ABSTRACT
In this paper, we present a detailed revision of the orbital parameters and the first quantitative abundance analysis of the spectroscopic triple system HD 226766. By means of a simultaneous ...fit of the radial velocities of all the three components, we derived precise orbital parameters for the system, in particular inner pair has P(d) = 31.9187 ± 0.0001, e = 0.28 ± 0.01, and MA/MB = 1.03 ± 0.03, while the C component orbits around the inner pair with a period of P(d) = 1615 ± 59 in a very eccentric orbit (e = 0.54 ± 0.11). From the fit of the Hβ and Hα profiles, we determined the effective temperatures and surface gravities of each component of the inner pair: Teff = 8600 ± 500 K and log g = 3.8 ± 0.2 for HD 226766 A and Teff = 8500 ± 400 K and log g = 4.0 ± 0.2 for HD 226766 B. In the hypothesis that component C is a main sequence star (log g = 4.0) we derived Teff = 8000 ± 500 K. Rotational velocities have been estimated by modeling the profiles of metallic lines: v sin i = 13 ± 1 km s−1 for inner pair and v sin i = 150 ± 20 km s−1 for the C component. We find that the inner pair is heterogeneous from the point of view of the chemical composition: both stars are very similar and show chemical anomalies typical of Am stars. With some hypothesis about the masses of the components, we estimated the orbital inclination angle for the inner binary, i = (47 ± 1)○, and for the outer orbit, i = (54 ± 19)○.
The Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST)-K2 (LK2) project, initiated in 2015, aims to collect low-resolution spectra of targets in the K2 campaigns, similar to the ...LAMOST-Kepler project. By the end of 2018, a total of 126 LK2 plates had been observed by LAMOST. After cross-matching the catalog of the LAMOST data release 6 (DR6) with that of the K2 approved targets, we found 160,619 usable spectra of 84,012 objects, most of which had been observed more than once. The effective temperature, surface gravity, metallicity, and radial velocity from 129,974 spectra for 70,895 objects are derived through the LAMOST Stellar Parameter Pipeline (LASP). The internal uncertainties were estimated to be 81 K, 0.15 dex, 0.09 dex, and 5 km s−1, respectively, when derived from a spectrum with a signal-to-noise ratio in the g band (S/Ng) of 10. These estimates are based on results for targets with multiple visits. The external accuracies were assessed by comparing the parameters of targets in common with the APOGEE and Gaia surveys, for which we generally found linear relationships. A final calibration is provided, combining external and internal uncertainties for giants and dwarfs, separately. We foresee that these spectroscopic data will be used widely in different research fields, especially in combination with K2 photometry.
ABSTRACT
In this paper, we present a spectroscopic study of six double-lined binaries, five of which were recently discovered in a high-resolution spectroscopic survey of optical counterparts of ...stellar X-ray sources. Thanks to high-resolution spectra acquired with CAOS spectropolarimeter during 7 yr, we were able to measure the radial velocities of their components and determine their orbital elements. We have applied our code compo2 to determine the spectral types and atmospheric parameters of the components of these spectroscopic binaries and found that two of these systems are composed of main-sequence stars, while the other four contain at least one evolved (giant or subgiant) component, similar to other well-known RS CVn systems. The subtraction of a photospheric template built up with spectra of non-active stars of the same spectral type as those of the components of each system has allowed us to investigate the chromospheric emission that fills in the H α cores. We found that the colder component is normally the one with the largest H α emission. None of the systems show a detectable Li iλ6708 line, with the exception of TYC 4279-1821-1, which exhibits high photospheric abundances in both components. Photometric time-series from the literature allowed us to assess that the five systems with a nearly circular orbit have also photometric periods close or equal to the orbital ones, indicating spin–orbit synchronization. For the system with a highly eccentric orbit, a possible pseudo-synchronization with the periastron velocity is suggested.
