Search results for "Astronomical spectroscopy"
showing 10 items of 16 documents
Gaia -ESO Survey: Analysis of pre-main sequence stellar spectra
2015
This paper describes the analysis of UVES and GIRAFFE spectra acquired by the Gaia-ESO Public Spectroscopic Survey in the fields of young clusters whose population includes pre-main sequence (PMS) stars. Both methods that have been extensively used in the past and new ones developed in the contest of the Gaia-ESO survey enterprise are available and used. The internal precision of these quantities is estimated by inter-comparing the results obtained by such different methods, while the accuracy is estimated by comparison with independent external data, like effective temperature and surface gravity derived from angular diameter measurements, on a sample of benchmarks stars. Specific strategi…
MILES extended: Stellar population synthesis models from the optical to the infrared
2016
We present the first single-burst stellar population models which covers the optical and the infrared wavelength range between 3500 and 50000 Angstrom and which are exclusively based on empirical stellar spectra. To obtain these joint models, we combined the extended MILES models in the optical with our new infrared models that are based on the IRTF (Infrared Telescope Facility) library. The latter are available only for a limited range in terms of both age and metallicity. Our combined single-burst stellar population models were calculated for ages larger than 1 Gyr, for metallicities between [Fe/H] = -0.40 and 0.26, for initial mass functions of various types and slopes, and on the basis …
Relative Transition Probability Measurements for Prominent Infrared Spectral Lines of NI
2002
Applying a high-current wall-stabilized arc operated either in helium or in argon always with some admixtures of nitrogen, relative transition probabilities for more than 100 individual spectral lines (fine structure components) have been measured. The studied lines belong mainly to the 3p–3d and 3p–4s transition arrays. Ten lines of the measured set are intersystem transitions. Our data are compared with other experimental results (for about one half of the studied set there are available), with evaluated on the basis of the LS coupling scheme, with semiempirical data, and with recent CIV3 calculations. Some of our results are compared also with experimental data for the next member of the…
Correcting the effect of stellar spots on ARIEL transmission spectra
2020
The goal of this study is to assess the impact of the stellar spots on the extraction of the planetary transmission spectra observed by ARIEL. We develop a method to model the stellar spectrum of a star in the presence of spots by using the out-of-transit observations. It is based on a chi squared minimization procedure of the out-of-transit spectrum on a grid of stellar spectra with different sizes and temperatures of the spots. The approach allows us also to study the temporal evolution of the spots when comparing stellar spectra observed at different epochs. We also present a method to correct the transit depth variations due to non-occulted stellar spots and estimate the error we introd…
Temperature dependence of sodium and ionized calcium resonance lines perturbed by helium
2014
International audience; Traces of heavy metals in cool DZ white dwarf stars may be attributed to the accretion of circumstellar dust thought to originate from tidal disruption of rocky parent bodies. Spectra of such stars therefore provide a unique opportunity to study the composition of extrasolar planetary systems. The determination of metal abundances from stellar spectra depends on stellar atmospheric parameters and an accurate prior knowledge of the collision broadening of the line profiles by the most common constituents of the stellar atmosphere. For this purpose, we present theoretical absorption spectra of Na and Ca+ broadened by He for the conditions prevailing in cool white dwarf…
Spectral Evolution of Scorpio X‐1 along its Color‐Color Diagram
2007
We analyze a large collection of RXTE archive data of the bright X‐ray source Scorpius X‐1 in order to study the broadband spectral evolution of the source for different values of the inferred mass accretion rate by selecting energy spectra from its Color‐Color Diagram. We model the spectra with the combination of two absorbed components: a soft thermal component, which can be interpreted as thermal emission from an accretion disk, and a hybrid Comptonization component, which self‐consistently includes the Fe Kα fluorescence line and the Compton reflected continuum. The presence of hard emission in Scorpius X‐1 has been previously reported, however, without a clear relation with the accreti…
XMM-Newton observation of the classical T Tauri star SU Aurigae and the surrounding field
2007
Aims. We investigate the properties of the X-ray emitting plasma of the classical T Tauri star SU Aurigae and of other sources in the field of view. Methods. We use XMM-Newton to obtain a high-resolution RGS spectrum of SU Aur as well as EPIC imaging data and lowresolution spectra of the star and of other X-ray sources in the surrounding field. We reconstruct the emission measure distribution of SU Aur from the RGS spectrum using a line-based method, and we perform multi-temperature fits of the MOS spectra of the strongest sources both for the full observation and for selected time intervals to study their spectral variability. Results. The emission from SU Aur is highly variable, showing t…
The Sun as an X‐Ray Star. IV. The Contribution of Different Regions of the Corona to Its X‐Ray Spectrum
2001
We study X-ray-synthesized spectra of solar regions as templates to interpret analogous stellar spectra. We define three classes of coronal structures of different brightness, low (background quiet corona), medium (active regions), and high (active region cores), and determine their contribution to the solar X-ray emission measure versus temperature, EM(T), luminosity, and spectrum. This study defines the extent of the solar analogy quantitatively and accurately. To this end, we have selected a large sample of full-disk Yohkoh soft X-ray telescope observations taken between the maximum and the minimum of solar cycle 22, obtaining the contribution of each class to the whole Sun's EM(T). From…
Caii H and K spectroscopic observations in active binary systems
1990
We have performed high resolution spectroscopic observations of five active binary systems in the Caii H and K lines at La Palma Observatory. We present the absolute fluxes calculated at the surface of the stars and we discuss the spectral characteristics observed, presence of double emissions and phase variations.
Long-term variability of the Be/X-ray binary A 0535+26 -- I. Optical and UV spectroscopy
1998
The results of a 7-yr optical and UV spectroscopic study of the high-mass X-ray binary A 0535+26 are presented. It was found that throughout the period of the observations the line profile of Hα showed considerable variability. A correlation between the equivalent width of Hα and both V-band magnitude and (B−V) colour excess was observed, albeit with considerable scatter present in the data set. A giant X-ray flare in early 1994 was accompanied by a fading in optical and infrared photometric bands, and a reduction in the equivalent width of Hα. When the star was observed in 1994 September, it was found to have developed a double-peaked Hα profile, and further observations saw the V/R peak r…