- ID:
- ivo://CDS.VizieR/J/ApJ/804/64
- Title:
- Empirical and model parameters of 183 M dwarfs
- Short Name:
- J/ApJ/804/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Precise and accurate parameters for late-type (late K and M) dwarf stars are important for characterization of any orbiting planets, but such determinations have been hampered by these stars' complex spectra and dissimilarity to the Sun. We exploit an empirically calibrated method to estimate spectroscopic effective temperature (T_eff_) and the Stefan-Boltzmann law to determine radii of 183 nearby K7-M7 single stars with a precision of 2%-5%. Our improved stellar parameters enable us to develop model-independent relations between T_eff_ or absolute magnitude and radius, as well as between color and T_eff_. The derived T_eff_-radius relation depends strongly on [Fe/H], as predicted by theory. The relation between absolute K_S_magnitude and radius can predict radii accurate to ~=3%. We derive bolometric corrections to the VR_C_I_C_grizJHK_S_ and Gaia passbands as a function of color, accurate to 1%-3%. We confront the reliability of predictions from Dartmouth stellar evolution models using a Markov chain Monte Carlo to find the values of unobservable model parameters (mass, age) that best reproduce the observed effective temperature and bolometric flux while satisfying constraints on distance and metallicity as Bayesian priors. With the inferred masses we derive a semi-empirical mass-absolute magnitude relation with a scatter of 2% in mass. The best-agreement models overpredict stellar T_eff_ values by an average of 2.2% and underpredict stellar radii by 4.6%, similar to differences with values from low-mass eclipsing binaries. These differences are not correlated with metallicity, mass, or indicators of activity, suggesting issues with the underlying model assumptions, e.g., opacities or convective mixing length.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/326/959
- Title:
- Empirical calibration of the near-IR Ca triplet
- Short Name:
- J/MNRAS/326/959
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- File table contains details of the new near-IR stellar library observed to calibrate the Ca II triplet. It includes the indices CaT*, CaT and PaT measured over the final spectra as well as their corresponding errors. The Henry Draper Catalogue number, other names (mainly HR and BD numbers), coordinates, spectral type, luminosity class, apparent magnitude and atmospheric parameters (as derived in Paper II; Cenarro et al., 2001MNRAS.326..981C) are also given.
- ID:
- ivo://CDS.VizieR/J/ApJ/740/60
- Title:
- Equivalent widths for NGC2419 and NGC7099 RGB stars
- Short Name:
- J/ApJ/740/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 2419 is a massive outer halo Galactic globular cluster (GC) whose stars have previously been shown to have somewhat peculiar abundance patterns. We have observed seven luminous giants that are members of NGC 2419 with Keck/HIRES at reasonable signal-to-noise ratio. One of these giants is very peculiar, with an extremely low [Mg/Fe] and high [K/Fe] but normal abundances of most other elements. The abundance pattern does not match the nucleosynthetic yields of any supernova model. The other six stars show abundance ratios typical of inner halo Galactic GCs, represented here by a sample of giants in the nearby GC M30. Although our measurements show that NGC 2419 is unusual in some respects, its bulk properties do not provide compelling evidence for a difference between inner and outer halo GCs.
- 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/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/ApJ/769/57
- Title:
- Equivalent widths of metal-poor stars
- Short Name:
- J/ApJ/769/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is well established that stellar effective temperatures determined from photometry and spectroscopy yield systematically different results. We describe a new, simple method to correct spectroscopically derived temperatures ("excitation temperatures") of metal-poor stars based on a literature sample with -3.3<[Fe/H]<-2.5. Excitation temperatures were determined from Fe I line abundances in high-resolution optical spectra in the wavelength range of ~3700-7000{AA}, although shorter wavelength ranges, up to 4750-6800{AA}, can also be employed, and compared with photometric literature temperatures. Our adjustment scheme increases the temperatures up to several hundred degrees for cool red giants, while leaving the near-main-sequence stars mostly unchanged. Hence, it brings the excitation temperatures in good agreement with photometrically derived values. The modified temperature also influences other stellar parameters, as the Fe I-Fe II ionization balance is simultaneously used to determine the surface gravity, while also forcing no abundance trend on the absorption line strengths to obtain the microturbulent velocity. As a result of increasing the temperature, the often too low gravities and too high microturbulent velocities in red giants become higher and lower, respectively. Our adjustment scheme thus continues to build on the advantage of deriving temperatures from spectroscopy alone, independent of reddening, while at the same time producing stellar chemical abundances that are more straightforwardly comparable to studies based on photometrically derived temperatures. Hence, our method may prove beneficial for comparing different studies in the literature as well as the many high-resolution stellar spectroscopic surveys that are or will be carried out in the next few years.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A165
- Title:
- Equivalent widths of 13 red giants in IC 4756
- Short Name:
- J/A+A/615/A165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Homogeneous investigations of red giant stars in open clusters contribute to studies of internal evolutionary mixing processes inside stars, which are reflected in abundances of mixing-sensitive chemical elements like carbon, nitrogen, and sodium, while {alpha}- and neutron-capture element abundances are useful in tracing the Galactic chemical evolution. The main aim of this study is a comprehensive chemical analysis of red giant stars in the open cluster IC 4756, including determinations of ^12^C/^13^C and C/N abundance ratios, and comparisons of the results with theoretical models of stellar and Galactic chemical evolution. We used a classical differential model atmosphere method to analyse high-resolution spectra obtained with the FEROS spectrograph on the 2.2m MPG/ESO Telescope. The carbon, nitrogen, and oxygen abundances, ^12^C/^13^C ratios, and neutron-capture element abundances were determined using synthetic spectra, and the main atmospheric parameters and abundances of other chemical elements were determined from equivalent widths of spectral lines.
- ID:
- ivo://CDS.VizieR/J/A+A/610/A66
- Title:
- Equivalent widths of 7 stars in NGC 6705
- Short Name:
- J/A+A/610/A66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar [{alpha}/Fe] abundance is sometimes used as a proxy for stellar age, following standard chemical evolution models for the Galaxy, as seen by different observational results. In this work we show that the Open Cluster NGC6705/M11 has a significant {alpha}-enhancement [{alpha}/Fe]>0.1dex, despite its young age (~300Myr), challenging the current paradigm.}{We use high resolution (R$>65,000$) high signal-to-noise (~70) spectra of 8 Red Clump stars, acquired within the OCCASO survey. We determine very accurate chemical abundances of several {alpha} elements, using an equivalent width methodology (Si, Ca and Ti), and spectral synthesis fits (Mg and O). We obtain [Si/Fe]=0.13+/-0.05, [Mg/Fe]=0.14+/-0.07, [O/Fe]=0.17+/-0.07, [Ca/Fe]=0.06+/-0.05 and [Ti/Fe]=0.03+/-0.03. Our results place these cluster within the group of young [{alpha}/Fe]-enhanced field stars recently found by several authors in the literature. The ages of our stars have an uncertainty of around 50Myr, much more precise than for field stars. By integrating the cluster's orbit in several non-axisymmetric Galactic potentials, we establish the M11's most likely birth radius to lie between 6.8-7.5kpc from the Galactic center, not far from its current position. With the robust Open Cluster age scale, our results prove that a moderate [{alpha}/Fe]-enhancement is no guarantee for a star to be old, and that not all {alpha}-enhanced stars can be explained with an evolved blue straggler scenario. Based on our orbit calculations, we further argue against a Galactic bar origin of M11.
