Top PDF Studies of Gas Absorption In Infrared Spectra of Carbon-Rich AGB Stars

Studies of Gas Absorption In Infrared Spectra of Carbon-Rich AGB Stars

Studies of Gas Absorption In Infrared Spectra of Carbon-Rich AGB Stars

also with half reset interval, resulting in same resolving power as speed 2. Note that for all the speed modes, the recorded spectra will still have the same sampling rates across the wavelength, because the total number of samples stays the same. As a result, the integrations of these extra samples smooth the spectrum, preventing aliasing problems due to insufficient sampling. But their effective resolutions are still degraded. This means the spectrum obtained by speed mode 1 is 8 times interpolated to appear a higher spectral resolution, but its effective resolution is unchanged (Leech et al. 2003). The grating moves during a reset interval. The time line of an AOT S01 observation starts with pointing aperture 1 to target. And then it switches to aperture 2 and 3 in sequence after a single up-down scan in between to measure certain band segments. Upon completing all the up down scans, all 12 band segments will be measured. Dark current is recorded at each aperture change and at both the start and the end of each measurement. The procedure finishes with an internal photometric calibration.
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Dust features in the 10-mu m infrared spectra of oxygen-rich evolved stars

Dust features in the 10-mu m infrared spectra of oxygen-rich evolved stars

spheres of AGB stars get progressively more carbon-rich. Therefore oxygen-rich AGB stars can have carbon-to- oxygen ratios (C/O) ranging from cosmic, ∼ 0.4, to ap- proximately unity. Supergiants, on the other hand, are not expected to experience a “third dredge-up” and are there- fore expected to remain oxygen-rich, with approximately cosmic C/O. Furthermore, Sylvester et al. (1994) found UIR bands in the spectra of some M-supergiants. They suggested that UV photodissociation of CO molecules pro- vided the free carbon atoms required to form the organic materials responsible for the UIR bands. Obviously, this dissociation mechanism would also release extra oxygen atoms, and if the carbon atoms become trapped in or- ganic molecules, this could lead to an even more oxygen- rich environment (C/O < 0.4). Therefore, supergiants exhibiting the UIR bands could have even more oxy- gen available for dust formation and, following the SP98 scheme, we might expect these stars to exhibit the “clas- sic” strong silicate spectral feature, since they should have more than enough oxygen to make substantial amounts of Mg-silicates. However, many of the supergiants with UIR bands exhibit “broad” spectral features. These supergiant “broad” spectral features are alone enough to call into question a condensation mechanism based on the amount of available oxygen, since the C/O ratio for supergiants is always low. Combining this with the UIR band evidence, it seems unlikely that the type of dust forming around these stars is determined solely by the amount of oxygen available.
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Circumstellar C2, CN and CH+ in the optical spectra of post-AGB stars

Circumstellar C2, CN and CH+ in the optical spectra of post-AGB stars

spectrum of HD 56126 (Paper I) we started an extensive ob- serving campaign in order to find additional post-AGB stars with molecular absorption or emission lines. Assuming that the presence of carbon-based molecules is related to the high carbon abundance of the AGB ejecta, we have selected those stars with a carbon-rich circumstellar environment. The pres- ence of the 3.3 and 3.4-3.5 µm Polycyclic Aromatic Hydro- carbon (PAH) features and of the unidentified 21 µm feature (Kwok et al. 1989) were used as criteria for the carbon-rich nature of the AGB ejecta (Table 1). Recently the number of objects exhibiting the 21 µm feature has been extended (e.g., Henning et al. 1996, Justtanont et al. 1996), and these objects have been selected for a follow-up study. The sample was sup- plemented with those stars of special importance for the theory of post-AGB evolution (e.g., the metal-depleted post-AGB bina- ries: HD 52961, HR 4049, BD +39 o 4926, Red Rectangle, and HD 213985). Two O-rich post-AGB stars (e.g, HD 161796 and IRAS 08005-2356) were added to see whether O-rich star have the carbon based molecules, and the well studied carbon star IRC+10216 was added to the list, since its spectrum could pos- sibly be used as a template for identifying molecular features. With a limiting magnitude of m v = 14 this resulted in a list of sixteen Post-AGB stars (and IRC +10216) observable from La Palma. IRAS 05341+0852 was added to the list at a later stage. The optical spectrum and the molecular bands are described by Reddy et al. (1997).
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Study and Analysis of Absorption
Spectra of Quasars

