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.

scholarly journals Surveys for Carbon Stars in External Galaxies

2000 ◽  
Vol 177 ◽  
pp. 51-58
Author(s):  
Marc Azzopardi
Keyword(s):  
Local Group ◽  
Galactic Halo ◽  
Magellanic Clouds ◽  
Carbon Stars ◽  
Molecular Absorption ◽  
Absorption Bands ◽  
Distant Galaxies ◽  
External Galaxies ◽  
Dwarf Spheroidals

Prominent molecular absorption bands in the spectra of carbon stars make their detection possible, even in relatively distant external galaxies. Although extensive surveys for carbon stars have been carried out mainly in the Magellanic Clouds and the dwarf spheroidals in the Galactic halo, more distant galaxies in the Local Group and beyond have been successfully searched for this kind of object.

scholarly journals Luminous red novae: Stellar mergers or giant eruptions?

2019 ◽  
Vol 630 ◽  
pp. A75 ◽  
Author(s):  
A. Pastorello ◽  
E. Mason ◽  
S. Taubenberger ◽  
M. Fraser ◽  
G. Cortini ◽  
...  
Keyword(s):  
Close Binary System ◽  
Light Curves ◽  
Close Binary ◽  
Late Time ◽  
Absorption Bands ◽  
Common Envelope ◽  
Balmer Lines ◽  
Alternative Scenarios ◽  
Stellar Mergers ◽  
Second Peak

We present extensive datasets for a class of intermediate-luminosity optical transients known as luminous red novae. They show double-peaked light curves, with an initial rapid luminosity rise to a blue peak (at −13 to −15 mag), which is followed by a longer-duration red peak that sometimes is attenuated, resembling a plateau. The progenitors of three of them (NGC 4490−2011OT1, M 101−2015OT1, and SNhunt248), likely relatively massive blue to yellow stars, were also observed in a pre-eruptive stage when their luminosity was slowly increasing. Early spectra obtained during the first peak show a blue continuum with superposed prominent narrow Balmer lines, with P Cygni profiles. Lines of Fe II are also clearly observed, mostly in emission. During the second peak, the spectral continuum becomes much redder, Hα is barely detected, and a forest of narrow metal lines is observed in absorption. Very late-time spectra (∼6 months after blue peak) show an extremely red spectral continuum, peaking in the infrared (IR) domain. Hα is detected in pure emission at such late phases, along with broad absorption bands due to molecular overtones (such as TiO, VO). We discuss a few alternative scenarios for luminous red novae. Although major instabilities of single massive stars cannot be definitely ruled out, we favour a common envelope ejection in a close binary system, with possibly a final coalescence of the two stars. The similarity between luminous red novae and the outburst observed a few months before the explosion of the Type IIn SN 2011ht is also discussed.

scholarly journals Lipofuscin-Type Pigment as a Marker of Colorectal Cancer

Electronics ◽  
2020 ◽  
Vol 9 (11) ◽  
pp. 1805
Author(s):  
Sónia Carvalho ◽  
Isa Carneiro ◽  
Rui Henrique ◽  
Valery Tuchin ◽  
Luís Oliveira
Keyword(s):  
Colorectal Cancer ◽  
Optical Properties ◽  
Wavelength Dependence ◽  
Biological Tissues ◽  
Diagnostic Methods ◽  
Optical Methods ◽  
Published Data ◽  
Spectral Measurements ◽  
Absorption Bands ◽  
Colorectal Mucosa

The study of the optical properties of biological tissues for a wide spectral range is necessary for the development and planning of noninvasive optical methods to be used in clinical practice. In this study, we propose a new method to calculate almost all optical properties of tissues as a function of wavelength directly from spectral measurements. Using this method, and with the exception of the reduced scattering coefficient, which was obtained by traditional simulation methods, all the other optical properties were calculated in a simple and fast manner for human and pathological colorectal tissues. The obtained results are in good agreement with previous published data, both in magnitude and in wavelength dependence. Since this method is based on spectral measurements and not on discrete-wavelength experimental data, the calculated optical properties contain spectral signatures that correspond to major tissue chromophores such as DNA and hemoglobin. Analysis of the absorption bands of hemoglobin in the wavelength dependence of the absorption spectra of normal and pathological colorectal mucosa allowed to identify differentiated accumulation of a pigment in these tissues. The increased content of this pigment in the pathological mucosa may be used for the future development of noninvasive diagnostic methods for colorectal cancer detection.

