scholarly journals High S/N Na I D Line Profiles in Late-Type MS Stars and their Importance for Stellar Modelling

1993 ◽  
Vol 137 ◽  
pp. 190-192 ◽  
Author(s):  
E. Covino ◽  
M.T. Gomez ◽  
G. Severino ◽  
M. Franchini
Keyword(s):  
High Resolution ◽  
Synthesis Method ◽  
Atomic Data ◽  
Line Profiles ◽  
Late Type ◽  
Stellar Spectrum ◽  
Dwarf Stars ◽  
Observational Techniques ◽  
Numerical Fit

Progress in observational techniques (i.e. high S/N spectroscopy) and modelling (e.g. RE models including convection, nonLTE codes, accurate atomic data) make significant to carry to extremes the numerical fit of a portion of the stellar spectrum and try to interpret the residual differences between calculations and observations in terms of stellar characteristics new respect to the employed model.We have started to apply this synthesis method to a set of high resolution, high S/N spectra of late-type dwarfs in the region of the Na I D lines, obtained at ESO with the 1.4m CAT on May 1989 (Franchini et al. 1992). The dwarf stars are modelled in radiative equilibrium (RE), and the Na I D line synthesis accounts for nonLTE and blend effects.

scholarly journals Lithium Abundance in Late-Type Stars

2000 ◽  
Vol 198 ◽  
pp. 368-369
Author(s):  
L Pompéia ◽  
B Barbuy ◽  
M. Grenon
Keyword(s):  
High Resolution ◽  
Radial Velocity ◽  
Detailed Analysis ◽  
Absolute Magnitude ◽  
Late Type ◽  
Lithium Abundance ◽  
Dwarf Stars ◽  
The Absolute

We have a list of nearby bulge-like turnoff stars with metallicities in the range −0.3 ≤ [Fe/H] ≤ +0.6, for which we have the absolute magnitude from Hipparcos, Geneva photometry (therefore temperature and metallicity), and radial velocity from Coravel (Grenon 1990, 1997). From Hipparcos data, the turnoff of these field stars indicate an age of 10-11 Gyr, which would be the age of the most metal-rich component of the bulge.We obtained high resolution échelle spectra with FEROS, with the aim to carry out detailed analysis of these stars. In this paper we present the Li abundance for 40 of these metal-rich and old dwarf stars, as a function of their temperatures.

scholarly journals Chromospheres and Winds of Cool Stars

1992 ◽  
Vol 9 ◽  
pp. 477-479
Author(s):  
Kenneth G. Carpenter
Keyword(s):  
High Resolution ◽  
Complex Shape ◽  
The Self ◽  
Line Profiles ◽  
Late Type ◽  
Hybrid Star ◽  
Star Models ◽  
Cool Stars ◽  
Type Giant ◽  
Early Operations

I present data acquired during the early operations era of the HST with the Goddard High Resolution Spectrograph (GHRS) on three late-type giant and supergiant stars: α Tau (K5 III non-coronal), λ Dra (K5 III hybrid), and α Ori (M2 lab). Figure 1 shows fits to echelle (R=100,000) line profiles of three ions seen in the spectrum of α Tau. The Co II line can be fit with a single gaussian, the self-reversed Fe II line with a combination of an emission and absorption gaussian, but the unreversed C II lines require two emission gaussians of substantially different FWHM and maxima. The complex shape of the C II profiles suggests that the turbulent velocity distribution in the chromosphere is anisotropic (e.g. Gray 1988) or that the lines are formed in two regions characterized by significantly different Teff and Vturb, as in the hybrid star models of Harper (1991).

scholarly journals Rotation periods of late-type dwarf stars from time series high-resolution spectroscopy of chromospheric indicators

2015 ◽  
Vol 452 (3) ◽  
pp. 2745-2756 ◽  
Author(s):  
A. Suárez Mascareño ◽  
R. Rebolo ◽  
J. I. González Hernández ◽  
M. Esposito
Keyword(s):  
Time Series ◽  
High Resolution ◽  
High Resolution Spectroscopy ◽  
Late Type ◽  
Dwarf Stars ◽  
Rotation Periods

scholarly journals Inferring Mass Loss Rates for Cool Luminous Stars from High-Resolution GHRS Spectra

2000 ◽  
Vol 177 ◽  
pp. 303-312
Author(s):  
J. L. Linsky ◽  
G. M. Harper ◽  
J. Valenti ◽  
P. D. Bennett ◽  
A. Brown
Keyword(s):  
High Resolution ◽  
Radiative Transfer ◽  
Mass Loss ◽  
Spherically Symmetric ◽  
Density Structure ◽  
Line Profiles ◽  
Late Type ◽  
Partial Redistribution ◽  
Ionization Structure ◽  
Symmetric Geometry