Study and Analysis of Absorption Spectra of Quasars

A quasi-stellar radio source (quasar) is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high red shift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than extended sources similar to galaxies. The simplest way to explain the quasar's red shifts is to assume that they are extremely distant bodies that follow Hubble's law. In this paper, eight single and four double quasars have been detected from SDSS .The single quasars are: SDSS J100120.82+555349.8, SDSS J095918.70+020951.5 ,SDSS J093857.01+412821.2 , SDSS J141647.21+521115.5, SDSS J141030.62+511113.8 , SDSS J005006.35-005319.2 ,SDSS J000552.33- 000655.6 and SDSS J222851.23+011432.3 ,the double quasars are SDSS J115518.29+193942.2, SDSS J162026.14+120342.0, SDSS J133907.13+131039.6 and J125418.94+223536.5. For both types quasars , chemical composition are determined and the redshift are measured from the absorption spectra, it found that the single quasars spans a redshift range of 0.335 ≤ z ≤ 6.47. the; and double quasars spans a redshift of 1.01 ≤ z ≤ 3.64. Applying Hubble's law to these values of redshift, some features of absorption line of quasars are measured and analyzed.
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Electronic absorption spectra of mantle minerals

Electronic absorption spectra of mantle minerals

A spectrum obtained from a 300pm thick plate o f ferropericlase containing 2.5%Fe^^ and no Fe^\ is shown in Fig. 7.1. The spectrum contains one main absorption feature around lOOOOcm’^ and is in good agreement with that obtained by Goto et al (1980) for (Mg?4, Fe26 )0 . Using this spectrum vdiich shows an absorption band extending from 6000 to 17000cm B um s ( 1993) assigned maxima to 10000 and 11600cm'\ Similarly Fig. 7.1 shows maxima at approximately 9300 and 11200cm'\ This large feature is due to the ^Tzg spin allowed transition o f Fe^^ modified by dynamic Jahn - Teller splitting. In order to obtain more accurate peak positions Gaussian curves were fit to the spectrum It was not possible, however, to reproduce the spectrum with only two curves, and the best fit was obtained from a minimum o f four Gaussian conponents at 7644, 9307, 11175 and 13458cm *, some o f which are exceptionally wide (Table 7.1). The presence o f so many bands and their widths can be explained by the thermal vibrations o f the atoms in the structure. As the ions in the sanple osdllate about their mean positions, the value o f \ will also oscillate about a mean value reflecting the mean position o f the atoms. As the energy separation between t2g and eg orbitals for Fe^^ is sensitive to variation in the position o f an absorption band will vary with A (Bums, 1993). When combined with the dynamic Jahn - Teller plitting, it is likely that this is an eplanation for the features seen in the curve fitting process. The less intense peaks above 17000cm:* are possibly p in forbidden transitions o f Fe^\
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A theoretical study on absorption spectra of ofloxacin

A theoretical study on absorption spectra of ofloxacin

Ofloxacin molecule was modeled using Avogadro [26]. The ground state geometry was optimized using DFT/B3LYP hybrid functional with 6-31G(d,p) basis sets. The effect of solvent (ethanol) was added using the polarizable continuum model (PCM) of solvation. The optimized geometries are utilized to get the frontier molecular orbitals and to carry out the TDDFT studies. λ max of ofloxacin is calculated at the level of TDDFT/6-

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The ALMA detection of CO rotational line emission in AGB stars in the Large Magellanic Cloud

The ALMA detection of CO rotational line emission in AGB stars in the Large Magellanic Cloud

