We present 2um (K band) spectra of 180 well-studied, optically visible, luminous stars. Most of the stars are of OB spectral type, but we have also included a number of Oe and Be stars, OBN and OBC stars, cool hypergiant stars, and high-mass X-ray binary stars. Our aim in studying normal OB stars is to develop an empirical relationship between 2um spectral features of these massive stars and their stellar temperature and luminosity. We find the system of lines between 2.0 and 2.2um is particulary good for differentiating the early- and mid-O type stars. In the late-O and early-B stars, differentiation becomes more difficult, as the features show only moderate changes. We have developed a spectral classification system for the K band to be used to estimate effective temperatures of O and early-B stars. We demonstrate that K-band spectroscopy is superior in estimating the temperature of hot, luminous stars than the traditional methods of using infrared or even optical photometric colors alone. The only requirements are that adequate resolution (R>1000) and signal-to-noise (S/N~70) be achieved. With our classification system, stars behind large amounts of visible extinction, such as young, heavily reddened H II regions throughout our Galaxy, may be identified and studied for the first time through 2um spectroscopy. Emission lines are commonly seen in the K-band spectra of supergiant stars, however, the OBN supergiants, which have a higher ratio of some processed materials at their surface, may be more likely to show line emission, especially the He I singlet transition at 2.058um. This has led us to propose an evolutionary scenario for some of the Galactic center He I emission-line stars, which evokes rotational mixing (Maeder 1987A&A...178..159M; Langer 1992A&A...265L..17L) to explain both the strong line emission and high luminosity of these mysterious sources. We have compared our spectroscopic database with the most recent stellar atmosphere models. We are encouraged by the good match between the model line profiles at 2um of Schaerer et al. (1996A&A...312..475S) and those observed in OB stars. Finally, we include a thorough discussion of the observational and reduction methods employed to obtain the spectra shown in this atlas for the benefit of those wishing to obtain similar, classification-quality, near-infrared spectra.
We present a compilation of spectra of 101 Seyfert galaxies obtained with the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS), covering the UV and/or optical spectral range. Information on all the available spectra have been collected in a Mastertable, which is a very useful tool for anyone interested in a quick glance at the existent STIS spectra for Seyfert galaxies in the HST archive, and it can be recovered electronically. Nuclear spectra of the galaxies have been extracted in windows of 0.2" for an optimized sampling (as this is the slit width in most cases) and combined in order to improve the signal-to-noise ratio and provide the widest possible wavelength coverage. These combined spectra are also available electronically, at http://www.if.ufrgs.br/~pat/atlas.htm .
This Atlas illustrates the behavior of stars of all spectral types in the near infrared 8400-8800 Angstrom spectral region with a resolution of about one Angstrom. The spectra have been obtained at the Observatoire de Haute-Provence at a dispersion of 33{AA}/mm. A total of 130 spectra (76 of early-type stars published in Paper I, and 54 of late-type stars published in Paper II) are available. They cover the spectral range O to M and different luminosity classes. The Atlas includes also spectra of stars with spectral peculiarities: 19 from Paper I and 11 from Paper II.
A library of 711 cool star synthetic spectra in the wavelength range 485-540nm is presented. The coverage in the parameter space span in surface gravity from 1.0 to 5.0dex at a step of 0.5dex. The range in effective temperature covers from 4000 to 6000K at a step of 250K plus the spectra for 7000 and 8000K. The global chemical compositions are [M/H]=-1.0, -0.5, 0.0, +0.1, +0.2, +0.3 and +0.5. The adopted value of microturbulent velocity is 2km/s but for two sets of nine spectra each. All the spectra are computed at a resolving power =250,000. For each wavelength point the continuum and line blanketed absolute fluxes per unit frequency are given.
Parameters and abundances for 451 stars of spectral types F, G, and K of luminosity classes I and II have been derived. Absolute magnitudes and E(B-V) have been derived for the warmer stars in order to investigate the galactic abundance gradient. The value found here: d[Fe/H]/dR~-0.06dex/kpc, agrees well with previous determinations. Stellar evolution indicators have also been investigated with the derived C/O ratios indicating that standard CN processing has been operating. Perhaps the most surprising result found in these supposedly relatively young intermediate-mass stars is that both [O/Fe] and [C/Fe] show a correlation with [Fe/H] much the same as found in older populations. While the stars were selected based on luminosity class, there does exist a significant [Fe/H] range in the sample. The likely explanation of this is that there is a significant range in age in the sample; that is, some of the sample are low-mass red-giant stars with types that place them within the selection criteria.
We report new metallicities for stars of Galactic globular cluster M4 using the largest number of stars ever observed at high spectral resolution in any cluster. We analyzed 7250 spectra for 2771 cluster stars gathered with the Very Large Telescope (VLT) FLAMES+GIRAFFE spectrograph at VLT. These medium-resolution spectra cover a small wavelength range, and often have very low signal-to-noise ratios. We approached this data set by reconsidering the whole method of abundance analysis of large stellar samples from beginning to end. We developed a new algorithm that automatically determines the atmospheric parameters of a star. Nearly all of the data preparation steps for spectroscopic analyses are processed on the syntheses, not the observed spectra. For 322 red giant branch (RGB) stars with V<=14.7, we obtain a nearly constant metallicity, <[Fe/H]>=-1.07 ({sigma}=0.02). No difference in the metallicity at the level of 0.01 dex is observed between the two RGB sequences identified by Monelli et al. (2013MNRAS.431.2126M). For 1869 subgiant and main-sequence stars with V>14.7, we obtain <[Fe/H]>=-1.16 ({sigma}=0.09) after fixing the microturbulent velocity. These values are consistent with previous studies that have performed detailed analyses of brighter RGB stars at higher spectroscopic resolution and wavelength coverage. It is not clear if the small mean metallicity difference between brighter and fainter M4 members is real or is the result of the low signal-to-noise characteristics of the fainter stars. The strength of our approach is shown by recovering a metallicity close to a single value for more than 2000 stars, using a data set that is non-optimal for atmospheric analyses. This technique is particularly suitable for noisy data taken in difficult observing conditions.
We are conducting a precision radial velocity study of a sample of 164 nearby giant stars in the southern hemisphere. In this work we present the spectroscopic atmospheric parameters (Teff, logg , vmic and [Fe/H]) for all of our targets. By comparing the position on the HR diagram with stellar evolutionary tracks, we derived the mass, radius and evolutionary status for every star in our sample. In addition, rotational velocities are also measured.
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