- ID:
- ivo://CDS.VizieR/J/A+A/618/A16
- Title:
- A(Li) and 6Li/7Li 3D NLTE corrections
- Short Name:
- J/A+A/618/A16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The purpose of this work is to provide corrections for the lithium abundance, A(Li), and the ^6^Li/^7^Li ratio that can easily be applied to correct 1D LTE lithium abundances in G and F dwarf stars of approximately solar mass and metallicity for three-dimensional (3D) and non-LTE (NLTE) effects. The corrections for A(Li) and ^6^Li/^7^Li are computed using grids of 3D NLTE and 1D LTE synthetic lithium line profiles, generated from 3D hydro-dynamical CO5BOLD and 1D hydrostatic LHD model atmospheres, respectively. For comparative purposes, all calculations are performed for three different line lists representing the LiI 670.8nm spectral region. The 3D NLTE corrections are then approximated by analytical expressions as a function of the stellar parameters (Teff, logg, [Fe/H], vsini, A(Li), ^6^Li/^7^Li). The derived 3D NLTE corrections range between -0.01 and +0.11dex for A(Li), and between -4.9 and -0.4% for the ^6^Li/^7^Li ratio, depending on the adopted stellar parameters. Our findings show a general consistency with recent works on lithium abundance corrections. In the case of the ^6^Li/^7^Li ratio, our corrections are always negative, showing that 1D LTE analysis can significantly overestimate the presence of ^6^Li (up to 4.9 percentage points) in the atmospheres of solar-like dwarf stars. These results emphasize the importance of reliable 3D model atmospheres combined with NLTE line formation for deriving precise isotopic lithium abundances. Although 3D NLTE spectral synthesis implies an extensive computational effort, the results can be made accessible with parametric tools like the ones presented in this work.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/636/A67
- Title:
- ALMA maps of 6 sources of star forming regions
- Short Name:
- J/A+A/636/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As a building block for amino acids, formamide (NH_2_CHO) is an important molecule in astrobiology and astrochemistry, but its formation path in the interstellar medium is not understood well. We aim to find empirical evidence to support the chemical relationships of formamide to HNCO and H_2_CO. We examine high angular resolution (~0.2") Atacama Large Millimeter/submillimeter Array (ALMA) maps of six sources in three high-mass star-forming regions and compare the spatial extent, integrated emission peak position, and velocity structure of HNCO and H_2_CO line emission with that of NH_2_CHO by using moment maps. Through spectral modeling, we compare the abundances of these three species. In these sources, the emission peak separation and velocity dispersion of formamide emission is most often similar to HNCO emission, while the velocity structure is generally just as similar to H_2_CO and HNCO (within errors). From the spectral modeling, we see that the abundances between all three of our focus species are correlated, and the relationship between NH_2_CHO and HNCO reproduces the previously demonstrated abundance relationship. In this first interferometric study, which compares two potential parent species to NH_2_CHO, we find that all moment maps for HNCO are more similar to NH_2_CHO than H_2_CO in one of our six sources (G24 A1). For the other five sources, the relationship between NH_2_CHO, HNCO, and H_2_CO is unclear as the different moment maps for each source are not consistently more similar to one species as opposed to the other.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A167
- Title:
- (Al2O3)n, n=1-10, clusters data
- Short Name:
- J/A+A/658/A167
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Aluminium oxide (alumina; Al_2_O_3_) is a promising candidate as a primary dust condensate in the atmospheres of oxygen-rich evolved stars. Therefore, alumina 'seed' particles might trigger the onset of stellar dust formation and of stellar mass loss in the wind. However, the formation of alumina dust grains is not well understood. Aims. We aim to shed light on the initial steps of cosmic dust formation (i.e. nucleation) in oxygen-rich environments via a quantum- chemical bottom-up approach. Starting with an elemental gas-phase composition, we construct a detailed chemical-kinetic network that describes the formation and destruction of aluminium-bearing molecules and dust- forming (Al_2_O_3_)_n_ clusters up to the size of dimers (n=2) coagulating to tetramers (n=4). Intermediary species include the prevalent gas- phase molecules AlO and AlOH as well as Al_x_O_y_ clusters with x=1-5, y=1-6. The resulting extensive network is applied to two model stars, which represent a semi-regular variable and a Mira type, and to different circumstellar gas trajectories, including a non-pulsating outflow and a pulsating model. The growth of larger-sized (Al_2_O_3_)_n_ clusters with n=4-10 is described by the temperature-dependent Gibbs free energies of the most favourable structures (i.e. the global minima clusters) as derived from global optimisation techniques and calculated via density functional theory. We provide energies, bond characteristics, electrostatic properties, and vibrational spectra of the clusters as a function of size, n, and compare these to corundum, which corresponds to the crystalline bulk limit (n to infinity). The circumstellar aluminium gas-phase chemistry in oxygen- rich giants is primarily controlled by AlOH and AlO, which are tightly coupled by the reactions AlO+H_2_, AlO+H_2_O, and their reverse. Models of semi-regular variables show comparatively higher AlO abundances, as well as a later onset and a lower efficiency of alumina cluster formation when compared to Mira-like models. The Mira-like models exhibit an efficient cluster production that accounts for more than 90% of the available aluminium content, which is in agreement with the most recent ALMA observations. Chemical equilibrium calculations fail to predict both the alumina cluster formation and the abundance trends of AlO and AlOH in the asymptotic giant branch dust formation zone. Furthermore, we report the discovery of hitherto unreported global minimum candidates and low-energy isomers for cluster sizes n=7, 9, and 10. A homogeneous nucleation scenario, where Al2O3 monomers are successively added, is energetically viable. However, the formation of the Al2O3 monomer itself represents an energetic bottleneck. Therefore, we provide a bottom-up interpolation of the cluster characteristics towards the bulk limit by excluding the monomer, approximately following an n^(-1/3)^ dependence.
