- ID:
- ivo://CDS.VizieR/J/A+A/549/A129
- Title:
- Equivalent widths of cool stars
- Short Name:
- J/A+A/549/A129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The near-infrared (NIR) wavelength range offers some unique spectral features, and it is less prone to the extinction than the optical one. Recently, the first flux calibrated NIR library of cool stars from the NASA Infrared Telescope Facility (IRTF) have become available, and it has not been fully exploited yet. We want to develop spectroscopic diagnostics for stellar physical parameters based on features in the wavelength range 1-5um. In this work we test the technique in the I and K bands. The study of the Y, J, H, and L bands will be presented in the following paper. An objective method for semi-empirical definition of spectral features sensitive to various physical parameters is applied to the spectra. It is based on sensitivity map - i.e., derivative of the flux in the spectra with respect to the stellar parameters at a fixed wavelength. New optimized indices are defined and their equivalent widths (EWs) are measured.
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- ID:
- ivo://CDS.VizieR/J/A+A/555/A25
- Title:
- Equivalent widths of DIBs
- Short Name:
- J/A+A/555/A25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar spectroscopic surveys may bring useful statistical information on the links between diffuse interstellar bands (DIBs) and the interstellar environment. DIB databases can also be used as a complementary tool for locating interstellar (IS) clouds. Our goal is to develop fully automated methods of DIB measurements to be applied to extensive data from stellar surveys. We present a method that is appropriate for early-type nearby stars, along with its application to high-resolution spectra of ~130 targets recorded with the ESO FEROS spectrograph and comparisons with other determinations. Using a DIB average profile deduced from the most reddened stars, we performed an automated fitting of a combination of a smooth stellar continuum, the DIB profile, and, when necessary, a synthetic telluric transmission.
- ID:
- ivo://CDS.VizieR/J/ApJ/850/194
- Title:
- Equivalent widths of 8 DIBs for 186 O & B stars
- Short Name:
- J/ApJ/850/194
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the behavior of eight diffuse interstellar bands (DIBs) in different interstellar environments, as characterized by the fraction of hydrogen in molecular form (f_H2_), with comparisons to the corresponding behavior of various known atomic and molecular species. The equivalent widths of the five "normal" DIBs ({lambda}{lambda}5780.5, 5797.1, 6196.0, 6283.8, and 6613.6), normalized to E_B-V_, show a "lambda-shaped" behavior: they increase at low f_H2_, peak at f_H2_~0.3, and then decrease. The similarly normalized column densities of Ca, Ca+, Ti+, and CH+ also decline for f_H2_>0.3. In contrast, the normalized column densities of Na, K, CH, CN, and CO increase monotonically with fH2, and the trends exhibited by the three C_2_ DIBs ({lambda}{lambda}4726.8, 4963.9, and 4984.8) lie between those two general behaviors. These trends with f_H2_ are accompanied by cosmic scatter, the dispersion at any given f_H2_ being significantly larger than the individual errors of measurement. The lambda-shaped trends suggest the balance between creation and destruction of the DIB carriers differs dramatically between diffuse atomic and diffuse molecular clouds; additional processes aside from ionization and shielding are needed to explain those observed trends. Except for several special cases, the highest W{lambda}(5780)/W{lambda}(5797) ratios, characterizing the so-called "sigma-zeta effect," occur only at f_H2_<0.2. We propose a sequence of DIBs based on trends in their pair-wise strength ratios with increasing f_H2_. In order of increasing environmental density, we find the {lambda}6283.8 and {lambda}5780.5 DIBs, the {lambda}6196.0 DIB, the {lambda}6613.6 DIB, the {lambda}5797.1 DIB, and the C_2_ DIBs.
- ID:
- ivo://CDS.VizieR/J/AJ/130/652
- Title:
- Equivalent widths of 4 giants in Be22 and Be66
- Short Name:
- J/AJ/130/652
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on high-resolution spectroscopy of four giant stars in the Galactic old open clusters Berkeley 22 and Berkeley 66 obtained with HIRES at the Keck telescope.
