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- ID:
- ivo://CDS.VizieR/J/A+A/626/A95
- Title:
- HD160305 images with SPHERE
- Short Name:
- J/A+A/626/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Direct imaging of debris disks gives important information about their nature, their global morphology and allows to identify specific structures possibly in connection with the presence of gravitational perturbers. It is the most straightforward technique to observe planetary systems as a whole. We present the first resolved images of the debris disk around the young F-type star HD 160305, detected in scattered light using the VLT/SPHERE instrument in the near infrared. We used a post-processing method based on Angular Differential Imaging and synthetic images of debris disks produced with a disk modeling code (GRaTer) to constrain the main characteristics of the disk around HD160305. All of the point sources in the field of the IRDIS camera were analyzed with an astrometric tool to determine whether they are bound objects or background stars. We detect a very inclined (~82{deg}) ring-like debris disk located at a stellocentric distance of about 86au (deprojected width ~27au). The disk displays a brightness asymmetry between the two sides of the major axis, as can be expected from scattering properties of dust grains. We derive an anisotropic scattering factor g>0.5. A second right-left asymmetry is also observed with respect to the minor axis. We measure a surface brightness ratio of 0.73+/-0.18 between the bright and the faint sides. Because of the low signal-to-noise ratio (S/N) of the images we cannot easily discriminate between several possible explanations for this left-right asymmetry, such as perturbations by an unseen planet, the aftermath of the breakup of a massive planetesimal, or the pericenter glow effect due to an eccentric ring. Two epochs of observations allow us to reject the companionship hypothesis for the 15 point sources present in the field.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A6
- Title:
- HD 219134 light and RV curves and code
- Short Name:
- J/A+A/635/A6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By analysing the transit light-curve of a planet-hosting star or the induced radial velocity oscillations, many useful information on the planet may be retrieved. However, inferring the physical parameters of the planet (mass, size, semi-major axis, etc.) requires the preliminary knowledge of some parameters of the host star, especially its mass and/or radius, that are generally inferred through theoretical evolutionary models. The paper aims at presenting and testing a whole algorithm devoted to the complete characterization of an exoplanetary system thanks to the global analysis of photometric and/or radial velocity time-series combined to observational stellar parameters derived either from spectroscopy or photometry. We developed an integrated tool called MCMCI that combines the Markov Chain Monte Carlo (MCMC) approach for analysing photometric and/or radial velocity time-series with a proper interpolation within stellar evolutionary isochrones and tracks (known as Isochrone placement) to be performed at each chain step, to retrieve stellar theoretical parameters, such as age, mass and radius. We tested the MCMCI both on the HD 219134 multiplanetary system hosting two transiting rocky super-Earths and on WASP-4, that hosts a bloated hot Jupiter. Even considering different input approaches, a final convergence was reached within the code, we found good agreement with the results already stated in the literature and we obtained more precise output parameters, especially concerning planetary masses. The MCMCI tool offers the opportunity of performing an integrated analysis of an exoplanetary system, without splitting it into the preliminary stellar characterization through theoretical models, but rather favouring a close interaction between the light-curve analysis and the isochrones, so that the parameters recovered at each step of the MCMC enter as input of the Isochrone placement.
- ID:
- ivo://CDS.VizieR/J/AJ/159/9
- Title:
- HD 150382 lithium-rich star at the early-AGB stage
- Short Name:
- J/AJ/159/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of a lithium-rich giant, HD 150382, a post-red-giant-branch clump star. The atmospheric parameters, the chemical abundances for 17 elements, and the isotopic ratio ^12^C/^13^C were determined using the equivalent width and the spectral synthesis methods. The lithium abundance was determined via spectral synthesis of the Li I resonance doublet at {lambda} 6708 yielding log{epsilon}(Li)_NLTE_=2.55. The excited-state line at {lambda} 6104 also was analyzed. In addition, we have used theoretical evolutionary tracks to determine the mass and luminosity of HD 150382 and compare it with other well-known lithium-rich giants in the literature. Our results show that HD 150382 is a slowly rotating K-giant star having near-solar metallicity. We also show that HD 150382 is not s-process enriched, which is in agreement with its evolutionary status. Finally, based on the abundance results, we study the possible scenarios of the lithium enrichment.
