β Lyrae: a new constraint on the radiation characteristics of the accretion disc rim

A new composite model eliminates discrepancies between synthetic spectra for the L2000 model of β Lyrae and spectrophotometric scans and charge-coupled device (CCD) spectra of that binary star. The source of the discrepancies is the use of synthetic spectra from standard model atmospheres to represent the radiation characteristics of the accretion disc rim. Substitution of a composite synthetic spectrum to represent the accretion disc rim eliminates the discrepancies and produces accordance with both scan data, including their temporal variation, and CCD spectra.     

Synthetic high-resolution near-IR spectra of the Sun for planetary data reductions made from ATMOS/Spacelab-3 and Atlas-3 data

We have constructed synthetic solar spectra for the 2302-4800 cm⁻¹ (2.08-4.34 μm) range, a spectral range where planetary objects mainly emit reflected sunlight, using ATMOS (Atmospheric Trace Molecule Spectroscopy)/Spacelab-3 and Atlas-3 spectra, of which resolution is 0.01 cm⁻¹. We adopted Voigt line profiles for the modeling of line shapes based on an atlas of line identifications compiled by Geller [Geller, M., 1992. Key to Identification of Solar Features. A High-Resolution Atlas of the Infrared Spectrum of the Sun and the Earth Atmosphere from Space. NASA Reference Publ. 1224, vol. III. NASA, Washington, DC, pp. 1-22], who derived solar line positions and intensities from contaminated high-resolution solar spectra obtained by ATMOS/Spacelab-3. Because the ATMOS spectra in these wavelength ranges are compromised by absorption lines of molecules existing in Earth's high-altitude atmosphere and in the compartment of the spacecraft, the direct use of these high-resolution solar spectra has been inconvenient for the data reductions of planetary spectra. We compared the synthetic solar spectra with the ATMOS spectra, and obtained satisfactory fits for the majority of the solar lines with the exception of abnormal lines, which do not fit with Voigt line profiles. From the model fits, we were able to determine Voigt line parameters for the majority of solar lines; and we made a list of the abnormal lines. We also constructed telluric-line-free solar spectra by manually eliminating telluric lines from the ATMOS spectra and filling the gaps with adjacent continua. These synthetic solar spectra will be useful to eliminate solar continua from spectra of planetary objects to extract their own intrinsic spectral features.     

Carbon monoxide in low-mass dwarf stars

We compare high-resolution infrared observations of the CO 2–0 bands in the 2.297–2.310 μm region of M dwarfs and one L dwarf with theoretical expectations. We find a good match between the observational and synthetic spectra throughout the 2000–3500 K temperature regime investigated. None the less, for the 2500–3500 K temperature range, the temperatures that we derive from synthetic spectral fits are higher than expected from more empirical methods by several hundred kelvin. In order to reconcile our findings with the empirical temperature scale, it is necessary to invoke warming of the model atmosphere used to construct the synthetic spectra. We consider that the most likely reason for the back-warming is missing high-temperature opacity due to water vapour. We compare the water vapour opacity of the Partridge–Schwenke line list used for the model atmosphere with the output from a preliminary calculation by Barber & Tennyson. While the Partridge–Schwenke line list is a reasonable spectroscopic match for the new line list at 2000 K, by 4000 K it is missing around 25 per cent of the water vapour opacity. We thus consider that the offset between empirical and synthetic temperature scales is explained by the lack of hot water vapour used for computation of the synthetic spectra. For our coolest objects with temperatures below 2500 K, we find best fits when using synthetic spectra which include dust emission. Our spectra also allow us to constrain the rotational velocities of our sources, and these velocities are consistent with the broad trend of rotational velocities increasing from M to L.     

