- ID:
- ivo://CDS.VizieR/J/A+A/579/A20
- Title:
- Circumstellar debris discs
- Short Name:
- J/A+A/579/A20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Tentative correlations between the presence of dusty circumstellar debris discs and low-mass planets have recently been presented. In parallel, detailed chemical abundance studies have reported different trends between samples of planet and non-planet hosts. Whether these chemical differences are indeed related to the presence of planets is still strongly debated. We aim to test whether solar-type stars with debris discs show any chemical peculiarity that could be related to the planet formation process. We determine in a homogeneous way the metallicity, [Fe/H], and abundances of individual elements of a sample of 251 stars including stars with known debris discs, stars harbouring simultaneously debris discs and planets, stars hosting exclusively planets, and a comparison sample of stars without known discs or planets. High-resolution echelle spectra (R~57000) from 2-3m class telescopes are used. Our methodology includes the calculation of the fundamental stellar parameters (T_eff_, logg, microturbulent velocity, and metallicity) by applying the iron ionisation and equilibrium conditions to several isolated Fe i and Fe ii lines, as well as individual abundances of C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn.
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- ID:
- ivo://CDS.VizieR/J/A+A/580/A131
- Title:
- Circumstellar-interacting supernovae
- Short Name:
- J/A+A/580/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Some circumstellar-interacting (CSI) supernovae (SNe) are produced by the explosions of massive stars that have lost mass shortly before the SN explosion. There is evidence that the precursors of some SNe IIn were luminous blue variable (LBV) stars. For a small number of CSI SNe, outbursts have been observed before the SN explosion. Eruptive events of massive stars are named SN impostors (SN IMs) and whether they herald a forthcoming SN or not is still unclear. The large variety of observational properties of CSI SNe suggests the existence of other progenitors, such as red supergiant (RSG) stars with superwinds. Furthermore, the role of metallicity in the mass loss of CSI SN progenitors is still largely unexplored. Our goal is to gain insight into the nature of the progenitor stars of CSI SNe by studying their environments, in particular the metallicity at their locations. We obtain metallicity measurements at the location of 60 transients (including SNe IIn, SNe Ibn, and SN IMs) via emission-line diagnostic on optical spectra obtained at the Nordic Optical Telescope and through public archives. Metallicity values from the literature complement our sample. We compare the metallicity distributions among the different CSI SN subtypes, and to those of other core-collapse SN types. We also search for possible correlations between metallicity and CSI SN observational properties. We find that SN IMs tend to occur in environments with lower metallicity than those of SNe IIn. Among SNe IIn, SN IIn-L(1998S-like) SNe show higher metallicities, similar to those of SNe IIL/P, whereas long-lasting SNe IIn (1988Z-like) show lower metallicities, similar to those of SN IMs. The metallicity distribution of SNe IIn can be reproduced by combining the metallicity distributions of SN IMs (which may be produced by major outbursts of massive stars like LBVs) and SNe IIP (produced by RSGs). The same applies to the distributions of the normalized cumulative rank (NCR) values, which quantifies the SN association to HII regions. For SNe IIn, we find larger mass-loss rates and higher CSM velocities at higher metallicities. The luminosity increment in the optical bands during SN IM outbursts tend to be larger at higher metallicity, whereas the SN IM quiescent optical luminosities tend to be lower. The difference in metallicity between SNe IIn and SN IMs indicates that LBVs are only one of the progenitor channels for SNe IIn, with 1988Z-like and 1998S-like SNe possibly arising from LBVs and RSGs, respectively. Finally, even though line-driven winds likely do not primarily drive the late mass-loss of CSI SN progenitors, metallicity has some impact on the observational properties of these transients.