scholarly journals Continuum Distributions and Line Profiles of UX UMa-Type Novalike Systems

1987 ◽  
Vol 93 ◽  
pp. 91-102
Author(s):  
K. Haug
Keyword(s):  
Boundary Layer ◽  
Accretion Disks ◽  
Wavelength Dependence ◽  
Stellar Atmosphere ◽  
Photometric Data ◽  
Balmer Line ◽  
Spectral Indices ◽  
Line Profiles ◽  
Orbital Inclination ◽  
Multi Wavelength

AbstractCombined UV, optical and, in part, IR continuum distributions of the UX UMa-systems CPD-48°1577, V3885 Sgr, RW Sex and of the recently discovered cataclysmic system PHL 227 were determined from multi-wavelength spectroscopic and photometric data to search for general characteristics of these systems. The observed variations of the UV to IR spectral indices are qualitatively very similar for all systems, whereas the absolute values show significant differences in the far and near UV ranges. The wavelength dependence of the optical and IR spectral indices as well as the variations of the Balmer line profiles lie within the range of model spectra of optically thick and stationary accretion disks with stellar atmosphere characteristics. The different behavior of the far UV spectral indices can be explained by the excess radiation from an extended and optically thick boundary layer, which depends mainly on the orbital inclination.

Spectrophotometry of carbon stars. III. Molecular absorption bands: Quantitative analysis

Astrophysics ◽  
1986 ◽  
Vol 24 (2) ◽  
pp. 142-149
Author(s):  
S. E. Nersisyan ◽  
R. Kh. Oganesyan
Keyword(s):  
Quantitative Analysis ◽  
Carbon Stars ◽  
Molecular Absorption ◽  
Absorption Bands

Variability of water masers in evolved stars on timescales of decades

2017 ◽  
Vol 13 (S336) ◽  
pp. 393-394 ◽  
Author(s):  
Jan Brand ◽  
Dieter Engels ◽  
Anders Winnberg
Keyword(s):  
Structural Changes ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
Mira Variables ◽  
Velocity Gradients ◽  
Systemic Velocity ◽  
Secular Variations ◽  
Red Supergiants ◽  
Water Masers

AbstractFor several decades (1987-2015) we have been carrying out observations of water masers in the circumstellar envelopes (CSE’s) of Mira variables, Red Supergiants (RSG’s) and Semi-Regular Variables (SRV’s) with the Medicina 32-m and Effelsberg 100-m antennas. The single-dish monitoring observations provide evidence for strong H2O maser profile variations, which likely are connected to structural changes in the maser shells. Such variations include strong flares in intensity lasting several (tens of) months and systemic velocity gradients of maser components developing over years, as well as other secular variations which are superimposed on periodic variations following the stellar light variations.When complemented with interferometric observations, it is possible to derive the 3-D distribution of the maser spots, and their lifetime, as we have done for RX Boo (Winnberget al.2008) and U Her (Winnberget al.2011; Brandet al. in prep.).

scholarly journals The Evolution of Hα Profiles in S-type Mira Stars

1993 ◽  
Vol 139 ◽  
pp. 209-209
Author(s):  
A.W. Woodsworth
Keyword(s):  
Shock Waves ◽  
Data Base ◽  
Strong Absorption ◽  
Emission Lines ◽  
High Dispersion ◽  
Absorption Bands ◽  
Good Data ◽  
Mira Variables ◽  
Static Models ◽  
Simple Models

Past attempts to model the Hα emission profiles from Mira stars have been hampered by the strong absorption bands produced by TiO (M-type Miras) or carbon-based molecules (C-type Miras). The S-type Miras, however, exhibit relatively clean emission lines. As part of a larger study of Mira variables, I have obtained a series of high-dispersion Hα profiles of S-type Miras at different phases, using the DAO 48” coudé spectrograph. Although most profiles were obtained from different stars, their shapes develop in a regular way with advancing phase, so it appears that the observations can be used together to provide a good data base for the fitting of evolutionary (rather than static) models for the shock waves in S-type Miras.Initial experiments with fitting simple models to the profiles have been extremely encouraging. The profiles can be represented very well by three Gaussian components.

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