If Eq. 2 is applicable and the dust-based MLRs are correct then the CO abundances must be substantially lower (by an or- der of magntiude) than assumed, and/or the observed CO inten- sities are lower by a factor of ∼ 7 for the C-stars and > 30 for the OH/IR stars than expected based on Eq. 2. The dust emission and the CO J= 2-1 emission trace different radii in the envelope, so one possible explanation for this difference between dust and CO based mass-loss rate is that it varies in time, a suggestion first made by Heske et al. (1990) in connection with Galactic OH/IR stars. Another possibility is that the interstellar radiation field (ISRF) is stronger in the LMC. Paradis et al. (2009) men- tion that, assuming the same spectral shape for the ISRF as in the solar neighborhood, the ISRF in the diffuse LMC medium is ∼ 5 times stronger. The strength of the [C ii ] line relative to CO in LMC star-forming regions is much larger than in Milky Way ones, also pointing to a stronger radiation field (Israel & Maloney 2009). Recent work by McDonald et al. (2015) and Zhukovska et al. (2015) have demonstrated the importance of the strength of the ISRF on the expected CO emission in clusters. That the largest difference between CO-based and dust-based MLR is observed for the IRAS 05298, which is known to be in a cluster, is consistent with this. The influence of the ISRF and a full line radiative transfer modeling is deferred until the CO J= 3-2 lines have been measured by ALMA.
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Predicting ambient aerosol thermal-optical reflectance (TOR) measurements from infrared spectra: organic carbon

Predicting ambient aerosol thermal-optical reflectance (TOR) measurements from infrared spectra: organic carbon

Abstract. Organic carbon (OC) can constitute 50 % or more of the mass of atmospheric particulate matter. Typically, or- ganic carbon is measured from a quartz fiber filter that has been exposed to a volume of ambient air and analyzed using thermal methods such as thermal-optical reflectance (TOR). Here, methods are presented that show the feasibility of us- ing Fourier transform infrared (FT-IR) absorbance spectra from polytetrafluoroethylene (PTFE or Teflon) filters to ac- curately predict TOR OC. This work marks an initial step in proposing a method that can reduce the operating costs of large air quality monitoring networks with an inexpen- sive, non-destructive analysis technique using routinely col- lected PTFE filter samples which, in addition to OC concen- trations, can concurrently provide information regarding the composition of organic aerosol. This feasibility study sug- gests that the minimum detection limit and errors (or un- certainty) of FT-IR predictions are on par with TOR OC such that evaluation of long-term trends and epidemiological studies would not be significantly impacted. To develop and test the method, FT-IR absorbance spectra are obtained from 794 samples from seven Interagency Monitoring of PRO- tected Visual Environment (IMPROVE) sites collected dur- ing 2011. Partial least-squares regression is used to calibrate sample FT-IR absorbance spectra to TOR OC. The FTIR spectra are divided into calibration and test sets by sampling site and date. The calibration produces precise and accu- rate TOR OC predictions of the test set samples by FT-IR as indicated by high coefficient of variation (R 2 ; 0.96), low bias (0.02 µg m −3 , the nominal IMPROVE sample volume is 32.8 m 3 ), low error (0.08 µg m −3 ) and low normalized er- ror (11 %). These performance metrics can be achieved with various degrees of spectral pretreatment (e.g., including or
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Polarized absorption spectra of purines and pyrimidines

Polarized absorption spectra of purines and pyrimidines

By determining transition dipole moment directions for the various absorption band s and by knowing the cry stal s tr u cture one can test the Tinoco or Rhodes theory for intensity behav[r]

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Infrared spectra of ternary CTCS of TMPD

Infrared spectra of ternary CTCS of TMPD

centers in the TCNQ complex. The acoustic phonon scattering reveals more conduction in TCNE complex. Finally, the electronic absorption envelope at very low frequency (below 800 cm -1 ) has a Gaussian shape in the TCNE complex while the same has square-power beta density shape in the TCNQ complex. The envelope is broader in the TCNE complex than that in the TCNQ complex indicating stronger electron-phonon interaction in the TCNE complex than in the TCNQ complex. The four spectra of these four ternary complexes shows noise in the free-carrier absorption region above 3600 cm -1 as expected in photoconductors and noise in the region of localization near the band edges. The TCNQ and TCNE complexes shows an asymmetric triangular distribution marked as T.D. in the mid-IR range due to either an internal Franz- Keldysh effect or due to imperfect nesting of the Fermi surface.
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The Effect of Infrared Light’s Power on the Infrared Spectra of Thin Films

