- ID:
- ivo://CDS.VizieR/J/ApJ/712/925
- Title:
- Transition circumstellar disks in Ophiuchus
- Short Name:
- J/ApJ/712/925
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained millimeter-wavelength photometry, high-resolution optical spectroscopy, and adaptive optics near-infrared imaging for a sample of 26 Spitzer-selected transition circumstellar disks. All of our targets are located in the Ophiuchus molecular cloud (d~125pc) and have spectral energy distributions (SEDs) suggesting the presence of inner opacity holes. We use these ground-based data to estimate the disk mass, multiplicity, and accretion rate for each object in our sample in order to investigate the mechanisms potentially responsible for their inner holes. We find that transition disks are a heterogeneous group of objects, with disk masses ranging from <0.6 to 40M_JUP_ and accretion rates ranging from <10^-11^ to 10^-7^M_{sun}_/yr, but most tend to have much lower masses and accretion rates than "full disks" (i.e., disks without opacity holes). Eight of our targets have stellar companions: six of them are binaries and the other two are triple systems. In four cases, the stellar companions are close enough to suspect they are responsible for the inferred inner holes. We find that nine of our 26 targets have low disk mass (<2.5M_JUP_) and negligible accretion (<10^-11^M_{sun}_/yr), and are thus consistent with photoevaporating (or photoevaporated) disks. Four of these nine non-accreting objects have fractional disk luminosities <10^-3^ and could already be in a debris disk stage. Seventeen of our transition disks are accreting. Thirteen of these accreting objects are consistent with grain growth. The remaining four accreting objects have SEDs suggesting the presence of sharp inner holes, and thus are excellent candidates for harboring giant planets.
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- ID:
- ivo://CDS.VizieR/J/A+A/622/A167
- Title:
- Transition data of E1 transitions for PII
- Short Name:
- J/A+A/622/A167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The main goal of this paper is to present accurate and extensive transition data for the PII ion. These data are useful in various astrophysical applications. The multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic configuration interaction (RCI) methods, which are implemented in the general-purpose relativistic atomic structure package GRASP2K, were used in the present work. In the RCI calculations the transverse-photon (Breit) interaction, the vacuum polarization, and the self-energy corrections were included. Energy spectra are presented for 48 even states of the 3s^2^3p^2^, 3s^2^3p{4p, 4f, 5p, 5f, 6p}, 3s3p^2^3d configurations, and for 58 odd states of the 3s3p^3^, 3s^2^3p{3d, 4s, 4d, 5s, 5d, 6s} configurations in the PII ion. Electric dipole (E1) transition data are computed between these states along with the corresponding lifetimes. The average uncertainty of the computed transition energies is between five and ten times smaller than the uncertainties from previous calculations. The computed lifetimes for the 3s^2^3p4s^3^P^o^ states are within the error bars of the most current experimental values.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A82
- Title:
- Transition data of E1 transitions for the CeIV
- Short Name:
- J/A+A/658/A82
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We present extensive energy level and transition data for the Ce IV spectrum. By providing accurate atomic data, we evaluate the impact of atomic data on the opacity in the neutron star merger ejecta. We performed energy spectra and transition data calculations using the GRASP2018 package, which is based on the multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods, and the HULLAC code, which is based on a parametric potential method. We present energy spectra calculated for the 225 levels for the Ce^3+^ ion. Energy levels are compared with recommended values from the NIST Atomic Spectra Database and other available works. The root-mean-square (rms) deviations obtained for the GRASP2018 energy levels of the 5p^6^nl configurations from the NIST data are 1270cm^-1^. The rms deviations for the HULLAC results from the NIST data are 5780cm^-1^. Furthermore, electric dipole (E1) transition data, line strengths, weighted oscillator strengths, and transition rates are computed between the above levels. The computed transition rates are compared with other theoretical computations. We also evaluate the accuracy of the wave functions and transition parameters by analyzing the dependencies of the line strength S on the gauge parameter G. The gauge dependency method also allows us to determine the transitions for which the ratio between the Babushkin and Coulomb gauges shows real agreement between forms and the transitions for which the agreement between both gauges is random. Using the GRASP2018 and HULLAC data, the opacities in the neutron star merger ejecta are also calculated. We find that the opacity of CeIV is higher than that presented by previous works, which is because of the higher completeness of our atomic data. Although the differences in the energy levels and transition probabilities cause different features in the opacity spectrum, the Planck mean opacities of both data sets agree within 20%.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A36
- Title:
