scholarly journals Metallicity effects in Mira variables: a model study

2004 ◽  
Vol 193 ◽  
pp. 313-316
Author(s):  
M. Scholz ◽  
P.R. Wood
Keyword(s):  
Surface Brightness ◽  
Moderate Deviation ◽  
Spectral Features ◽  
Mira Variables ◽  
Model Study ◽  
Solar Metallicity ◽  
Selected Effects

AbstractM-type Mira models with a moderate deviation from solar metallicity (2x and 0.5 x) have been computed and compared to solar-metallicity models. Selected effects of abundance changes on pulsation properties, atmospheric stratifications, spectral features (colours) and surface brightness distributions are discussed.

The Spectra of Red Variables: SC Stars

1979 ◽  
Vol 46 ◽  
pp. 215-222
Author(s):  
Philip C. Keenan
Keyword(s):  
Inverse Problem ◽  
Variable Star ◽  
Point Of View ◽  
The Other ◽  
Spectral Features ◽  
Spectral Classification ◽  
Mira Variables ◽  
Other Hand ◽  
Physical Variables ◽  
The One

The value of recording the spectra of red stars depends upon one’s point of view. On the one side, to those concerned with spectral classification in general, it is of the greatest aid in calibrating the criteria of classification if those criteria are observed in a variable star in which the physical variables change by a known amount. Thus the temperature differences, amounting to three or four hundred degrees, between the maximum and minimum phases of Mira variables, have helped to establish the temperature criteria that are in general use for the coolest stars.On the other hand, I am sure that at this meeting there is more interest in the inverse problem: how to use the behavior of the spectral features to learn more about what is going on in the variable star - or, at least, at their surfaces.

scholarly journals ISOSWS Spectral Variations of Oxygen-Rich Miras

1999 ◽  
Vol 191 ◽  
pp. 245-250
Author(s):  
M. J. Creech-Eakman ◽  
R. E. Stencel
Keyword(s):  
Short Wavelength ◽  
Monitoring Program ◽  
Spectral Features ◽  
Mid Infrared ◽  
Mira Variables

In conjunction with an extensive ground-based monitoring program of 32 oxygen-rich Mira variables, a subset of this sample has been monitored with phase using ISO's Short Wavelength Spectrometer (ISOSWS) and ground-based mid-infrared spectrometers. Some of the six sources will be presented here in 2.5–45 μm ISOSWS spectra and 7.5–13.5 μm ground-based spectra using CGS3. Discussion of the spectral features of SiO, CO, H2O, and silicates will be presented. These data are considered in the context of recent demonstrations of variations in the spectral features with phase of the Miras.

scholarly journals Identifying circumstellar dust around oxygen-rich mira variables with maser emission via continuum elimination

2021 ◽  
Author(s):  
◽  
Lisa Shepard
Keyword(s):  
Major Effect ◽  
Peak Position ◽  
Asymptotic Giant Branch ◽  
Correct Identification ◽  
Spectral Features ◽  
Agb Stars ◽  
Dust Grains ◽  
Maser Emission ◽  
Dust Shells ◽  
Mira Variables

Stars between about 0.8 and 8 times the mass of the Sun will eventually evolve, becoming asymptotic giant branch (AGB) stars, where they pulsate and eject mass from their atmospheres, forming dust shells in the space around them. Evolved low- and intermediate-mass stars with carbon-to-oxygen ratios (C/O) below unity are known as oxygen-rich stars. O-rich stars are surrounded by dust shells containing mineral species dominated by silicate dust grains. In this dissertation, I examine whether dust grains around evolved, oxygen-rich AGB stars have any correlation with maser emission, and to understand the connection, if any, between specific types of maser emission and dust spectral features. I have investigated several methods of continuum elimination using spectroscopy data for the archetypal dusty AGB star, Mira. I have investigated the ~10[mu]m and ~18[mu]m spectral features in the continuum-eliminated spectrum including peak position, barycenter, and full width half maxima (FWHM). The positions and widthved spectral features were compared with those seen in laboratory spectra. I then looked for a correlation between maser emission and dust spectral features in a sample of Mira variables. The types of masers have been identified, and peak positions, barycenter positions, and FWHM have been measured for the sample spectra. The results show that the method of continuum elimination matters for correct identification of dust minerals, while varying the temperature and precise continuum shapes do not have a major effect on the positions of spectral features. Observed astronomical silicate features are complex and indicate the need for different compositions of minerals. Finally, there does not appear to be a correlation between the presence of a maser and dust spectral features based on the information available for analysis.

scholarly journals Consistently Simulating a Wide Range of Atmospheric Scenarios for K2-18b with a Flexible Radiative Transfer Module