The Effect of Infrared Light’s Power on the Infrared Spectra of Thin Films

atomic layer deposition. We find that different values of P of the IR light dis- place the minima of the absorption bands. This effect is reproducible in dif- ferent sets of experiments and in different spectrometers. To interpret the experimental findings, we use the law of conservation of energy. We find a correlation among the energy of the IR waves and the number, moment of inertia, and vibrational/rotational frequency of the bonds involved in the vi- brational or rotational motion. The law of conservation of energy unveils that larger values of P of the IR light and lower wavenumbers of the resonances involve a larger number of crystal bonds. One practical application of our approach is that it suggests a way to improve the sensitivity of the FTIR spec- tra of thin crystalline films in the far IR region.
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Predicting ambient aerosol thermal–optical reflectance measurements from infrared spectra: elemental carbon

Predicting ambient aerosol thermal–optical reflectance measurements from infrared spectra: elemental carbon

Abstract. Elemental carbon (EC) is an important constituent of atmospheric particulate matter because it absorbs solar ra- diation influencing climate and visibility and it adversely af- fects human health. The EC measured by thermal methods such as thermal–optical reflectance (TOR) is operationally defined as the carbon that volatilizes from quartz filter sam- ples at elevated temperatures in the presence of oxygen. Here, methods are presented to accurately predict TOR EC using Fourier transform infrared (FT-IR) absorbance spec- tra from atmospheric particulate matter collected on poly- tetrafluoroethylene (PTFE or Teflon) filters. This method is similar to the procedure developed for OC in prior work (Dillner and Takahama, 2015). Transmittance FT-IR analy- sis is rapid, inexpensive and nondestructive to the PTFE filter samples which are routinely collected for mass and elemental analysis in monitoring networks. FT-IR absorbance spectra are obtained from 794 filter samples from seven Interagency Monitoring of PROtected Visual Environment (IMPROVE) sites collected during 2011. Partial least squares regression is used to calibrate sample FT-IR absorbance spectra to col- located TOR EC measurements. The FT-IR spectra are di- vided into calibration and test sets. Two calibrations are de- veloped: one developed from uniform distribution of sam- ples across the EC mass range (Uniform EC) and one devel- oped from a uniform distribution of Low EC mass samples (EC < 2.4 µg, Low Uniform EC). A hybrid approach which applies the Low EC calibration to Low EC samples and the Uniform EC calibration to all other samples is used to pro- duce predictions for Low EC samples that have mean error on par with parallel TOR EC samples in the same mass range and an estimate of the minimum detection limit (MDL) that is on par with TOR EC MDL. For all samples, this hybrid
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AKARI All Sky Survey: contribution from AGB stars to the far infrared flux from the Milky Way related to point sources outside the Galactic plane

AKARI All Sky Survey: contribution from AGB stars to the far infrared flux from the Milky Way related to point sources outside the Galactic plane

ponent of dust emission, all-sky far-IR survey data are desirable. The Infrared Astronomical Satellite (IRAS; Neugebauer et al., 1984) has brought a vast amount of statistics and very efficient methods of analysis have been devised from the IRAS Point Source Catalog (PSC). The four bands of IRAS have enabled us even to perform a very detailed classification of extragalactic and various galactic objects, like blue and red galaxies, Seyferts and QSOs, car- bon stars, H II regions, reflection nebulae, planetary nebulae, T Tauri stars, etc. Hacking et al. (1985) classified the stars on the IRAS color-color plane, and found that C- and O- rich stars occupy a separated region different from that for normal stars. Thronson et al. (1987) showed a distinction between C- and O-rich stars based on IRAS colors. Van der Veen and Habing (1988) introduced ten zones for the de- tailed classification of IRAS-detected stars, which was later extensively used by Busso et al. (1996). Walker and Cohen (1988) also defined occupation zones for stars. A thorough description of the IRAS color-color classification method including extragalactic objects and star-forming regions can be found in, e.g., Walker et al. (1989).
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Column abundances of carbon dioxide and methane retrieved from ground-based near-infrared solar spectra

Column abundances of carbon dioxide and methane retrieved from ground-based near-infrared solar spectra

