestation of downdrafts in the vicinity of flux tubes (Deinzer et al., 1984).A significant increase of line width (typically between 3 and 8%, depending on line strength) and a decrease of line depth is found with increasing filling factor. For strong lines the equivalent width W shows no variation or a slight increase, while for the weaker lines a reduction of W between a few % and > 10% is found.

Atmospheric models for LBV’s at minimum and maximum states

We study the relation between photospheric and wind parameters of LBV’s on the basis of self-consistent atmospheric models. Our theoretical model consists of a spherically extended, dynamical NLTE atmosphere for the radiative transfer and a modified CAK code for the hydrodynamics. These codes are combined in an iterative scheme to achieve self-consistency.

X-ray Emission from Hot DA White Dwarfs; EXOSAT Results, and Implications for Atmospheric Models

AbstractWe present the observations of the photospheric X-ray spectra of hot DA white dwarfs, obtained with the 500 lines mm−1 Transmission Grating Spectrometer on EXOSAT. These spectra cover the full soft X-ray band, at high wavelength resolution and statistical quality. They allow us to do an accurate measurement of the photospheric parameters, particularly of effective temperature and chemical composition of the atmosphere.We consider the case of HZ 43 in some detail. Model atmospheric spectra that satisfy all measured absolute optical, UV and X-ray fluxes turn out not to fit the shape of the measured X-ray spectrum. However, from a comparison of model spectra calculated with different model atmospheres codes we infer the existence of a 15% systematic uncertainty in the model fluxes at the shortest wavelengths (λ < 100 Å) in current model calculations. This can explain the fitting problem. Since the systematic uncertainty in the models is larger than the statistical uncertainty in the shape of the measured X-ray spectrum of HZ 43, we cannot at present use this measured shape to derive the effective temperature and gravity. We revert to broad band photometry, using the measured integrated soft X-ray flux and the optical flux, to determine Te = 45,000 – 54,000K, R/R⊙ = 0.0140 – 0.0165. From the absence of the He II Ly edge at 227 Å in the measured spectrum, we set a upper limit on the photospheric helium abundance of He/H = 1.0 × 10−5; this upper limit is independent of the uncertainties in the model calculations mentioned above.

New measurements of photospheric magnetic fields in late-type stars and emerging trends

We report on recent results of our program to measure photospheric magnetic field strengths and filling factors from the analysis of unpolarized high spectral resolution and S/N line profiles. We have analyzed spectra obtained with the KPNO 4-m FTS, the MMT, and the McMath Reticon Spectrograph. With the latter instrument we now have an extensive data set through our synoptic and survey observing programs. Photospheric magnetic field parameters are obtained by comparison of observed and theoretical line profiles using an LTE code that includes line saturation and the full Zeeman pattern. We determine the nonmagnetic line broadening parameters for a star by fitting profiles of low Landé g lines formed under conditions similar to the high g lines which are used to infer magnetic fields. The effects of line blending are cancelled to first order by fitting profiles of the same high g lines in comparison inactive stars of the same spectral type. We have measured field parameters (outside of starspots) in dwarf stars of spectral type GO to dM3.5e (Ad Leo). We find a trend of increasing field strength with later spectral type, consistent with equal gas and magnetic pressure in the photosphere, and a trend of increasing filling factor with activity. Our data are inconsistent with the hypothesis of a constant number of magnetic flux tubes on active stars.

Global and Photospheric Physical Parameters of Active Dwarf Stars

AbstractPhysical parameters (temperature, luminosity, radius, mass and chemical abundance) of the photospheres of red dwarf flare stars and spotted stars are determined for quiescent conditions. The interrelations between these quantities are compared to the results of theoretical investigations for low mass stars. The evolutionary state of flare stars is discussed. Observational results from spectroscopic and photometric methods to determine the rotation of active dwarfs are reviewed. The possibilities of global oscillations in dwarf stars are considered and preliminary results of a photometric search for oscillation in red dwarf luminosities are presented.

On the Spectrum of the Herbig Be Star HD 200775

On the basis of high-dispersion spectra (I. Appenzeller, C. Bertout) and other observational material HD 200775 has been reanalyzed using ι Her as a comparison star. By comparing the depths in the wings of Hγ and Hδ and the equivalent widths of HeI-lines with predictions from model atmospheres we find for both stars Teff = 17000 ± 1000 k (in the scale of Kurucz' models, 1979) and log (g cm s−1) = 3.6 ± 0.3 corresponding to a spectral type of B3V. With a colorexcess EB-V = 0.56 and the standard interstellar reddening also the continuum energy distribution of HD 200775 corresponds to the above photospheric parameters if one allows for some circumstellar emission. However, the interstellar absorption features (4430 A and 2200 A) are of unusual weakness. The strength of the Hα emission requires either a nonthermal source of energy or a substantial rate of photo ionization from the level n = 2. We tend to conclude that for this second reason the dilution factor in the HII-region cannot be less than 10−2, a conclusion which is in accord with the finding that the radio emission at λ = 2 cm is less than 0.3 mJ which also indicates a very compact HII-region.

Solar luminosity variation. IV - The photospheric lines, 1976-1980

view Abstract Citations (51) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Solar luminosity variation. IV - The photospheric lines, 1976-1980 Livingston, W. ; Holweger, H. Abstract Kitt Peak full disk spectrophotometric records covering the period 1976-1980 have been analyzed to study the behavior of seven spectrum lines sensitive to photospheric parameters. A secular decrease of equivalent widths ranging from 0 to 2.3% is observed. From the lack of correlation with localized, short-lived features like sunspots and plages, it is concluded that the line weakenings are due to global variations of surface properties. Model atmosphere analysis suggests that the observed response pattern reflects a slight flattening of the lower photospheric temperature gradient, corresponding to a 15% increase in mixing length, at constant, effective temperature. The associated increase in the efficiency of convection can be reconciled with a constant luminosity if the change is assumed to occur only in the outer 100 km of the convection zone. Publication: The Astrophysical Journal Pub Date: January 1982 DOI: 10.1086/159564 Bibcode: 1982ApJ...252..375L Keywords: Line Spectra; Photosphere; Solar Flux; Solar Spectra; Stellar Luminosity; Stellar Spectrophotometry; Faculae; Secular Variations; Solar Activity Effects; Solar Atmosphere; Sunspots; Astrophysics full text sources ADS |

Analysis of spectra of α CMi and α Cen A observed with the orbiting stellar ultraviolet spectrophotometer S59 in ESRO's TD1A satellite

Ultraviolet spectra of α CMi and α Cen A taken with moderate spectral resolution (approx. 1.8 A) are used to analyse whether a determination of stellar chemical abundances of Fe and Cr and of the photospheric parameters is possible. For αCMi, for which good spectral data are available, we findTeff=7660±110 K; loggeff=3.05±0.1. Further, Δlogɛ(Fe)=−0.06±0.09; Δ log ɛ(Cr)=−0.01±0.09 with regard to ‘standard’ (solar) abundances. For α Cen A the resulting data — particularly the photospheric ones — are less certain, but it seems that the Fe abundance may be smaller than the ‘standard’ value.