- ID:
- ivo://CDS.VizieR/J/ApJ/700/1173
- Title:
- Analysis of broad-line regions in AGNs
- Short Name:
- J/ApJ/700/1173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A two-component model for the broad-line region (BLR) of active galactic nuclei (AGNs) has been suggested for many years but not widely accepted. This model indicates that the broad line can be described with the superposition of two Gaussian components (very broad Gaussian component (VBGC) and intermediate Gaussian component (IMGC)) which are from two physically distinct regions, i.e., very broad line region (VBLR) and intermediate line region. We select a Sloan Digital Sky Survey sample to further confirm this model and give a detailed analysis of the geometry, density, and evolution of these two regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/865/153
- Title:
- Analysis of Fermi GRB data. IV. Spectral lags
- Short Name:
- J/ApJ/865/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The spectral evolution and spectral lag behavior of 92 bright pulses from 84 gamma-ray bursts observed by the Fermi Gamma-ray Burst Monitor (GBM) telescope are studied. These pulses can be classified into hard-to-soft pulses (H2S; 64/92), H2S-dominated-tracking pulses (21/92), and other tracking pulses (7/92). We focus on the relationship between spectral evolution and spectral lags of H2S and H2S-dominated-tracking pulses. The main trend of spectral evolution (lag behavior) is estimated with logE_p_{propto}k_E_log(t+t_0_) (^{tau}{propto}k_^{tau}logE), where E_p_ is the peak photon energy in the radiation spectrum, t+t_0_ is the observer time relative to the beginning of pulse -t0, and ^{tau} is the spectral lag of photons with energy E with respect to the energy band 8-25keV. For H2S and H2S-dominated-tracking pulses, a weak correlation between k_^{tau}/W and kE is found, where W is the pulse width. We also study the spectral lag behavior with peak time t_pE_ of pulses for 30 well-shaped pulses and estimate the main trend of the spectral lag behavior with logt_pE_{propto}k_tp_logE. It is found that k_tp_ is correlated with kE. We perform simulations under a phenomenological model of spectral evolution, and find that these correlations are reproduced. We then conclude that spectral lags are closely related to spectral evolution within the pulse. The most natural explanation of these observations is that the emission is from the electrons in the same fluid unit at an emission site moving away from the central engine, as expected in the models invoking magnetic dissipation in a moderately high-{sigma} outflow.
- ID:
- ivo://CDS.VizieR/J/AJ/143/39
- Title:
- Analysis of hot Jupiters in Kepler Q2
- Short Name:
- J/AJ/143/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we present the results of searching the Kepler Q2 public data set for the secondary eclipses of 76 hot Jupiter planet candidates from the list of 1235 candidates published by Borucki et al., 2011, Cat. J/ApJ/736/19. This search has been performed by modeling both the Kepler pre-search data conditioned light curves and new light curves produced via our own photometric pipeline. We derive new stellar and planetary parameters for each system, while calculating robust errors for both. We find 16 systems with 1{sigma}-2{sigma}, 14 systems with 2{sigma}-3{sigma}, and 6 systems with >3{sigma} confidence level secondary eclipse detections in at least one light curve produced via the Kepler pre-search data conditioned light curve or our own pipeline; however, results can vary depending on the light curve modeled and whether eccentricity is allowed to vary or not. We estimate false alarm probabilities of 31%, 10%, and 6% for the 1{sigma}-2{sigma}, 2{sigma}-3{sigma}, and >3{sigma} confidence intervals, respectively.
