scholarly journals Spectroscopy of Cool Stars from IUE Data

1988 ◽  
Vol 132 ◽  
pp. 163-168
Author(s):  
P. G. Judge
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
High Signal ◽  
Line Profiles ◽  
Signal To Noise ◽  
High Quality ◽  
Atmospheric Structure ◽  
General Properties ◽  
Cool Stars ◽  
The Impact

After nine years of operation the IUE satellite continues to provide valuable spectra of cool stars from 1200 to 3100 Å. The impact of these spectra has been greatest in studies of the outer regions of the atmospheres, above the photospheres, allowing the general properties of stellar chromospheres, transition regions and winds to be established. After outlining these properties, I focus on studies based on high signal–to–noise echelle spectra (λ/Δλ ∼1.2 ×104) of single stars, showing how high quality emission line profiles have been used to derive constraints on the outer atmospheric structure, which in turn have been used to examine models of heating and mass loss.

scholarly journals Photospheric molecular line profiles in cool stars

1981 ◽  
Vol 59 ◽  
pp. 119-124
Author(s):  
S.T. Ridgway ◽  
E.D. Friel
Keyword(s):  
Spectral Lines ◽  
High Spectral Resolution ◽  
High Signal ◽  
Line Profiles ◽  
Signal To Noise ◽  
Molecular Line ◽  
Ejection Process ◽  
Cool Stars ◽  
Mass Ejection ◽  
Selection Of

AbstractSpectral lines of the ΔV=2 rotation vibration bands of CO are well suited for study of photospheric motions and the mass ejection process in cool stars. We have obtained high spectral resolution (1.8 km/sec) and high signal-to-noise (>102) line profiles for a selection of K and M giants. These profiles are being studied for evidence of gas motions in the photosphere and near circumstellar regions.

Measurements of Differential Rotation in Cool Stars

2004 ◽  
Vol 215 ◽  
pp. 138-143 ◽  
Author(s):  
A. Reiners ◽  
J.H.M.M. Schmitt
Keyword(s):  
Differential Rotation ◽  
Rotation Parameter ◽  
High Signal ◽  
Body Rotation ◽  
Signal To Noise ◽  
Transform Method ◽  
Solid Body Rotation ◽  
Cool Stars ◽  
Show Evidence ◽  
The Fourier Transform

We have obtained high resolution (R ≈ 220000) - high signal-to-noise (S/N > 500) spectra of 142 field dwarfs of spectral types F–K and v sin i ≤ 45 km s–1. Using the Fourier Transform Method (FTM) we precisely determined rotational velocities (Δ v sin i < 1.0 km s–1). For stars with v sin i ≥ 12.0 km s–1 this method allows the detection of deviations from solid body rotation. In the case of symmetric profiles the differential rotation parameter α = (ωequator – ωpole) / ωequator can be determined. This was possible for 32 of our sample stars; ten stars show evidence for solar-like differential rotation with α > 0.0. Thus it becomes possible to search for connections between differential rotation, rotational velocities and other stellar parameters. Signatures of differential rotation could be found on stars rotating as fast as v sin i = 42 km s–1. Particularly the Li-depleted stars turned out to show strong signatures of differential rotation. Our measurements support the idea, that Li-depletion in fast rotators (v sin i > 15 km s–1) is closely connected to differential rotation.

scholarly journals Simultaneous Spectroscopy and Polarimetry of Be Stars

1987 ◽  
Vol 92 ◽  
pp. 84-86
Author(s):  
D. R. Gies ◽  
David McDavid
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
Absorption Line ◽  
Line Profile ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Line Profiles ◽  
Initial Attempt ◽  
Rapid Variability ◽  
Hα Emission

Evidence is now accumulating that many Be stars display photospheric line profile variations on timescales of days or less that are probably caused by nonradial pulsations (Baade 1984; Penrod 1986). In some circumstances these pulsations can promote mass loss into the circumstellar envelope, and consequently the conditions in the inner part of the envelope may vary on similar timescales. Changes in the envelope could produce variations in the polarization and emission line profiles, and observers have reported rapid variability in both. We describe here an initial attempt to search for simultaneous variations in continuum polarization, Hα emission, and the He I λ6678 photospheric absorption line in order to investigate correlated changes on short timescales.