- ID:
- ivo://CDS.VizieR/J/A+A/475/217
- Title:
- Classification of planetary nebulae
- Short Name:
- J/A+A/475/217
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we present a re-analysis of the criteria used to characterize the Peimbert classes I, IIa, IIb, III and IV, through a statistical study of a large sample of planetary nebulae previously classified according to these groups. In the original classification, it is usual to find planetary nebulae that cannot be associated with a single type; these most likely have dubious classifications into two or three types. Statistical methods can greatly contribute in providing a better characterization of planetary nebulae groups. We use the Bayes Theorem to calculate the posterior probabilities for an object to be member of each of the types I, IIa, IIb, III and IV. This calculation is particularly important for planetary nebulae that are ambiguously classified in the traditional method. The posterior probabilities are defined from the probability density function of classificatory parameters of a well-defined sample, composed only by planetary nebulae unambiguously fitted into the Peimbert types. Because the probabilities depend on the available observational data, they are conditional probabilities, and, as new observational data are added to the sample, the classification of the nebula can be improved, to take into account this new information. This method differs from the original classificatory scheme, because it provides a quantitative result of the representativity of the object within its group. Also, through the use of marginal distributions it is possible to extend the Peimbert classification even to those objects for which only a few classificatory parameters are known.
- ID:
- ivo://CDS.VizieR/J/AJ/125/197
- Title:
- CN abundances of the 47 Tuc main sequence
- Short Name:
- J/AJ/125/197
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a deep spectroscopic survey for star-to-star CN variations along the main sequence (MS) of the globular cluster 47 Tuc with ESO's Very Large Telescope. We find a significant bimodal distribution in the S(3839) index for main-sequence stars in the mass range ~0.85 to 0.65M_{sun}_, or from the main-sequence turnoff down to ~2.5 mag below the main-sequence turnoff. An anticorrelation of CN and CH is evident on the MS. The result is discussed in the context of the ability of faint MS stars to alter their surface composition through internal evolutionary effects. We argue against internal stellar evolution as the only origin for the abundance spread in 47 Tuc; an external origin such as pollution seems to be more likely.
- ID:
- ivo://CDS.VizieR/J/A+A/486/437
- Title:
- CN and CH line strengths in 8 Galactic GlCl
- Short Name:
- J/A+A/486/437
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our work focuses on the understanding of the origin of CNO-anomalies, which have been detected in several Galactic globular clusters. The novelty and advantage of this study is that it is based on a homogeneous data set of hundreds of medium-resolution spectra of stars in eight Galactic globular clusters (M 15, M 22, M 55, NGC 288, NGC 362, NGC 5286, Palomar 12, and Terzan 7). Two of the clusters (Palomar 12 and Terzan 7) are believed to be former members of the Sagittarius dwarf spheroidal (Sgr dSph) galaxy. The large homogeneous data set allows for a detailed differential study of the line strengths in the stellar spectra of the observed clusters. Our sample comprises stars in different evolutionary states, namely the main-sequence turn-off (MSTO) region, the subgiant branch (SGB) and the base of the red giant branch (RGB). We compare the relative CN and CH line strengths of stars in the same evolutionary states (with similar logg and T_eff_).
- ID:
- ivo://CDS.VizieR/J/A+A/319/235
- Title:
- CN in circumstellar envelopes survey
- Short Name:
- J/A+A/319/235
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We list in Table 1 the observed stars together with some of their characteristics. Distances, expansion velocities, mass loss rates, and spectral types are taken from the compilations of Bujarrabal et al. (1994) <J/A+A/285/247> and Loup et al. (1993A&AS...99..291). The sample includes C-rich and O-rich objects, some S-stars, a few proto-PN, and a young PN (NGC7027). See paper for more details. In Table 2, we give some of the observational parameters. A_low_ and A_high_ refer to the integrated intensity of the low-frequency and high-frequency fine-structure groups. The intrinsic intensity ratios, R=A_high_/A_low_, are R(1-0)=2 and R(2-1)=1.8. In principle, the observation of several components with different intrinsic strengths allows an estimate of the line optical depth, and the value of R gives an estimate of the envelope thickness.
- ID:
- ivo://CDS.VizieR/J/PASJ/57/65
- Title:
- CNO abundances of solar-type stars
- Short Name:
- J/PASJ/57/65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determined the C, N, and O abundances of 160 nearby F, G, and K dwarfs and subgiants by using spectra obtained with the HIDES spectrograph at Okayama Astrophysical Observatory, with the purposes of (1) establishing the runs of [C/Fe], [N/Fe], and [O/Fe] for these galactic disk stars in the metallicity range of -1<~[Fe/H]~<+0.4, (2) searching for any difference in the CNO abundances of planet-host stars as compared to non-planet-host stars, and (3) examining the consistency of the abundances derived from different lines to check the validity of the analysis. The non-LTE effect on the abundance determination was taken into consideration based on our extensive statistical-equilibrium calculations.
