248 research outputs found
A new TiO line list
No full textA new line list for 9 electronic transitions of TiO (alpha, beta, gamma, gamma', delta, epsilon, phi, a-f, and E-B) is presented and made publicly available. It is the latest and much improved version of a suite of TiO line lists inaugurated in Plez et al</p
Observational constraints on the origin of the elements: III. Evidence for the dominant role of sub-Chandrasekhar SN Ia in the chemical evolution of Mn and Fe in the Galaxy
No full textThe abundance ratios of manganese to iron in late-type stars across a wide metallicity range place tight constraints on the astrophysical production sites of Fe-group elements. In this work, we investigate the chemical evolution of Mn in the Milky Way galaxy using high-resolution spectroscopic observations of stars in the Galactic disc and halo stars, as well as a sample of globular clusters. Our analysis shows that local thermodynamic equilibrium (LTE) leads to a strong imbalance in the ionisation equilibrium of Mn I and Mn II lines. Mn I produces systematically (up to 0.6 dex) lower abundances compared to the Mn II lines. Non-LTE (NLTE) radiative transfer satisfies the ionisation equilibrium across the entire metallicity range, of-3 ≲ [Fe/H] ≲-1, leading to consistent abundances from both ionisation stages of the element. We compare the NLTE abundances with Galactic Chemical Evolution models computed using different sources of type Ia and type II supernova (SN Ia and SN II) yields. We find that a good fit to our observations can be obtained by assuming that a significant (∼75%) fraction of SNe Ia stem from a sub-Chandrasekhar (sub-Mch) channel. While this fraction is larger than that found in earlier studies (∼50%), we note that we still require ∼25% near-Mch SNe Ia to obtain solar [Mn/Fe] at [Fe/H] = 0. Our new data also suggest higher SN II Mn yields at low metallicity than typically assumed in the literature
RED SUPERGIANTS AS COSMIC ABUNDANCE PROBES: The FIRST DIRECT METALLICITY DETERMINATION of NGC 4038 in the ANTENNAE
No full textWe present a direct determination of the stellar metallicity in the close pair galaxy NGC 4038 (D = 20 Mpc) based on the quantitative analysis of moderate-resolution KMOS/Very Large Telescope spectra of three super star clusters. The method adopted in our analysis has been developed and optimized to measure accurate metallicities from atomic lines in the J-band of single red supergiant (RSG) or RSG-dominated star clusters. Hence, our metallicity measurements are not affected by the biases and poorly understood systematics inherent to strong line H ii methods, which are routinely applied to massive data sets of galaxies. We find [Z] = +0.07 ± 0.03 and compare our measurements to H ii strong line calibrations. Our abundances and literature data suggest the presence of a flat metallicity gradient, which can be explained as redistribution of metal-rich gas following the strong interaction
Mobile Press-Register sleeve MP0099539
No full textUSA [University of South Alabama] board meeting - Plez B. Watson / (USA administration building
UBVJHK synthetic photometry of galactic O stars
No full textInternational audienceAims.The development of powerful infrared observational techniques enables the study of very extincted objects and young embedded star-forming regions. This is especially interesting in the context of massive stars that form and spend a non negligible fraction of their life still enshrouded in their parental molecular cloud. Spectrophotometric calibrations are thus necessary to constrain the physical properties of heavily extincted objects. Methods: Here, we derive UBVJHK magnitudes and bolometric corrections from a grid of atmosphere models for O stars. Bessel passbands are used. Bolometric corrections (BC) are derived as a function of Teff and are subsequently used to derive BC -spectral type (ST) and absolute magnitudes- ST relations. Results: Infrared magnitudes and, for the first time, bolometric corrections are given for the full range of spectral types and luminosity classes. Infrared colors are essentially constant, and (H-K)0 is 0.05 mag bluer than previously proposed. Optical calibrations are also provided and are similar to previous work, except for (B-V)0 which is found to be at minimum -0.28 for standard O stars, slightly higher (0.04 mag) than commonly accepted. Conclusions: We present a consistent set of photometric calibrations of optical and infrared magnitudes and bolometric corrections for Galactic O stars as a function of Teff and spectral type based on non-LTE atmosphere models including winds and line-blanketing
M-dwarf metallicities - A high-resolution spectroscopic study in the near infrared