Circumstellar clouds derived from ultraviolet stellar spectra

It is shown that the observed variety in macrostructures of continuous spectra in the ultraviolet (2000–3000 Å) of hot stars is a result of the presence of circumstellar clouds around such stars. A method for calculations of synthetic spectra, originating as a result of passage of central star photospheric radiation through its own circumstellar cloud, is developed. It introduces a new idea of spectral class for circumstellar cloud, and a recommended method for its determination depending from the spectral class of central star and cloud's parameters (Figure 2). The results of calculations of synthetic spectra for the four combinations of system star+cloud are presented (Figures 7-10). The strongest influence of circumstellar cloud in ultraviolet is discovered on A-class stars (Figure 13). Graphic relations are introduced for determination of cloud power by observed parameters of synthetic spectra (Figures 14 and 15).It establishes an important fact for an understanding of the nature of circumstellar clouds and processes occurring in them, according to which the selective absorption in such clouds stimulatesresonance lines only, the largest number of which lies in the ultraviolet in the region of 2100–2600 Å (Figure 1). An absence of visible signs of the effect of circumstellar clouds on continuous spectra of stars in visual region can be explained by a very small number of resonance lines in this region.Lastly, the possibility of determination of physical and geometric parameters of circumstellar clouds from stellar continuous spectra in the ultraviolet is analysed.     

Mars: Far-infrared spectra and thermal-emission models

Spectra of Mars from 100 to 360 cm^?1 were obtained during three different observation periods from NASA's Kuiper Airborne Observatory. Also, a new thermal model was constructed for the surface of Mars, and synthetic spectra were computed from the models to compare with the observations. The models include the effects of a dusty atmosphere which absorbs, scatters, and reradiates energy. The synthetic spectra show significant effects on disk-averaged brigthness temperatures, as well as absorption features, due to silicate dust. The spectra of Mars, which are ratios of Mars to the Moon, do not fit the synthetic spectra unless the surface emissivities of Mars and the Moon have different dependencies on wavelenght. A possible explanation for this behavior is a difference in soil particle-size distributions between Mars and the Moon, with Mars being depleted in large particles compared to the Moon. Small particles are consistent with clay minerals which have been suggested elsewhere as constituents of the Martian surface.     

Rotational and vibrational temperatures of BaO from a barium release at 170 km, and the synthetic spectrum of BaO in the region 4700 Å to 15,500 Å

Band spectra of BaO covering a total wavelength region of 5050 Å-9300 Å were recorded from the ground with a scanning spectrophotometer at 7.1 Å resolution during a series of barium rocket releases at College, Alaska in the Spring of 1969. Rotational and vibrational temperatures, both equal to approximately 850°K at the release altitude of 170 km, were inferred by matching the release spectra with calculated synthetic spectra. This temperature persisted throughout the observing period, from release + 20 sec to 14 min after release.

Analysis of the BaO band spectrum over a large wavelength region reveals that rotational temperatures are best determined at wavelengths below 5500 Å, and that vibrational temperatures should be measured at wavelengths greater than 5500 Å. Comparisons with synthetic spectra show that several broad emission features in the release spectra, located at about 7900 Å 8400 Å and 9000 Å, may be identified as clusters of overlapping BaO bands. A synthetic spectrum of BaO extending from 4700 Å to 15,000 Å is included for general reference and to facilitate future studies in that wavelength region.     

Synthetic stellar and SSP libraries as templates for Gaia simulations

ESA’s Gaia mission will collect low resolution spectroscopy in the optical range for ～10⁹ objects. Complete and up-to-date libraries of synthetic stellar spectra are needed to built algorithms aimed to automatically derive the classification and the parametrization of this huge amount of data. In addition, libraries of stellar spectra are one of the main ingredients of stellar population synthesis models, aiming to derive the properties of unresolved stellar populations from their integrated light. We present (a) the newly computed libraries of synthetic spectra built by the Gaia community, covering the whole optical range (300–1100 nm) at medium-high resolution of (0.3 nm) for stars spanning the most different types, from M to O, from A-peculiar to Emission lines to White Dwarfs, and (b) the implementation of those libraries in our SSP code (Tantalo in The Initial Mass Function 50 Years Later, 327:235 2005), exploring different stellar evolution models.     