- Transition disks around evolved stars
- Short Name:
- J/A+A/658/A36
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Post-AGB binaries are surrounded by massive disks of gas and dust that are similar to protoplanetary disks surrounding young stars. We assembled a catalog of all known Galactic post-AGB binaries with disks. We explore correlations between the different observables with the aim to learn more about potential disk-binary interactions. We compiled spectral energy distributions of 85 Galactic post-AGB binary systems. We built-up a color-color diagram to differentiate between the different disk morphologies traced by the characteristics of the infrared excess. We categorised different disk types and looked for correlations with other observational characteristics of these systems. 8 to 12% of our targets are surrounded by transition disks, i.e. disks having no or low near-infrared excesses. We find a strong link between these transition disks and the depletion of refractory elements seen on the surface of the post-AGB star. We interpret this correlation as evidence for the presence of a mechanism that stimulates the dust and gas separation within the disk and which also produces the transition disk structure. We propose that such a mechanism can be a giant planet carving a hole in the disk which traps the dust in the outer disk parts. We propose two disk evolutionary scenarios, depending on the presence of such a giant planet in the disk. We advocate that giant planets can successfully explain the correlation between the transition disks and the depletion of refractory materials observed in post-AGB binaries. If the planetary scenario is confirmed, disks around post-AGB binaries could be a unique laboratory to test planet-disk interactions and their influence on the late evolution of binary stars. Whether the planets are first or second generation also remains to be studied. We argue that these disks are the perfect place to study planet formation scenarios in an unprecedented parameter space.
- ID:
- ivo://CDS.VizieR/J/ApJ/749/79
- Title:
- Transition disks. II. Southern MoC
- Short Name:
- J/ApJ/749/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Transition disk objects are pre-main-sequence stars with little or no near-IR excess and significant far-IR excess, implying inner opacity holes in their disks. Here we present a multifrequency study of transition disk candidates located in Lupus I, III, IV, V, VI, Corona Australis, and Scorpius. Complementing the information provided by Spitzer with adaptive optics (AO) imaging (NaCo, VLT), submillimeter photometry (APEX), and echelle spectroscopy (Magellan, Du Pont Telescopes), we estimate the multiplicity, disk mass, and accretion rate for each object in our sample in order to identify the mechanism potentially responsible for its inner hole. We find that our transition disks show a rich diversity in their spectral energy distribution morphology, have disk masses ranging from <~1 to 10M_JUP_, and accretion rates ranging from <~10^-11^ to 10^-7.7^M_{sun}_/yr. Of the 17 bona fide transition disks in our sample, three, nine, three, and two objects are consistent with giant planet formation, grain growth, photoevaporation, and debris disks, respectively. Two disks could be circumbinary, which offers tidal truncation as an alternative origin of the inner hole.
22386. Transition disk survey
- ID:
- ivo://CDS.VizieR/J/A+A/592/A126
- Title:
- Transition disk survey
- Short Name:
- J/A+A/592/A126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Understanding disk evolution and dissipation is essential for studies of planet formation. Transition disks, i.e., disks with large dust cavities and gaps, are promising candidates of active evolution. About two dozen candidates, selected by their Spectral Energy Distribution (SED), have been confirmed to have dust cavities through millimeter interferometric imaging, but this sample is biased toward the brightest disks. The Spitzer surveys of nearby low-mass star-forming regions have resulted in more than 4000 young stellar objects (YSOs). Using color criteria, we selected a sample of ~150 candidates and an additional 40 candidates and known transition disks from the literature. The Spitzer data were complemented by new observations at longer wavelengths, including new JCMT and APEX submillimeter photometry, and WISE and Herschel-PACS mid- and far-infrared photometry. Furthermore, optical spectroscopy was obtained and stellar types were derived for 85% of the sample, including information from the literature. The SEDs were fit to a grid of RADMC-3D disk models with a limited number of parameters: disk mass, inner disk mass, scale height and flaring, and disk cavity radius, where the latter is the main parameter of interest. About 72% of our targets possibly have dust cavities based on the SED. The derived cavity sizes are consistent with imaging/modeling results in the literature, where available. Trends are found with the L_disk_ over L_*_ ratio and stellar mass and a possible connection with exoplanet orbital radii. A comparison with a previous study where color observables are used (Cieza et al., 2010, Cat. J/ApJ/712/925) reveals large overlap between their category of planet-forming disks and our transition disks with cavities. A large number of the new transition disk candidates are suitable for follow-up observations with ALMA.
