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.

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.

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 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 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.

Sun-as-a-star observations of the 2017 August 21 solar eclipse

2019 ◽  
Vol 15 (S354) ◽  
pp. 473-480
Author(s):  
Ekaterina Dineva ◽  
Carsten Denker ◽  
Meetu Verma ◽  
Klaus G. Strassmeier ◽  
Ilya Ilyin ◽  
...  
Keyword(s):  
Solar Eclipse ◽  
Spectral Resolution ◽  
Solar Disk ◽  
State Of The Art ◽  
Active Regions ◽  
Spectral Lines ◽  
High Spectral Resolution ◽  
Line Profiles ◽  
Stellar Spectra ◽  
Limb Darkening

AbstractThe Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) is a state-of-the-art, thermally stabilized, fiber-fed, high-resolution spectrograph for the Large Binocular Telescope (LBT) at Mt. Graham, Arizona. During daytime the instrument is fed with sunlight from the 10-millimeter aperture, fully automated, binocular Solar Disk-Integrated (SDI) telescope. The observed Sun-as-a-star spectra contain a multitude of photospheric and chromospheric spectral lines in the wavelength ranges 4200–4800 Å and 5300–6300 Å. One of the advantages of PEPSI is that solar spectra are recorded in the exactly same manner as nighttime targets. Thus, solar and stellar spectra can be directly compared. PEPSI/SDI recorded 116 Sun-as-a-star spectra during the 2017 August 21 solar eclipse. The observed maximum obscuration was 61.6%. The spectra were taken with a spectral resolution of ≈ 250000 and an exposure time of 0.3 s. The high-spectral resolution facilitates detecting subtle changes in the spectra while the Moon passes the solar disk. Sun-as-a-star spectra are affected by changing contributions due to limb darkening and solar differential rotation, and to a lesser extend by supergranular velocity pattern and the presence of active regions on the solar surface. The goal of this study is to investigate the temporal evolution of the chromospheric Na D doublet during the eclipse and to compare observations with synthetic line profiles computed with the state-of-the-art Bifrost code.

scholarly journals The Galactic Evolution of Beryllium

2000 ◽  
Vol 198 ◽  
pp. 389-396 ◽  
Author(s):  
Ann Merchant Boesgaard
Keyword(s):  
Chemical Evolution ◽  
Cosmic Ray ◽  
High Spectral Resolution ◽  
High Signal ◽  
Galactic Chemical Evolution ◽  
Ray Theory ◽  
Signal To Noise ◽  
Metal Abundances ◽  
Cosmology Observations ◽  
The Relationship

The abundance of beryllium has been determined in unevolved stars over a range metal abundances in order to enhance our understanding of the chemical evolution of our Galaxy, cosmic-ray theory, and cosmology. Observations of 27 stars have been made with Keck I with HIRES at high spectral resolution (45,000) and high signal-to-noise ratios (60 - 110 typically). We find a remarkably linear relationship between log N(Be/H) and [Fe/H] with a slope of 0.96 (±0.04). Similarly, the relationship between log N(Be/H) and [O/H] is linear with a slope of 1.45 (±0.04). Beryllium increases at the same rate as Fe, but much faster than O. This provides constraints for and insights into models of Galactic chemical evolution. There is some evidence for an intrinsic spread in Be at a given [O/H] or [Fe/H]. There is no evidence of a plateau in Be at the lowest metallicities down to log N(Be/H) = —13.5.

scholarly journals [C II] 158 μm self-absorption and optical depth effects

2020 ◽  
Vol 636 ◽  
pp. A16 ◽  
Author(s):  
C. Guevara ◽  
J. Stutzki ◽  
V. Ossenkopf-Okada ◽  
R. Simon ◽  
J. P. Pérez-Beaupuits ◽  
...  
Keyword(s):  
Optical Depth ◽  
Column Density ◽  
Signal To Noise Ratio ◽  
Far Infrared ◽  
Emission Lines ◽  
High Spectral Resolution ◽  
Line Of Sight ◽  
High Signal ◽  
Line Profiles ◽  
Star Forming

Context. The [C II] 158 μm far-infrared fine-structure line is one of the most important cooling lines of the star-forming interstellar medium (ISM). It is used as a tracer of star formation efficiency in external galaxies and to study feedback effects in parental clouds. High spectral resolution observations have shown complex structures in the line profiles of the [C II] emission. Aims. Our aim is to determine whether the complex profiles observed in [12C II] are due to individual velocity components along the line-of-sight or to self-absorption based on a comparison of the [12C II] and isotopic [13C II] line profiles. Methods. Deep integrations with the SOFIA/upGREAT 7-pixel array receiver in the sources of M43, Horsehead PDR, Monoceros R2, and M17 SW allow for the detection of optically thin [13C II] emission lines, along with the [12C II] emission lines, with a high signal-to-noise ratio. We first derived the [12C II] optical depth and the [C II] column density from a single component model. However, the complex line profiles observed require a double layer model with an emitting background and an absorbing foreground. A multi-component velocity fit allows us to derive the physical conditions of the [C II] gas: column density and excitation temperature. Results. We find moderate to high [12C II] optical depths in all four sources and self-absorption of [12C II] in Mon R2 and M17 SW. The high column density of the warm background emission corresponds to an equivalent Av of up to 41 mag. The foreground absorption requires substantial column densities of cold and dense [C II] gas, with an equivalent Av ranging up to about 13 mag. Conclusions. The column density of the warm background material requires multiple photon-dominated region surfaces stacked along the line of sight and in velocity. The substantial column density of dense and cold foreground [C II] gas detected in absorption cannot be explained with any known scenario and we can only speculate on its origins.

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).

scholarly journals A High Resolution XUV Grating Monochromator for the Spectral Selection of Ultrashort Harmonic Pulses

2019 ◽  
Vol 9 (12) ◽  
pp. 2502
Author(s):  
Nicola Fabris ◽  
Paolo Miotti ◽  
Fabio Frassetto ◽  
Luca Poletto
Keyword(s):  
Extreme Ultraviolet ◽  
Spectral Lines ◽  
Resolving Power ◽  
High Spectral Resolution ◽  
Test Case ◽  
Optical Elements ◽  
Broad Energy Range ◽  
Grating Monochromator ◽  
Set Up ◽  
Selection Of

A new monochromator with high spectral resolution in the extreme ultraviolet (XUV) has been developed for high-order laser harmonics selection. The system has three optical elements—a cylindrical (or spherical) focusing mirror, a uniform-line-spaced plane grating, and a plane mirror. The last element is required to maintain the focus on a fixed vertical slit when the grating subtended angle is changed in order to minimize the spectral defocusing aberration. The parameters of the focusing mirror are determined to introduce a coma that compensates for the coma given by the grating. The possibility of using two interchangeable gratings made the set-up optimized for a broad energy range of 12–50 eV. As a design test case, the set-up has been applied to a selection of the discrete spectral lines emitted by a gas-discharge lamp as the XUV source, obtaining a resolving power E/ Δ E > 3000.

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