Aims. We present a detailed study of the two Sun-like stars KIC 7985370 and KIC 7765135, to determine their activity level, spot distribution, and differential rotation. Both stars were previously ...discovered by us to be young stars and were observed by the NASA Kepler mission. Methods. The fundamental stellar parameters (vsini, spectral type, Teff, log g, and Fe/H) were derived from optical spectroscopy by comparison with both standard-star and synthetic spectra. The spectra of the targets allowed us to study the chromospheric activity based on the emission in the core of hydrogen Hα and Ca ii infrared triplet (IRT) lines, which was revealed by the subtraction of inactive templates. The high-precision Kepler photometric data spanning over 229 days were then fitted with a robust spot model. Model selection and parameter estimation were performed in a Bayesian manner, using a Markov chain Monte Carlo method. Results. We find that both stars are Sun-like (of G1.5 V spectral type) and have an age of about 100–200 Myr, based on their lithium content and kinematics. Their youth is confirmed by their high level of chromospheric activity, which is comparable to that displayed by the early G-type stars in the Pleiades cluster. The Balmer decrement and flux ratio of their Ca ii-IRT lines suggest that the formation of the core of these lines occurs mainly in optically thick regions that are analogous to solar plages. The spot model applied to the Kepler photometry requires at least seven persistent spots in the case of KIC 7985370 and nine spots in the case of KIC 7765135 to provide a satisfactory fit to the data. The assumption of the longevity of the star spots, whose area is allowed to evolve with time, is at the heart of our spot-modelling approach. On both stars, the surface differential rotation is Sun-like, with the high-latitude spots rotating slower than the low-latitude ones. We found, for both stars, a rather high value of the equator-to-pole differential rotation (dΩ ≈ 0.18 rad d-1), which disagrees with the predictions of some mean-field models of differential rotation for rapidly rotating stars. Our results agree instead with previous works on solar-type stars and other models that predict a higher latitudinal shear, increasing with equatorial angular velocity, that can vary during the magnetic cycle.
We present the abundance analysis of a sample of more than 120 red giants in the globular cluster (GC) NGC 1851, based on FLAMES spectra. We find a small but detectable metallicity spread. This ...spread is compatible with the presence of two different groups of stars with a metallicity difference of 0.06-0.08 dex, in agreement with earlier photometric studies. If stars are divided into these two groups according to their metallicity, both components show Na-O anticorrelation (signature of a genuine GC nature) of moderate extension. The metal-poor stars are more concentrated than the metal-rich ones. We tentatively propose the hypothesis that NGC 1851 formed from a merger of two individual GCs with a slightly different Fe and {alpha}-element content and possibly an age difference up to 1 Gyr. This is also supported by number ratios of stars on the split subgiant and on the bimodal horizontal branches. The distribution of n-capture process elements in the two components also supports the idea that the enrichment must have occurred in each of the structures separately and not as a continuum of events in a single GC. The most probable explanation is that the proto-clusters formed into a (now dissolved) dwarf galaxy and later merged to produce the present GC.
Human mitochondrial cell-free DNA (Mt-cfDNA) may serve as a useful biomarker for infectious processes. We investigated Mt-cfDNA dynamics in patients with pulmonary mycobacterial infections to ...determine if this novel biomarker could be used to differentiate disease states and severity.
Patients with pulmonary tuberculosis (PTB), latent tuberculosis infection (LTBI), and nontuberculous mycobacterial-lung disease (NTM-LD) were enrolled at a tertiary care hospital in Taiwan between June 2018 and August 2021. Human Mt-cfDNA and nuclear-cfDNA (Nu-cfDNA) copy numbers were estimated by quantitative polymerase chain reaction. Variables associated with PTB and 2-month sputum culture-positivity, indicating poor treatment response, were assessed using logistic regression.
Among 97 patients with PTB, 64 with LTBI, and 51 with NTM-LD, Mt-cfDNA levels were higher in patients with PTB than in LTBI (p=0.001) or NTM-LD (p=0.006). In the
-infected population, Mt-cfDNA levels were highest in smear-positive PTB patients, followed by smear-negative PTB (p<0.001), and were lowest in LTBI persons (p=0.009). A Mt-cfDNA, but not Nu-cfDNA, level higher than the median helped differentiate culture-positive PTB from culture-negative PTB and LTBI (adjusted OR 2.430 95% CI 1.139-5.186, p=0.022) and differentiate PTB from NTM-LD (adjusted OR 4.007 1.382-12.031, p=0.011). Mt-cfDNA levels decreased after 2 months of treatment in PTB patients (p=0.010). A cutoff Mt-cfDNA level greater than 62.62 x 10
copies/μL-plasma was associated with a 10-fold risk of 2-month culture-positivity (adjusted OR 9.691 1.046-89.813, p=0.046).