- ID:
- ivo://CDS.VizieR/J/ApJ/855/123
- Title:
- Transition frequencies of ethanimine (CH_3_CHNH)
- Short Name:
- J/ApJ/855/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ethanimine, a possible precursor of amino acids, is considered an important prebiotic molecule and thus may play important roles in the formation of biological building blocks in the interstellar medium. In addition, its identification in Titan's atmosphere would be important for understanding the abiotic synthesis of organic species. An accurate computational characterization of the molecular structure, energetics, and spectroscopic properties of the E and Z isomers of ethanimine, CH_3_CHNH, has been carried out by means of a composite scheme based on coupled-cluster techniques, which also account for extrapolation to the complete basis-set limit and core-valence correlation correction, combined with density functional theory for the treatment of vibrational anharmonic effects. By combining the computational results with new millimeter-wave measurements up to 300GHz, the rotational spectrum of both isomers can be accurately predicted up to 500GHz. Furthermore, our computations allowed us to revise the infrared spectrum of both E- and Z-CH_3_CHNH, thus predicting all fundamental bands with high accuracy.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/141
- Title:
- Transition frequencies of MN and DMN
- Short Name:
- J/ApJ/805/141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-resolution pure rotational spectra of four alkylnaphthalenes were measured in the range of 6-15GHz using a molecular-beam Fourier-transform microwave spectrometer. Both a- and b-type transitions were observed for 1-methylnaphthalene (1-MN), 1,2-dimethylnaphthalene (1,2-DMN), and 1,3-dimethylnaphthalene (1,3-DMN); only a-type transitions were observed for 2-methylnaphthalene (2-MN). Geometry optimization and vibrational analysis calculations at the B3LYP/6-311++G(d,p) level of theory aided in the assignments of the spectra and the characterization of the structures. Differences between the experimental and predicted rotational constants are small, and they can be attributed in part to low-lying out-of-plane vibrations, which distort the alkylnaphthalenes out of their equilibrium geometries. Splittings of rotational lines due to methyl internal rotation were observed in the spectra of 2-MN, 1,2-DMN, and 1,3-DMN, and allowed for the determination of the barriers to methyl internal rotation, which are compared to values from density functional theory calculations. All four species are moderately polar, so they are candidate species for detection by radio astronomy, by targeting the transition frequencies reported here.
- ID:
- ivo://CDS.VizieR/J/A+A/416/383
- Title:
- Transition probabilities for Fe XVIII
- Short Name:
- J/A+A/416/383
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Energy levels and the corresponding transition probabilities as well oscillator strengths and line strengths for allowed (E1) and forbidden (E2, M1) transitions among the lowest 379 levels of fluorine-like Fe XVIII are presented. Calculations were performed using the multiconfigurational Dirac-Fock GRASP code.
- ID:
- ivo://CDS.VizieR/J/ApJS/169/120
- Title:
- Transition probabilities for HfII and Hf
- Short Name:
- J/ApJS/169/120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radiative lifetimes from laser-induced fluorescence measurements, accurate to ~+/-5%, are reported for 41 odd-parity levels of HfII (Z=72). The lifetimes are combined with branching fractions measured using Fourier transform spectrometry to determine transition probabilities for 150 lines of HfII. Approximately half of these new transition probabilities overlap with recent independent measurements using a similar approach. The two sets of measurements are found to be in good agreement for lines in common. Our new laboratory data are applied to refine the hafnium photospheric solar abundance and to determine hafnium abundances in 10 metal-poor giant stars with enhanced r-process abundances. For the Sun we derive log{epsilon}(Hf)=0.88+/-0.08 from four lines; the uncertainty is dominated by the weakness of the lines and their blending by other spectral features. Within the uncertainties of our analysis, the r-process-rich stars possess constant Hf/La and Hf/Eu abundance ratios, log{epsilon}(Hf/La)=-0.13+/-0.02 ({sigma}=0.06) and log{epsilon}(Hf/Eu)=+0.04+/-0.02 ({sigma}=0.06). The observed average stellar abundance ratio of Hf/Eu and La/Eu is larger than previous estimates of the solar system r-process-only value, suggesting a somewhat larger contribution from the r-process to the production of Hf and La. The newly determined Hf values could be employed as part of the chronometer pair, Th/Hf, to determine radioactive stellar ages.