scholarly journals The 12C/13C Ratio in Unevolved Cool Stars

1988 ◽  
Vol 132 ◽  
pp. 589-592
Author(s):  
Y. Chmielewski ◽  
D. L. Lambert
Keyword(s):  
High Resolution ◽  
Preliminary Analysis ◽  
Isotope Ratio ◽  
Signal To Noise Ratio ◽  
Carbon Isotope Ratio ◽  
High Signal ◽  
Reasonable Accuracy ◽  
Signal To Noise ◽  
Dwarf Stars ◽  
Cool Stars

We show that the carbon isotope ratio 12C/13C in the atmosphere of dwarf stars can be determined with reasonable accuracy from high resolution, high signal-to-noise ratio observations of the CH G-band in their spectra. Lines suitable for this purpose are selected from consideration of the solar case, for which 12C/13C = 89 is derived. A preliminary analysis of these features in the spectra of μ Her, δ Eri and τ Cet yields 12C/13C values of 84, 80 and 150 respectively.

scholarly journals The first Doppler imaging of the active binary prototype RS Canum Venaticorum

2020 ◽  
Vol 492 (3) ◽  
pp. 3647-3656 ◽  
Author(s):  
Yue Xiang ◽  
Shenghong Gu ◽  
U Wolter ◽  
J H M M Schmitt ◽  
A Collier Cameron ◽  
...  
Keyword(s):  
High Resolution ◽  
Differential Rotation ◽  
Binary Star ◽  
Doppler Imaging ◽  
High Signal ◽  
Line Profiles ◽  
Signal To Noise ◽  
Spot Pattern ◽  
Deconvolution Technique ◽  
Modelling Studies

ABSTRACT We present the first Doppler images of the prototypical active binary star RS Canum Venaticorum, derived from high-resolution spectra observed in 2004, 2016 and 2017, using three different telescopes and observing sites. We apply the least-squares deconvolution technique to all observed spectra to obtain high signal-to-noise line profiles, which are used to derive the surface images of the active K-type component. Our images show a complex spot pattern on the K star, distributed widely in longitude. All star-spots revealed by our Doppler images are located below a latitude of about 70°. In accordance with previous light-curve modelling studies, we find no indication of a polar spot on the K star. Using Doppler images derived from two consecutive rotational cycles, we estimate a surface differential rotation rate of ΔΩ = −0.039 ± 0.003 rad d−1 and α = ΔΩ/Ωeq = −0.030 ± 0.002 for the K star. Given the limited phase coverage during those two rotations, the uncertainty of our differential rotation estimate is presumably higher.

scholarly journals What is the essential physics of mass loss from late-type stars?

1987 ◽  
Vol 122 ◽  
pp. 271-287
Author(s):  
Jeffrey L. Linsky
Keyword(s):  
Mass Loss ◽  
Solar Atmosphere ◽  
Critical Role ◽  
Large Mass ◽  
Late Type ◽  
Atmospheric Structure ◽  
Cool Stars ◽  
Thermally Driven ◽  
Molecular Condensation ◽  
Loss Rates

In this review I consider what clues the data are providing us concerning the mass loss from late-type stars. I consider in turn the major classes of mass-loss mechanisms (thermally-driven winds, radiatively-driven winds, and wave-driven winds), and consider whether the empirical mass loss rates and other data are consistent with any of these mechanisms acting alone. It is likely that several mechanisms act together to produce the large mass loss rates in the Mira and non-pulsating M supergiants. Studies of the solar atmosphere suggest that thermal bifurcation driven by molecular condensation instabilities may play a critical role in cooling the atmospheres of luminous cool stars and forming silicate dust. It is possible that several metastable modes of atmospheric structure may exist for a given set of stellar parameters.

scholarly journals Doppler Imaging of Starspots

1983 ◽  
Vol 71 ◽  
pp. 379-385
Author(s):  
Steven S. Vogt ◽  
G. Donald Penrod
Keyword(s):  
Doppler Imaging ◽  
Stellar Disk ◽  
Doppler Velocity ◽  
High Signal ◽  
Line Profiles ◽  
Signal To Noise ◽  
Rs Cvn Stars ◽  
Spot Model ◽  
Very High ◽  
General Appearance