Lithium abundances in atmospheres of carbon stars estimated with the help of modern lists of spectral lines

We determine lithium abundances in atmospheres of three carbon stars from synthetic spectrum fitting in the λλ 668–674 nm range using the Li I λ 670.8 nm resonance doublet. To produce synthetic spectra, we use a modified list of atomic lines from the VALD database and three alternative line lists of CN and C₂ molecules which are modifications of line lists from the Jorgensen’s website () and from the Kurucz database (1993, CD-ROM nos. 1–23). The spectral lines from these lists were tested by matching synthetic spectra to observed spectra of the sun, Arcturus, and early R star HD 100764. We perform analysis of the blends involving the Li I λ 670.8 nm doublet in spectra of N stars AW Cyg and UX Dra. The lithium abundances in HD 100764, AW Cyg, and UX Dra are estimated to be lgN(Li) ≈ 2, −1.4, and −0.9, respectively. Discrepancies of lithium abundances lgN(Li) obtained with the help of molecular line lists do not seem to exceed 0.2 dex.     

The metallicity of CM Draconis

We compare observations of the eclipsing binary system CM Draconis (hereafter CM Dra) with synthetic spectra computed using the stellar atmosphere code phoenix . High-resolution infrared spectroscopic observations of six 0.05-μm-wide regions between 1.51 and 2.45 μm, combined with previous work, particularly CM Dra's accurately known surface gravity, enable us to estimate its metallicity using detailed spectral synthesis. We find significant discrepancies between the observed and synthetic spectra throughout most of the region emphasizing the need for higher quality atomic data in the infrared. Nevertheless, the     CO bands beyond 2.3 μm seem to be well modelled and metal-sensitive, and thus high-resolution spectra should be a most powerful diagnostic tool for spectroscopic analyses for M dwarfs and brown dwarfs. The CO bands indicate a metallicity of around −1 dex for CM Dra. This result is supported by observations of two M dwarfs of similar spectral type, GJ 699 (Barnard's star) and GJ 725B. This result supports inferences from previous infrared work, although it does not agree with standard evolutionary models or optical analyses, which both suggest an abundance for CM Dra close to that of the Sun.     

Analysis of disturbances in the Planetary Fourier Spectrometer through numerical modeling

Fourier transform spectrometers are instruments with high sensitivity to many kinds of disturbances. This study started from the analysis of the disturbances related to mechanical vibrations on the PFS FTIR spectrometer to show how the measured spectra can differ from the actual ones. The complete study, more in general, accounts for the characteristics of a real instrument and its operating environment to show, which can be the effects of many sources of disturbances on realistic measurements. The analysis is especially relevant when the spectra are used for the determination of parameters through “best fitting techniques” by matching with synthetic ones because it shows how spectral features used in these studies can be modified by disturbances. A previous work addressed the theoretical treatment of vibrations borne effects on FTIR spectrometers and is the ground work for the present; however, that study, being based on an analytical approach could only show examples of single effects on simplified input signals such as emission lines. This study conversely is based on a numerical model, developed in order to include altogether the effects addressed in the theoretical work to show combined effects on complex spectra like those expected from Mars. This allows not only to evaluate the linked effects of many kinds of disturbances but also to account for the real spectrometer characteristics. The use of synthetic spectra as input allows the comparison between expected spectra and measured ones. The simulation is tailored on the Planetary Fourier Spectrometer (PFS), onboard the ESA Mars Express spacecraft, from 2003 orbiting around Mars and in particular on its short wavelength (SW) channel, where many disturbances are more evident.     

Effect of atmospheric dust loading on martian albedo measurements

This work is devoted to the analysis of the variation of albedo measured by orbiting instruments with atmospheric opacity on Mars. The study has been conduced by analysing Mars Global Surveyor Thermal Emission Spectrometer (MGS-TES) data from martian regions with different surface albedo.In support of these data, synthetic spectra with different surface albedo and atmospheric opacities have been computed, so that a comparison has been performed. The synthetic spectra have been retrieved by using two different grain sizes for suspended dust (0.5 and 1.2 μm), allowing a comparison between the two models and the observations.Using the DCI, a parameter describing the quantity of dust deposited on the surface, the effectiveness of the single scattering approximation has been tested for low atmospheric opacity by analysing the quality of the linear fit up to different atmospheric opacity.For more opaque conditions two kinds of fits have been applied to the data, linear and second-order degree polynomial. In this case, we found that the polynomial fit better describes the observations.The analysis of these data made it possible to notice a peculiar trend, already reported by Christensen (1988), of the albedo over Syrtis Major after the occurrence of dust storms, but, differently from that work, now the study of DCI together with atmospheric opacity and albedo allowed us to robustly confirm the hypothesis made by Christensen.Finally, the comparison between observations and synthetic spectra computed with models with different particles grain sizes indicates that dust particles of 0.5 μm diameter are the most effective to change the aerosol atmospheric opacity on Mars.     