Elevated Mt-cfDNA levels were associated with PTB disease and failed sputum conversion at 2 months in PTB patients, and decreased after treatment.
We present the abundance analysis of 82 red giant branch stars in the dense, metal-poor globular cluster NGC 6093 (M 80), the largest sample of stars analysed in this way for this cluster. From ...high-resolution UVES spectra of 14 stars and intermediate resolution GIRAFFE spectra for the other stars we derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu. On our UVES metallicity scale the mean metal abundance of M 80 is Fe/H = −1.791 ± 0.006 ± 0.076 (±statistical ±systematic error) with σ = 0.023 (14 stars). M 80 shows star-to-star variations in proton-capture elements, and the extension of the Na-O anti-correlation perfectly fit the relations with (i) total cluster mass; (ii) horizontal branch morphology; and (iii) cluster concentration previously found by our group. The chemistry of multiple stellar populations in M 80 does not look extreme. The cluster is also a representative of halo globular clusters concerning the pattern of α-capture and Fe-group elements. However we found that a significant contribution from the s-process is required to account for the distribution of neutron-capture elements. A minority of stars in M 80 seem to exhibit slightly enhanced abundances of s-process species, compatible with those observed in M 22 and NGC 1851, although further confirmation from larger samples is required.
HD 344787: a true Polaris analogue? Ripepi, V.; Catanzaro, G.; Molnár, L. ...
Astronomy and astrophysics (Berlin),
03/2021, Letnik:
647
Journal Article
Recenzirano
Odprti dostop
Context.
Classical Cepheids (DCEPs) are the most important primary indicators for the extragalactic distance scale, but they are also important objects in their own right, allowing us to place ...constraints on the physics of intermediate-mass stars and the pulsation theories.
Aims.
We have investigated the peculiar DCEP HD 344787, which is known to exhibit the fastest positive period change of DCEPs, along with a quenching amplitude of the light variation.
Methods.
We used high-resolution spectra obtained with HARPS-N at the TNG for HD 344787 and the more famous Polaris DCEP to infer their detailed chemical abundances. Results from the analysis of new time-series photometry of HD 344787 obtained by the TESS satellite are also reported.
Results.
The double-mode nature of the HD344787 pulsation is confirmed by an analysis of the TESS light curve, although with rather tiny amplitudes of a few dozen millimag. This is indication that HD344787 is on the verge of quenching the pulsation. Analysis of the spectra collected with HARPS-N at the TNG reveals an almost solar abundance and no depletion of carbon and oxygen. This means that the star appears to have not gone through first dredge-up. Similar results are obtained for Polaris.
Conclusions.
Polaris and HD344787 are both confirmed to be most likely at their first crossing of the instability strip. The two stars are likely at the opposite borders of the instability strip for first-overtone DCEPs with metal abundance
Z
= 0.008. A comparison with other DCEPs that are also thought to be at their first crossing allows us to speculate that the differences we see in the Hertzsprung-Russell diagram might be due to differences in the properties of the DCEP progenitors during the main-sequence phase.
ABSTRACT
The pulsating eclipsing binaries are remarkable systems that provide an opportunity to probe the stellar interior and to determine the fundamental stellar parameters precisely. Especially ...the detached eclipsing binary systems with (a) pulsating component(s) are significant objects to understand the nature of the oscillations since the binary effects in these systems are negligible. Recent studies based on space data have shown that the pulsation mechanisms of some oscillating stars are not completely understood. Hence, comprehensive studies of a number of pulsating stars within detached eclipsing binaries are important. In this study, we present a detailed analysis of the pulsating detached eclipsing binary system AI Hya which was studied by two independent groups with different methods. We carried out a spectroscopic survey to estimate the orbital parameters via radial velocity measurements and the atmospheric parameters of each binary component using the composite and/or disentangled spectra. We found that the more luminous component of the system is a massive, cool and chemically normal star while the hotter binary component is a slightly metal-rich object. The fundamental parameters of AI Hya were determined by the analysis of binary variations and subsequently used in the evolutionary modelling. Consequently, we obtained the age of the system as 850 ± 20 Myr and found that both binary components are situated in the δ Scuti instability strip. The frequency analysis revealed pulsation frequencies between 5.5 and 13.0 d−1 and we tried to estimate which binary component is the pulsating one. However, it turned out that those frequencies could originate from both binary components.
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