We discuss GHRS spectra of single and binary late-type stars and describe in detail the spectra of α TrA and of ζ Aurigae obtained at ten orbital phases. The wind properties of α TrA are derived using a complete redistribution radiative transfer code, and we describe the properties of a new code, PRISMA, that we are building to fit line profiles using partial redistribution in a spherically-symmetric geometry. The ζ Aur spectra show that the mass loss process is variable on the timescale of several months, the wind density structure does not repeat from orbit to orbit, and the wind ionization structure is complex.

scholarly journals Analysis of High Resolution Stellar Line Profiles

1980 ◽  
Vol 51 ◽  
pp. 75-84
Author(s):  
David F. Gray
Keyword(s):  
High Resolution ◽  
Spectral Line ◽  
Spectral Resolution ◽  
Signal To Noise Ratio ◽  
Physical Phenomenon ◽  
Velocity Fields ◽  
Line Profiles ◽  
Late Type ◽  
Signal To Noise ◽  
Line Shapes

High resolution implies that we obtain some information on spectral line shapes. In late-type stars, we need to measure velocities of a few km/sec to accomplish this. Increasing the spectral resolution and the signal to noise ratio allows us to progress step by step toward deeper physical understanding. The steps we take often lead to good debate and “stimulate” our lives. I am sometimes amused at the urgency we feel to press on to the next step. We rarely seem to pause and enjoy the completion of previous steps. Perhaps this is because we always see shortcomings in completed work. Quite typically one will “discover” the importance of some physical phenomenon (It makes little difference how many others already know about it.), and in his eyes everything done previously becomes wrong because this phenomenon was not included. We used to hear how Milne-Eddington or Schuster-Schwarzschild model atmospheres were inadequate -we had to use instead properly computed depth dependence. We used to hear how LTE models were no good - we had to use more detailed physics. Now we talk about line analyses being inadequate because it has not included velocity fields. The curious thing is that we believe that including our pet phenomenon gives the correct models. We ignore all those other phenomena as yet unseen! (Is this a mechanism for maintaining sanity?) I think it really amounts to a statement of what we are able to measure, compute, or understand.

X‐Ray Spectroscopy of Rapidly Rotating, Late‐Type Dwarf Stars

1999 ◽  
Vol 512 (2) ◽  
pp. 874-891 ◽  
Author(s):  
K. P. Singh ◽  
S. A. Drake ◽  
E. V. Gotthelf ◽  
N. E. White
Keyword(s):  
Late Type ◽  
Dwarf Stars ◽  
X Ray

scholarly journals The Time Dependence of the Phases of the Harmonics Relative to the 1490 sec Fundamental in PG1346+082

1989 ◽  
Vol 114 ◽  
pp. 296-299
Author(s):  
J. L. Provencal ◽  
J. C. Clemens ◽  
G. Henry ◽  
B. P. Hine ◽  
R. E. Nather ◽  
...  
Keyword(s):  
White Dwarf ◽  
Compact Object ◽  
Detailed Knowledge ◽  
Line Profiles ◽  
Pressure Broadening ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Adequate Understanding ◽  
Magnitude Variation ◽  
Hydrogen Lines

White dwarf stars provide important boundary conditions for the understanding of stellar evolution. An adequate understanding of even these simple stars is impossible without detailed knowledge of their interiors. PG1346+082, an interacting binary white dwarf system, provides a unique opportunity to view the interior of one degenerate as it is brought to light in the accretion disk of the second star as the primary strips material from its less massive companion (see Wood et at. 1987).PG1346+082 is a photometric variable with a four magnitude variation over a four to five day quasi-period. A fast Fourier transform (FFT) of the light curve shows a complex, time-dependent structure of harmonics. PG1346+082 exhibits flickering – the signature of mass transfer. The optical spectra of the system contain weak emission features during minimum and broad absorption at all other times. This could be attributed to pressure broadening in the atmosphere of a compact object, or to a combination of pressure broadening and doppler broadening in a disk surrounding the compact accretor. No hydrogen lines are observed and the spectra are dominated by neutral helium. The spectra also display variable asymmetric line profiles.

New line profiles of sodium and potassium perturbed by helium for brown dwarf and very cool white dwarf stars

2008 ◽  
Author(s):  
M. Christova ◽  
N. F. Allard ◽  
J. F. Kielkopf ◽  
D. Homeier ◽  
F. Allard ◽  
...  
Keyword(s):  
White Dwarf ◽  
Line Profiles ◽  
Brown Dwarf ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Sodium And Potassium
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