The Super Metal Rich Component of the Galaxyx/atl>

We present the results obtained by comparing mid-resolution stellar spectra of super metal rich candidates with synthetic spectra computed in the wavelength range 4850–5400 Å. Atmospheric parameters, derived by using the flux fitting method, are illustrated for a sample of representative stars. The final aim of the project is the definition of a fully consistent metallicity scale for SMR stars.     

CNO abundances from pre-maximum spectra of Nova Cygni 1975

Coudé spectra of Nova Cygni 1975 have been compared with LTE synthetic spectra and abundances derived for carbon, nitrogen, and oxygen. It was found that while carbon is not enhanced over the solar value, nitrogen and oxygen are substantially over-abundant by factors of at least 30 and 10, respectively. These results can be compared with analyses performed on the nebular spectrum.     

Analysis of the lithium lines in the atmosphere of the roAp star HD 24712

We use the synthetic spectrum technique to analyze two lithium lines in the spectrum of the roAp star HD 24712. The synthetic spectra are calculated in the ranges λλ 610.2–610.4 nm and 670.5–670.8 nm. We take into account the magnetic splitting of the lines and their blending by the lines of rare-earth elements. The effect of the magnetic field on absorption lines is estimated by the synthetic spectrum software SynthM developed by S.A. Khan. The upper limit for the lithium abundance turns out to be log N/N _tot = ?10.0.     

Jovian auroral spectroscopy with FUSE: analysis of self-absorption and implications for electron precipitation

High-resolution (∼0.22 Å) spectra of the north jovian aurora were obtained in the 905-1180 Å window with the Far Ultraviolet Spectroscopic Explorer (FUSE) on October 28, 2000. The FUSE instrument resolves the rotational structure of the H₂ spectra and the spectral range allows the study of self-absorption. Below 1100 Å, transitions connecting to the v^″?2 levels of the H₂ ground state are partially or totally absorbed by the overlying H₂ molecules. The FUSE spectra provide information on the overlying H₂ column and on the vibrational distribution of H₂. Transitions from high-energy H₂ Rydberg states and treatment of self-absorption are considered in our synthetic spectral generator. We show comparisons between synthetic and observed spectra in the 920-970, 1030-1080, and 1090-1180 Å spectral windows. In a first approach (single-layer model ), the synthetic spectra are generated in a thin emitting layer and the emerging photons are absorbed by a layer located above the source. It is found that the parameters of the single-layer model best fitting the three spectral windows are 850, 800, and 800 K respectively for the H₂ gas temperature and 1.3×¹⁰¹⁸, 1.5×¹⁰²⁰, and 1.3×¹⁰²⁰ cm−2 for the H₂ self-absorbing vertical column respectively. Comparison between the H₂ column and a 1-D atmospheric model indicates that the short-wavelength FUV auroral emission originates from just above the homopause. This is confirmed by the high H₂ rovibrational temperatures, close to those deduced from spectral analyses of H⁺₃ auroral emission. In a second approach, the synthetic spectral generator is coupled with a vertically distributed energy degradation model, where the only input is the energy distribution of incoming electrons (multi-layer model ). The model that best fits globally the three FUSE spectra is a sum of Maxwellian functions, with characteristic energies ranging from 1 to 100 keV, giving rise to an emission peak located at 5 μbar, that is ∼100 km below the methane homopause. This multi-layer model is also applied to a re-analysis of the Hopkins Ultraviolet Telescope (HUT) auroral spectrum and accounts for the H₂ self-absorption as well as the methane absorption. It is found that no additional discrete soft electron precipitation is necessary to fit either the FUSE or the HUT observations.     