- ID:
- ivo://CDS.VizieR/J/ApJ/887/91
- Title:
- Equivalent widths of giants in the GC NGC3201
- Short Name:
- J/ApJ/887/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hubble Space Telescope (HST) UV Legacy Survey of Galactic Globular Clusters (GCs) has investigated multiple stellar populations by means of the "chromosome map" (ChM) diagnostic tool that maximizes the separation between stars with different chemical compositions. One of the most challenging features revealed by ChM analysis is the apparent inhomogeneity among stars belonging to the first population, a phenomenon largely attributed to He variations. However, this explanation is not supported by uniformity in the p-capture elements of these stars. The HST survey has revealed that the GC NGC 3201 shows exceptionally wide coverage in the {Delta}_F275W,F814W_ parameter of the ChM. We present a chemical abundance analysis of 24 elements in 18 giants belonging to the first population of this GC and having a wide range in {Delta}_F275W,F814W_. As far as the p-capture elements are concerned, the chemical abundances are typical of first-generation (1G) stars, as expected from the location of our targets in the ChM. Based on radial velocities and chemical abundance arguments, we find that the three stars with the lowest {Delta}_F275W,F814W_ values are binary candidates. This suggests that at least those stars could be explained with binarity. These results are consistent with evidence inferred from multiband photometry that evolved blue stragglers (BSs) populate the bluest part of the 1G sequence in the ChM. The remaining 15 spectroscopic targets show a small range in the overall metallicity by ~0.10dex, with stars at higher {Delta}_F275W,F814W_ values having higher absolute abundances. We suggest that a small variation in metals and binarity governs the color spread of the 1G in the ChM and that evolved BSs contribute to the bluest tail of the 1G sequence.
- ID:
- ivo://CDS.VizieR/J/A+A/435/657
- Title:
- Equivalent widths of 5 giants in 47 Tuc
- Short Name:
- J/A+A/435/657
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High resolution spectra of 5 giants, including a horizontal branch star, of the metal-rich globular cluster 47 Tucanae were obtained with the UVES spectrograph at the 8m VLT UT2-Kueyen telescope. The atmospheric parameters (Teff, logg, [Fe/H], vt) were derived from VIJK photometry and spectroscopic data based on Fe I and Fe II lines.
- ID:
- ivo://CDS.VizieR/J/A+A/501/553
- Title:
- Equivalent widths of IC 2602 & IC 2391 stars
- Short Name:
- J/A+A/501/553
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic open clusters have been long recognized as one of the best tools to investigate the chemical content of Galactic disk and its time evolution. In the last decade, many efforts have been directed to chemically characterize the old and intermediate age population; surprisingly, the chemical content of the younger and close counterpart remains largely undetermined. In this paper we present the abundance analysis of a sample of 15 G/K members of the young pre-main sequence clusters IC 2602 and IC 2391. Along with IC 4665, these are the first pre-main sequence clusters for which a detailed abundance determination has been carried out so far.
- ID:
- ivo://CDS.VizieR/J/ApJ/798/110
- Title:
- Equivalent widths of LAMOST metal-poor stars
- Short Name:
- J/ApJ/798/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on early results from a pilot program searching for metal-poor stars with LAMOST and follow-up high-resolution observation acquired with the MIKE spectrograph attached to the Magellan II telescope. We performed detailed abundance analysis for eight objects with iron abundances [Fe/H]<-2.0, including five extremely metal-poor (EMP; [Fe/H]<-3.0) stars with two having [Fe/H]<-3.5. Among these objects, three are newly discovered EMP stars, one of which is confirmed for the first time with high-resolution spectral observations. Three program stars are regarded as carbon-enhanced metal-poor (CEMP) stars, including two stars with no enhancement in their neutron-capture elements, which thus possibly belong to the class of CEMP-no stars; one of these objects also exhibits significant enhancement in nitrogen, and is thus a potential carbon and nitrogen-enhanced metal-poor star. The [X/Fe] ratios of the sample stars generally agree with those reported in the literature for other metal-poor stars in the same [Fe/H] range. We also compared the abundance patterns of individual program stars with the average abundance pattern of metal-poor stars and find only one chemically peculiar object with abundances of at least two elements (other than C and N) showing deviations larger than 0.5 dex. The distribution of [Sr/Ba] versus [Ba/H] agrees that an additional nucleosynthesis mechanism is needed aside from a single r-process. Two program stars with extremely low abundances of Sr and Ba support the prospect that both main and weak r-processes may have operated during the early phase of Galactic chemical evolution. The distribution of [C/N] shows that there are two groups of carbon-normal giants with different degrees of mixing. However, it is difficult to explain the observed behavior of the [C/N] of the nitrogen-enhanced unevolved stars based on current data.