ABSTRACTWe discuss a newly-developed technique for spatially resolving starspots on some of the more rapidly rotating RS CVn stars. Basically, the method uses high resolution, very high signal-to-noise spectral line profiles and exploits the Doppler velocity correspondence between position across the stellar disk and wavelength position across a rotationally broadened line profile to synthesize an image of the star, showing the location, sizes, and shapes of its starspots. Though still in a developmental stage, the technique is already yielding information about the structure and general appearance of starspots. Examples of Doppler Imaging observations of HR 1099 will be presented, along with a movie showing the behavior of synthetic line profiles generated from a computer spot model.

scholarly journals Lithium Abundances of Solar-Type Stars: A Critical Application of High Signal-to-Noise, High Resolution Spectroscopy

1988 ◽  
Vol 132 ◽  
pp. 381-386
Author(s):  
David R. Soderblom
Keyword(s):  
High Resolution ◽  
The State ◽  
High Resolution Spectroscopy ◽  
High Signal ◽  
Signal To Noise ◽  
High Quality ◽  
Essential Properties ◽  
Solar Type ◽  
Lithium Depletion

The study of lithium depletion in solar-type stars should help elucidate essential properties of convection in those objects. Recent high-quality observations have revealed extensive flaws in our understanding of this phenomenon. The state of our knowledge of Li depletion is reviewed, with a brief possible explanation of it all.

The importance of non-photon noise in astronomical spectropolarimetry

2014 ◽  
Vol 10 (S305) ◽  
pp. 181-185
Author(s):  
S. Bagnulo ◽  
L. Fossati ◽  
J. D. Landstreet ◽  
O. Kochukhov
Keyword(s):  
Data Reduction ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Instrumental Effects ◽  
Signal To Noise ◽  
Photon Noise ◽  
Stellar Magnetic Fields ◽  
The Impact ◽  
Spurious Signals ◽  
Small Instrument

AbstractStellar spectropolarimetry has become an extremely popular technique during the last decade or two, and has led to major advances in the studies of stellar magnetic fields. Many important discoveries have been made thanks to ultra-precise measurements of very small polarimetric signals, which require very stable instruments and special observing strategies. The so called beam-swapping technique is a well-known polarimetric technique capable of suppressing many spurious signals due to various instrumental effects. However, when one is interested in ultra-high signal-to-noise ratio measurements, observers start to hit various limitations introduced by the instrument, by the atmosphere, and even by the software for data-reduction. These limitations cannot be overcome by the observing strategies, and sources of errors other than photon-noise must be taken into account. Here we discuss the advantages of the beam-swapping technique, and the impact of small instrument and atmospheric instabilities, and how these issues offer an explanation for the origin of the apparently significant observed polarisation signals produced by effects other than those intrinsic to the observed target.

scholarly journals Effective Temperatures and Gravities for O-Type Stars Determined from High Precision Line Profiles and Wind-Blanketed Model Atmospheres

1988 ◽  
Vol 132 ◽  
pp. 127-130 ◽  
Author(s):  
B. Bohannan ◽  
S. A. Voels ◽  
D. C. Abbott ◽  
D. G. Hummer
Keyword(s):  
Spectral Type ◽  
Massive Stars ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Line Profiles ◽  
Astronomical Instrumentation ◽  
Signal To Noise ◽  
Effective Temperatures ◽  
Stellar Properties

Analysis of line profiles obtained with astronomical instrumentation capable of high signal-to-noise ratio spectroscopy have contributed significant new precision to the determination of the basic stellar parameters of hot, luminous, mass-loosing stars. Accurate measurement of such stellar properties as effective temperature and helium abundance for stars of spectral type O and early B is important not only to the physics of these stars but also to the environment in which they are located. The overall goals of the work we summarize here are to refine the spectral-type vs. temperature calibration for the most massive stars and to determine helium abundances for stars that are loosing mass at a rate sufficiently high to affect their evolution. Details of our procedures are described in the analysis of ξ Puppis by Bohannan et al. (1986).

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