- ID:
- ivo://CDS.VizieR/J/ApJ/831/20
- Title:
- C/O and Mg/Si for solar neighborhood's stars
- Short Name:
- J/ApJ/831/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The carbon-to-oxygen ratio in a protoplanetary disk can have a dramatic influence on the compositions of any terrestrial planets formed. In regions of high C/O, planets form primarily from carbonates, and in regions of low C/O, the ratio of magnesium to silicon determines the types of silicates that dominate the compositions. We present C/O and Mg/Si ratios for 852 F, G, and K dwarfs in the solar neighborhood. We find that the frequency of carbon-rich dwarfs in the solar neighborhood is <0.13% and that 156 known planet hosts in the sample follow a similar distribution as all of the stars as a whole. The cosmic distribution of Mg/Si for these same stars is broader than the C/O distribution and peaks near 1.0, with ~60% of systems having 1<=Mg/Si<2, leading to rocky planet compositions similar to the Earth. This leaves 40% of systems that can have planets that are silicate-rich and that may have very different compositions than our own.
- ID:
- ivo://CDS.VizieR/J/A+A/489/1271
- Title:
- CO and OH abundances of 23 K-M giants
- Short Name:
- J/A+A/489/1271
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on the high resolution infrared spectra observed with the Fourier Transform Spectrometer (FTS) at the 4m telescope of the Kitt Peak National Observatory (KPNO), ro-vibrational lines of ^12^C^16^O, ^13^C^16^O, ^12^C^17^O, and ^16^OH were measured. Some details of the observed spectra including the resolution, S/N ratio, and data of observation are given in table2. The spectroscopic and equivalent width data are given in table3 for 23 red giant stars. The resulting data are used to investigate the nature of the infrared spectra of K-M giant stars. It is found that only the weak lines (log(W/nu)<-4.75) carry the information on the photosphere and hence can be used to extract the nature of the photosphere such as the stellar abundances. The intermediate-strength (-4.75<log(W/nu)<-4.40) as well as the strong (log(W/nu)>-4.4) lines are badly disturbed by the lines of non-photospheric origin. In other words, most lines dominating the infrared spectra, except for the weak lines, are actually hybrid of at least two different kinds of lines originating in the photosphere and in an extra molecular layers outside of photosphere. The nature of the extra layers is not known well, but it may be related to the molecular envelope producing H_2_O lines, not only in late M but also in early M giants as well. Also, the intermediate-strength lines include those with LEP as high as 2eV and hence the extra molecular layer should be quite warm. For the reason outlined above, we determine C, O, and their isotopic abundances using only the weak lines, but we listed the measured data not only of the weak lines but also of the stronger lines as well in table3, with the hope that these data can be of some use to clarify the nature of the warm extra molecular layers.
- ID:
- ivo://CDS.VizieR/J/ApJ/720/259
- Title:
- CO column densities in dark clouds
- Short Name:
- J/ApJ/720/259
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Data from the Five College Radio Astronomy Observatory CO Mapping Survey of the Taurus molecular cloud are combined with extinction data for a sample of 292 background field stars to investigate the uptake of CO from the gas to icy grain mantles on dust within the cloud. On the assumption that the reservoir of CO in the ices is represented well by the combined abundances of solid CO and solid CO_2_ (which forms by oxidation of CO on the dust), we find that the total column density (gas+solid) correlates tightly with visual extinction (A_V_) over the range 5mag<A_V_<30mag, i.e., up to the highest extinctions covered by our sample. The mean depletion of gas-phase CO, expressed as {delta}(CO)=N(CO)_ice_/N(CO)_total_, increases monotonically from negligible levels for A_V_<~5 to ~0.3 at A_V_=10 and ~0.6 at A_V_=30. As these results refer to line-of-sight averages, they must be considered lower limits to the actual depletion at loci deep within the cloud, which may approach unity. We show that it is plausible for such high levels of depletion to be reached in dense cores on timescales ~0.6Myr, comparable with their expected lifetimes. Dispersal of cores during star formation may be effective in maintaining observable levels of gaseous CO on the longer timescales estimated for the age of the cloud.