- ID:
- ivo://CDS.VizieR/J/A+A/503/545
- Title:
- Equivalent widths of Li, Na, Fe, Ca in NGC 6397
- Short Name:
- J/A+A/503/545
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To alleviate the discrepancy between the prediction of the primordial lithium abundance in the universe and the abundances observed in Pop II dwarfs and subgiant stars, it has been suggested that the stars observable today have undergone photospheric depletion of lithium. To identify the cause of such depletion, it is important to accurately establish the behaviour of lithium abundance with effective temperature and evolutionary phase. Stars in globular clusters are ideal objects for such abundance analysis, as relative stellar parameters can be precisely determined. We conduct a homogeneous analysis of a very large sample of stars in the metal-poor globular cluster NGC 6397, covering well all evolutionary phases from below the main sequence turn-off to high up the red giant branch. Non-LTE Li abundances or abundance upper limits are obtained for all stars, and for a size-able sub-set of the targets also Na abundances are obtained. The sodium abundances are used to distinguish stars formed out of pristine material from stars formed out of material affected by pollution from a previous generation of more massive stars. The dwarfs, turn-off, and early subgiant stars in our sample form a thin abundance plateau, disrupted in the middle of the subgiant branch by the lithium dilution caused by the first dredge-up. A second steep abundance drop is seen at the luminosity of the red giant branch bump. The turn-off stars are more lithium-poor, by up to 0.1dex, than subgiants that have not yet undergone dredge-up. In addition, hotter dwarfs are slightly more lithium-poor than cooler dwarfs, which may be a signature of the so-called Li dip in the cluster, commonly seen among PopI stars. The feature is however weak. A considerably large spread in Na abundance confirms that NGC6397 has suffered from intra-cluster pollution in its infancy and a limited number of Na-enhanced and Li-deficient stars strongly contribute to form a significant anti-correlation between the abundances of Na and Li. It is nevertheless seen that lithium abundances are unaffected by relatively high degrees of pollution. Lithium abundance trends with effective temperature and stellar luminosity are compared to predictions from stellar structure models including atomic diffusion and ad-hoc turbulence below the convection zone. We confirm previous findings that some turbulence, with strict limits to its efficiency, is necessary to explain the observations.
- ID:
- ivo://CDS.VizieR/J/A+A/425/671
- Title:
- Equivalent widths of 10 metal-poor halo stars
- Short Name:
- J/A+A/425/671
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We presented the observed information of ten metal-poor halo stars with the metallicity range -2.3<[Fe/H]< -1.4 and derived their stellar parameters, acquired some elemental abundances relative to iron and discussed the relation between the abundance ratio and the metallicity. The stars were observed using the 6m telescope of the Special Astrophysical Observatory with the ECHELLE spectrometer PFES equipped with the CCD (1040x1160 pixels, pixel size 16x16{mu}m). The spectral wavelength coverage is of 430-798nm with the resolving power of 15000 and the signal-to-noise ratio is about 200. It was found that oxygen abundances are nearly constant at a level of 0.6dex for our metal-poor halo stars when the non-LTE correction is considered. The alpha-elements (Mg, Si, Ca and Ti) are overabundant relative to Fe and decrease with increasing metallicity. We also obtained a significant underabundant non-LTE [Na/Fe] ratio from NaI D lines which have large deviation from LTE assumption. Scandium is marginally overabundant with respect to iron and tends to decrease with increasing metallicity like the alpha-elements. Nearly solar value of [Cr/Fe] ratio and underabundant [Mn/Fe] ratio are obtained.