The column measurements described in this work were acquired at an automated observatory located at the WLEF Tall Tower site in Northern Wisconsin. The observatory was developed for highly precise, ground-based solar absorption spectrometry, and it is the first dedicated observatory in the Total Carbon Column Observing Network (TCCON). Solar tracking optics and a Fourier Transform Spectrometer (FTS) are used to record near- infrared spectra of the sun at high spectral resolution. Solar spectra are acquired continuously during clear sky conditions, with each spectrum requiring ~110 seconds. Details regarding the FTS observatory and analysis technique can be found in Washenfelder et al. [2006]. Measurement precision of ~0.1% is demonstrated for retrievals of column CO 2 and column O 2 under clear-sky conditions [Washenfelder et al., 2006].
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Terahertz absorption spectra of short chain peptides

Terahertz absorption spectra of short chain peptides

The Infrared (IR) spectra of the pure crystallized samples were taken from 400cm -1 -4000cm -1 at room temperature with instrument resolution set at 2cm -1 by Fourier Transform Infrared-Attenuated Total Internal Reflector (FTIR-ATR) Spectrometer (α-FTIR-ATR: Bruker Optics Inc). The instrument is equipped with standard mid-IR beam splitter (T303) measured with standard mid-IR source (low voltage / air cooled) and DTGS (KBr/Dla TGSD301) detector which S/N> 4×10 8

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Laboratory Gas-phase Infrared Spectra of Two Astronomically Relevant PAH Cations: Diindenoperylene, C32H16+ and Dicoronylene, C48H20+

Laboratory Gas-phase Infrared Spectra of Two Astronomically Relevant PAH Cations: Diindenoperylene, C32H16+ and Dicoronylene, C48H20+

The experiments described here have been performed with iPoP, our fully mobile “ instrument for Photo-dissociation of PAHs ” ( Zhen et al. 2014b ) . The set-up has been used at one of the end stations of FELIX, the Free Electron Laser for InfraRed eXperiments at Radboud University ( Oepts et al. 1995 ) . The information on the experimental procedures is available from ( Zhen et al. 2017 ) . Here, only the relevant details are provided. The two central parts of iPoP are a quadrupole ion trap ( QIT ) and a time-of- fl ight ( TOF ) mass spectrometer. Gas-phase DIP and DC precursor molecules are obtained by heating commercially available powder ( Kentax, purity higher than 99.5% ) in an oven that can be preset to a value very close to the sublimation temperature: ∼ 480 K for DIP and ∼ 670 K for DC. The gas-phase neutrals are ionized using electron impact ionization, typically with 83  eV electron impact energy. The resulting DIP + and DC + cations enter in the QIT via an ion gate and are trapped by applying a 1 MHz radiofrequency electric fi eld ( 3000 and 3280 V p–p ) onto the ring electrode. Helium that is continuously introduced into the ion trap thermalizes the ion cloud.
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A method for normalization of X ray absorption spectra

A method for normalization of X ray absorption spectra

We have shown that the MBACK algorithm is reliable and reproducible, and, providing a sufficient range of data is available, is mathematically stable. To the extent that the McMaster tables that are used for reference are accurate, MBACK can also provide accurate absorption coefficients. However, for most applications, accuracy is less important than precision. We have shown that MBACK provides suffi- cient precision to distinguish chemically induced spectral changes that are obscured by conventional normalization procedures. Beyond detailed comparison of XANES spectra, MBACK should be useful for other analyses that depend on careful edge normalization. One such example is the moment method for determining edge energies (Alp et al., 1989). This approach shows promise for avoiding the sensitivity of energy (defined as the first inflection point) to the shape of the edge, thus providing a more reliable determination of the oxidation state of metalloproteins (DeMarois, 1999). However, the moment method requires integration across the edge, and is thus sensitive to the details of the normalization. To avoid this sensitivity, Iuzzolino et al. (1998) have limited integrations to
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Improved retrieval of gas abundances from near-infrared solar FTIR spectra measured at the Karlsruhe TCCON station

Improved retrieval of gas abundances from near-infrared solar FTIR spectra measured at the Karlsruhe TCCON station

by the overlaying collision-induced absorption (CIA). This corroborates earlier studies by Dohe (2013) using PROFFIT (Hase et al., 2004), which also indicated reduced air-mass de- pendence when using a refined treatment of the background continuum level. The approach includes a fit of the empirical background based on a user-selectable number of baseline points which are evenly distributed across the fitted spec- tral window. A single point is equivalent to a scaling fac- tor, two points are used to create a linear fit, three or more points create a smooth background, very similar to a cubic spline fit through these guiding points. This choice has been made because each associated derivative is spectrally local- ized, whereas the fitting of parameters shaping a global poly- nomial fit across the spectral window results in derivatives which are all strongly interwoven. Dohe demonstrated that a detailed model of the O 2 CIA which overlaps the 1.26 µm
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An infrared study of mass loss from hot stars