- ID:
- ivo://CDS.VizieR/J/AJ/154/269
- Title:
- A new photo-z method for quasars in Stripe 82
- Short Name:
- J/AJ/154/269
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new algorithm to estimate quasar photometric redshifts (photo-zs), by considering the asymmetries in the relative flux distributions of quasars. The relative flux models are built with multivariate Skew-t distributions in the multidimensional space of relative fluxes as a function of redshift and magnitude. For 151392 quasars in the SDSS, we achieve a photo-z accuracy, defined as the fraction of quasars with the difference between the photo-z z_p_ and the spectroscopic redshift z_s_, |{Delta}_z_|=|z_s_-z_p_|/(1+z_s_) within 0.1, of 74%. Combining the WISE W1 and W2 infrared data with the SDSS data, the photo-z accuracy is enhanced to 87%. Using the Pan-STARRS1 or DECaLS photometry with WISE W1 and W2 data, the photo-z accuracies are 79% and 72%, respectively. The prior probabilities as a function of magnitude for quasars, stars, and galaxies are calculated, respectively, based on (1) the quasar luminosity function, (2) the Milky Way synthetic simulation with the Besancon model, and (3) the Bayesian Galaxy Photometric Redshift estimation. The relative fluxes of stars are obtained with the Padova isochrones, and the relative fluxes of galaxies are modeled through galaxy templates. We test our classification method to select quasars using the DECaLS g, r, z, and WISE W1 and W2 photometry. The quasar selection completeness is higher than 70% for a wide redshift range 0.5<z<4.5, and a wide magnitude range 18<r<21.5 mag. Our photo-z regression and classification method has the potential to extend to future surveys. The photo-z code will be publicly available.
- ID:
- ivo://CDS.VizieR/J/AJ/157/242
- Title:
- An updated study of potential targets for Ariel
- Short Name:
- J/AJ/157/242
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ariel has been selected as ESA's M4 mission for launch in 2028 and is designed for the characterization of a large and diverse population of exoplanetary atmospheres to provide insights into planetary formation and evolution within our Galaxy. Here we present a study of Ariel's capability to observe currently known exoplanets and predicted Transiting Exoplanet Survey Satellite (TESS) discoveries. We use the Ariel radiometric model (ArielRad) to simulate the instrument performance and find that ~2000 of these planets have atmospheric signals which could be characterized by Ariel. This list of potential planets contains a diverse range of planetary and stellar parameters. From these we select an example mission reference sample (MRS), comprised of 1000 diverse planets to be completed within the primary mission life, which is consistent with previous studies. We also explore the mission capability to perform an in-depth survey into the atmospheres of smaller planets, which may be enriched or secondary. Earth-sized planets and super-Earths with atmospheres heavier than H/He will be more challenging to observe spectroscopically. However, by studying the time required to observe ~110 Earth-sized/super-Earths, we find that Ariel could have substantial capability for providing in-depth observations of smaller planets. Trade-offs between the number and type of planets observed will form a key part of the selection process and this list of planets will continually evolve with new exoplanet discoveries replacing predicted detections. The Ariel target list will be constantly updated and the MRS re-selected to ensure maximum diversity in the population of planets studied during the primary mission life.
- ID:
- ivo://CDS.VizieR/J/ApJ/888/43
- Title:
- APOGEE-Kepler Cool Dwarf star ages determination
- Short Name:
- J/ApJ/888/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use models of stellar angular momentum evolution to determine ages for ~500 stars in the APOGEE-Kepler Cool Dwarfs sample. We focus on lower-main-sequence stars, where other age-dating tools become ineffective. Our age distributions are compared to those derived from asteroseismic and giant samples and solar analogs. We are able to recover gyrochronological ages for old, lower-main-sequence stars, a remarkable improvement over prior work in hotter stars. Under our model assumptions, our ages have a median relative uncertainty of 14%, comparable to the age precision inferred for more massive stars using traditional methods. We investigate trends of Galactic {alpha}-enhancement with age, finding evidence of a detection threshold between the age of the oldest {alpha}-poor stars and that of the bulk {alpha}-rich population. We argue that gyrochronology is an effective tool reaching ages of 10-12Gyr in K and early M dwarfs. Finally, we present the first effort to quantify the impact of detailed abundance patterns on rotational evolution. We estimate a ~15% bias in age for cool, {alpha}-enhanced (+0.4dex) stars when standard solar-abundance-pattern rotational models are used for age inference, rather than models that appropriately account for {alpha}-enrichment.
- ID:
- ivo://CDS.VizieR/J/AJ/132/1851
- Title:
- Arecibo obs. of formaldehyde in L1551
- Short Name:
- J/AJ/132/1851
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report observations of the formaldehyde (H_2_CO) 6cm (4.8GHz) line toward L1551. The observations were conducted with the Arecibo Telescope (beam FWHP~1') to verify the tentative detection of H_2_CO thermal emission reported by Duncan and collaborators in 1987MNRAS.224..721D. The H_2_CO emission lines were expected to be present with a signal-to-noise ratio of >~10 in our spectra. However, we did not detect H_2_CO emission; i.e., our data rule out their tentative detection. The absence of H_2_CO emission is also confirmed by the fact that the H_2_CO line profiles at the two positions of expected emission are well fitted by a single absorption component (accounting for the hyperfine structure of the line) in one of the positions and by a single absorption line plus a red-wing absorption component in the second position. The Orion BN/KL region remains the only H_2_CO 6cm thermal emitter known. Our observations also demonstrate that the H_2_CO 6cm absorption line traces not only the quiescent molecular cloud but also the kinematics associated with the star formation process in L1551-IRS5.