Spectral analysis of water vapour in cool stars

M-star spectra, at wavelengths beyond 1.35 μm, are dominated by water vapour, yet terrestrial water vapour makes it notoriously difficult to obtain accurate measurement from ground-based observations. We have used the short-wavelength spectrometer on the Infrared Space Observatory at four wavelength settings to cover the  2.5–3.0 μm  region for a range of M stars. The observations show a good match with previous ground-based observations and with synthetic spectra based on the Partridge & Schwenke line list, although not with the SCAN line list. We have used a least-squared minimization technique to systematically find best-fitting parameters for the sample of stars. The temperatures that we find indicate a relatively hot temperature scale for M dwarfs. We consider that this could be a consequence of problems with the Partridge & Schwenke line list which leads to synthetic spectra predicting water bands that are too strong for a given temperature. Such problems need to be solved in the next generation of water vapour line lists, which will extend the calculation of water vapour to higher energy levels with the good convergence necessary for reliable modelling of hot water vapour. Then water bands can assume their natural role as the primary tool for the spectroscopic analysis of M stars.     

On the thorium absorption lines in the visible spectra of supergiant stars in the magellanic clouds

We present the results of the analysis of thorium absorption lines in the spectra of metal-deficient stars: the thorium-rich Galactic halo star HD 221170 and some supergiants in the Magellanic Clouds. For all the analyzed stars, the Th II lines were identified by comparing the synthetic and observed spectra. The Th II 6044.433 Å line and the weaker Th II 6619.943 Å line were identified in the spectra of red supergiants in the Magellanic Clouds.     

Near-ultraviolet observation of four bright Mn stars

Near-ultraviolet spectra, obtained with the ESRO TD-1A/S59 experiment, of the four Mn stars β Tau, γ Crv, α And, and μ Lep and six normal stars are compared. The normal stars show good agreement with synthetic spectra. The Mn stars have spectra which become hotter at shorter wavelengths. They also show strong Mnii lines and weak Mgii lines. A time-variation for Tiii λ 2828 was noted in γ Crv and α And.     

Shadows in S/NB-events of jovian decametric emission

Narrow-band (NB) events in dynamic spectra and their relation with short (S-) bursts are an unresolved enigma of the jovian decametric emission. This paper is focused on the S/NB-structure with timescales between 0.03 s and 0.3 s. It is shown that the characteristic dash-line appearance of such narrow-band radiation in the dynamic spectrum could be considered as a result of superposition of numerous shadows events. To reproduce such shadows, the concept of the modulator is proposed. The modulator is an activating or amplifying agent, which drifts in the dynamic spectrum toward lower frequencies to stimulate the generation process in the radio source. After the source interaction, the modulator is shielded; one cannot stimulate the emission afterwards. Hence, the S/NB-emission shadows a certain region of the spectrum. This ‘shadow effect’ regularizes the random S-bursts or NB-oscillations into realistic structures in the synthetic spectrum. The resemblance between the real and the synthetic spectra is shown with 2D-correlation analysis.     

Automated star–galaxy segregation using spectral and integrated band data for TAUVEX/ASTROSAT satellite data pipeline

We employ an Artificial Neural Network (ANN) based technique to develop a pipeline for automated segregation of stars from the galaxies to be observed by Tel-Aviv University Ultra-Violet Experiment (TAUVEX). We use synthetic spectra of stars from UVBLUE library and selected International Ultraviolet Explorer (IUE) low-resolution spectra for galaxies in the ultraviolet (UV) region from 1250 to 3220 Å as the training set and IUE low-resolution spectra for both the stars and the galaxies as the test set. All the data sets have been pre-processed to get band integrated fluxes so as to mimic the observations of the TAUVEX UV imager. We also perform the ANN based segregation scheme using the full length spectral features (which will also be useful for the ASTROSAT mission). Our results suggest that, in the case of the non-availability of full spectral features, the limited band integrated features can be used to segregate the two classes of objects; although the band data classification is less accurate than the full spectral data classification.