An infrared study of mass loss from hot stars

from Humphreys (1978), where necessary these have been supplem ented by d a ta from Barlow and Cohen (1977), A bbott et al. (1980), A bbott et al. (1981) and BAC. The term inal velocities have largely been taken from P rinja et al. (1990) who have estim ated Voo from UV P Cygni profiles by the m ethod described in Section 1.3.2, the three exceptions to this are HD 169454, for which the value of v was taken from BAC, and P Cyg and HD 94910 (AG Car) for which the values of v were taken from Barlow (1991), as was the mass loss rate of AG Car. It has recently been found (P rinja et al., 1989 and subsequent Erratum) th a t some of the term inal velocities calculated by P rin ja et al. are in error and it has been necessary to apply a correction to their values of v<*, for HD 36486, HD 37043 and HD 149757 to obtain the values given in Table 5.1. The stellar radii were determined by fitting a Kurucz model atm osphere to the UV and optical energy distribution of each star. A search was made of the IU E ULDA low resolution database at RAL and the resulting spectra were combined w ith Johnson and Mitchell (1975) 13-colour photom etry and the photom etry from Table 2.9 to produce U V -IR energy distributions for the stars. The photom etry was converted from magnitudes to fluxes using the zero m agnitude calibration based on the Kurucz model for Vega w ith the empirical corrections, given in Column 5 of Table 2.3. These energy distributions were plotted using the DIPSO package (Howarth and Murray, 1987) and Kurucz model atmospheres were fitted by normalising them to the V band photom etric point using the ATNORM routine which calculates the normalising constant -R*(R@)/D(kpc); since we know the distances to the stars the radii can then be calculated. For the m ajority of the stars the normalised model atmosphere which gave the best fit to the UV and optical d ata had values of T eg and log^r which corresponded closely to the values appropriate for the spectral type of the star, i.e. those given in Table 3.3. Notable exceptions to this are P Cyg, for which the best fit was obtained with T tg = 18000 K, log <7 = 2.05 rather than the values of 19600 K and 2.4 from Table 3.3, and HD 169454 for which a fit could not be made to the IU E d a ta due to the abnorm al extinction law known to exist towards this star (Seab et al., 1981). The T eg = 18000 K, log <7 = 2.05 model also gave the best fit to the energy distribution of AG Car. This
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Asymmetry of Lines in the Spectra of the Sun and Solar-Type Stars

Asymmetry of Lines in the Spectra of the Sun and Solar-Type Stars

Stellar bisectors show significant differences both in the shape and the magnitude of the blue span with variations in effective temperature, luminosity class, or gravity. According to the results of stellar spectra studies [3, 11, 12, 13, 18, 19, 21, 22, 38], the bisector does not show the C-shape in all cold FGK stars of the main sequence; this shape is often slightly distorted, and sometimes only the upper part of the letter C is visible. The differences in shape from one star to another depend on the strength of granulation and the structure of the atmosphere. The span or shift of the bluest point of the bisector, which characterizes the average granulation velocity of the star, decreases from F- to K-stars. For giants, the span is larger than for dwarfs. The brighter the star (or the greater the luminosity, or the smaller the gravity), the lower the height of the bluest point of the bisector, and the higher the granulation penetrates into the atmosphere. The spectra of stars with a very low metal abundance reveal a significantly greater line asymmetry and a wider range of velocities than stars of the same class with solar metallicity [3]. This fact is interpreted as a signature of a low metal abundance and, therefore, a low opacity in convective atmospheres. There is also another feature of asymmetry: if we proceed along the main sequence towards higher temperatures, the line bisectors in the F0 zone change their tilt to the opposite direction. This boundary separating the two modes is called the granulation boundary [21, 23]. It is assumed that convection in hot F0V stars is qualitatively different: granules are small and quickly rise upward, while intergranules are large and descend slowly.
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