2020 ◽  
Author(s):  
Markus Scheucher ◽  
Fabian Wunderlich ◽  
John Lee Grenfell ◽  
Heike Rauer
Keyword(s):  
Radiative Transfer ◽  
Cross Sections ◽  
Rayleigh Scattering ◽  
Spectral Characteristics ◽  
Water Reservoir ◽  
Distribution Model ◽  
Spectral Features ◽  
Diverse Range ◽  
Wide Range ◽  
Solar Metallicity

<p>The atmospheres of small, potentially rocky exoplanets are expected to cover a diverse range in composition and mass. Studying such objects therefore requires flexible and wide-ranging modeling capabilities. We present here our newly developed, flexible radiative transfer module, REDFOX, validated for the Solar system planets Earth, Venus and Mars, as well as steam atmospheres. REDFOX is a k-distribution model using the correlated-k approach with random overlap method for the calculation of opacities used in the δ-two-stream approximation for radiative transfer. Opacity contributions from Rayleigh scattering, UV / visible cross sections and continua can be added selectively.</p><p>With the improved capabilities of our new model, we calculate various atmospheric scenarios for K2-18b, a super-Earth / sub-Neptune with ∼8 M⊕ orbiting in the temperate zone around an M-star, with recently observed H<sub>2</sub>O spectral features in the infrared. We model Earth-like, Venus-like, as well as H<sub>2</sub>-He primary atmospheres of different Solar metallicity and show resulting climates and spectral characteristics, compared to observed data. Our results suggest that K2-18b has an H<sub>2</sub>-He atmosphere with limited amounts of H<sub>2</sub>O and CH<sub>4</sub>. Results do not support the possibility of K2-18b having a water reservoir directly exposed to the atmosphere, which would reduce atmospheric scale heights, hence too the amplitudes of spectral features inconsistent with the observations. We also performed tests for H<sub>2</sub>-He atmospheres up to 50 times Solar metallicity, all compatible with the observations.</p>

Variation of the amount of hydrogen along the galactic ridge

1967 ◽  
Vol 31 ◽  
pp. 171-172
Author(s):  
Th. Schmidt-Kaler
Keyword(s):  
Surface Brightness ◽  
Milky Way ◽  
Neutral Hydrogen ◽  
Line Of Sight ◽  
Optical Surface ◽  
Hydrogen Density ◽  
Continuous Radiation ◽  
Galactic Longitude

The integralNHof neutral-hydrogen density along the line of sight is determined from the Kootwijk and Sydney surveys. The run ofNHwith galactic longitude agrees well with that of thermal continuous radiation and that of the optical surface brightness of the Milky Way.

Surface Brightness Scale of Galactic Cepheids

1999 ◽  
Vol 190 ◽  
pp. 561-562
Author(s):  
G. P. Di Benedetto
Keyword(s):  
Surface Brightness ◽  
Variable Stars ◽  
Giant Stars ◽  
Near Ir

An accurate calibration of the surface brightness scaleSVas a function of the near-IR color (V–K) has been recently measured for non-variable Galactic dwarf and giant stars. It can be shown that this correlation can be applied to theSVscale of Galactic Cepheid variable stars, which are of major cosmological interest.

Polarimetric Observations of Red Variables: A Study of Gas and Particle Interactions

1979 ◽  
Vol 46 ◽  
pp. 386-408 ◽  
Author(s):  
G. V. Coyne ◽  
I. S. McLean
Keyword(s):  
Wavelength Dependence ◽  
Stellar Atmosphere ◽  
Molecular Absorption ◽  
Absorption Bands ◽  
Absorption And Emission ◽  
Mira Variables ◽  
Stellar Photosphere ◽  
Regular Variable ◽  
Red Supergiants ◽  
Balmer Lines

AbstractIn recent years the wavelength, dependence of the polarization in a number of Mira variables, semi-regular variables and red supergiants has been measured with resolutions between 0.3 and 300 A over the range 3300 to 11000 A. Variations are seen across molecular absorption bands, especially TiO bands, and across atomic absorption and emission lines, especially the Balmer lines. In most cases one can ignore or it is possible to eliminate the effects due to interstellar polarization, so that one can study the polarization mechanisms operating in the stellar atmosphere and environment. The stars Omicron Ceti. (Mira), V CVn (semi-regular variable) and Mu Cephei (M2 la), in addition to other stars similar to them, will be discussed in some detail.Models to explain the observed polarization consider that the continuum flux is polarized either by electron, molecular and/or grain scattering or by temperature variations and/or geometrical asymmetries over the stellar photosphere. This polarized radiation is affected by atomic and molecular absorption and emission processes at various geometric depths in the stellar atmosphere and envelope. High resolution spectropolarimetry promises, therefore, to be a power-rul tool for studying stratification effects in these stars.

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