No full text14 pages, 6 figures, 6 tables, accepted for publication in Astronomy and AstrophysicsInternational audienceThe relativley large spread in the derived metallicities ([Fe/H]) of M dwarfs shows that various approaches have not yet converged to consistency. The presence of strong molecular features, and incomplete line lists for the corresponding molecules have made metallicity determinations of M dwarfs difficult. Furthermore, the faint M dwarfs require long exposure times for a signal-to-noise ratio sufficient for a detailed spectroscopic abundance analysis. We present a high-resolution (R~50,000) spectroscopic study of a sample of eight single M dwarfs and three wide-binary systems observed in the infrared J-band. The absence of large molecular contributions allow for a precise continuum placement. We derive metallicities based on the best fit synthetic spectra to the observed spectra. To verify the accuracy of the applied atmospheric models and test our synthetic spectrum approach, three binary systems with a K-dwarf primary and an M-dwarf companion were observed and analysed along with the single M dwarfs. We obtain a good agreement between the metallicities derived for the primaries and secondaries of our test binaries and thereby confirm the reliability of our method of analysing M dwarfs. Our metallicities agree well with certain earlier determinations, and deviate from others. We conclude that spectroscopic abundance analysis in the J band is a reliable method for establishing the metallicity scale for M dwarfs. We recommend its application to a larger sample covering lower as well as higher metallicities. Further prospects of the method include abundance determinations for individual elements
The impact of winds on the spectral appearance of red supergiants
No full textThe rate at which mass is lost during the red supergiant (RSG) evolutionary stage may strongly influence how the star appears. Though there have been many studies discussing how RSGs appear in the mid- and far-infrared (IR) as a function of their mass-loss rate, to date, there have been no such investigations at optical and near-IR wavelengths. In a preliminary study, we construct model atmospheres for RSGs that include a wind, and use these models to compute synthetic spectra from the optical to the mid-IR. The inclusion of a wind has two important effects. First, higher mass-loss rates result in stronger absorption in the TiO bands, causing the star to appear as a later spectral type despite its effective temperature remaining constant. This explains the observed relation between spectral type, evolutionary stage, and mid-IR excess, as well as the mismatch between temperatures derived from the optical and IR. Secondly, the wind mimics many observed characteristics of a 'MOLsphere', potentially providing an explanation for the extended molecular zone inferred to exist around nearby RSGs. Thirdly, we show that wind fluctuations can explain the spectral variability of Betelgeuse during its recent dimming, without the need for dust
Analysis of the carbon-rich very metal-poor dwarf G77-61
No full textInternational audienceWe present an analysis of the carbon dwarf G77-61, a known binary, based on high resolution Keck spectra. G77-61 has a very-low metallicity, although not as extreme as what was previously conjectured. This star is very carbon-enhanced, the spectra showing very strong CH, CN, and C2 bands of both 13C and 12C isotopes. Atomic lines are sparse, and often blended, but we were able to derive abundances for Na, Mg, Ca, Cr, Mn, and Fe. Its [Fe/H] of -4.03 ± 0.1 places it among the lowest metallicity stars known, and its very high [C/Fe] = +2.6 , and [N/Fe] = +2.6 among the most C and N-rich metal-poor stars. The carbon isotopic ratio is 12C/13C = 5 ± 1. No overabundance of s- or r-process elements is detectable, but the upper limits that can be set on these overabundances are not very constraining
Data for: Cavity Ring-down UV spectroscopy of the C2Σ+-X2Π electronic transition of CH
No full textPGOPHER 10.0.505 [1] files for each of the vibronic bands (0-0, 1-1, 2-2) of the C-X system of CH. The constants for the ground X2Π state are fixed to those presented in Masseron et al [2]. Constants for the upper C2Σ+ state are floated. Files include assigned transition frequencies. [1] C.M. Western, J. Quant. Spectrosc. Radiat. Transf. 186 (2017) 221-242. doi:10.1016/J.JQSRT.2016.04.010.[2] T. Masseron, B. Plez, S. Van Eck, R. Colin, I. Daoutidis, M. Godefroid, P.-F. Coheur, P. Bernath, A. Jorissen, N. Christlieb, Astron. Astrophys. 571 (2014) A47. doi:10.1051/0004-6361/201423956
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