- ID:
- ivo://CDS.VizieR/J/A+A/647/A97
- Title:
- HD 183656 Long-term variations
- Short Name:
- J/A+A/647/A97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the latest results of a long-term observational project aimed at observing, collecting from the literature, and homogenising the light, colour, and spectral variations of the well-known emission-line Be star V923 Aql. Our analysis of these parameters confirms that all of the observables exhibit cyclic changes with variable cycle length between about 1800 and 3000 days, so far documented for seven consecutive cycles. We show that these variations can be qualitatively understood within the framework of the model of one-armed oscillation of the circumstellar disk, with a wave of increased density and prograde revolution in space. We confirm the binary nature of the object with a 214.716 day period and estimate the probable system properties. We also confirm the presence of rapid light, and likely also spectral changes. However, we cannot provide any firm conclusions regarding their nature. A quantitative modelling study of long-term changes is planned as a follow-up to this work.
8036. HD193571 NaCo images
- ID:
- ivo://CDS.VizieR/J/A+A/627/A77
- Title:
- HD193571 NaCo images
- Short Name:
- J/A+A/627/A77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interaction between low-mass companions and the debris disks they reside in is still not fully understood. A debris disk can evolve due to self-stirring, a process in which planetesimals can excite their neighbours to the point of destructive collisions. On top of this, the presence of a companion could further stir the disk (companion-stirring). Additional information is necessary to understand this fundamental step in the formation and evolution of a planetary system, and at the moment of writing only a handful of systems are known in which both a companion and a debris disk have been detected and studied at the same time. Our primary goal is to augment the sample of such systems and understand the relative importance between self-stirring and companion-stirring. In the course of the VLT/NaCo-ISPY Imaging Survey for Planets around Young stars, we observed HD 193571, an A0 debris disk hosting star at a distance of 68 pc with an age between 60-170Myr. We obtained two sets of observations in L' band and a third epoch in H band using the GPI instrument at Gemini-South. A companion was detected in all three epochs at a projected separation of 11au (0.17-arcsec), and co-motion was confirmed through proper motion analysis. Given the inferred disk size of 120au, the companion appears to reside within the gap between the host star and the disk. Comparison between the L' and H band magnitude and evolutionary tracks suggests a mass of 0.31-0.39M_{sun}_. We discovered a previously unknown M-dwarf companion around HD 193571, making it the third low-mass stellar object discovered within a debris disk. Comparison to self- and companion-stirring models suggests that the companion is likely responsible for the stirring of the disk.
- ID:
- ivo://CDS.VizieR/J/A+A/506/85
- Title:
- HD 50844 observed by CoRoT
- Short Name:
- J/A+A/506/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work presents the results obtained on HD 50844, the only delta Sct star observed in the CoRoT Initial Run (57.6d). The aim of these CoRoT observations was to investigate and characterize for the first time the pulsational behaviour of a delta Sct star, when observed at a level of precision and with a much better duty cycle than from the ground. The 140016 datapoints were analysed using independent approaches (SigSpec software and different iterative sine-wave fittings) and several checks performed (splitting of the timeseries in different subsets, investigation of the residual light curves and spectra. A level of 10^-5^mag was reached in the amplitude spectra of the CoRoT timeseries. The space monitoring was complemented by ground-based high-resolution spectroscopy, which allowed the mode identification of 30 terms. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0-30d^-1^. All the cross-checks confirmed this new result. The initial guess that delta Sct stars have a very rich frequency content is confirmed. The spectroscopic mode identification gives theoretical support since very high-degree modes (up to ell=14) are identified. We also prove that cancellation effects are not sufficient in removing the flux variations associated to these modes at the noise level of the CoRoT measurements. The ground-based observations indicate that HD 50844 is an evolved star that is slightly underabundant in heavy elements, located on the Terminal Age Main Sequence. Probably due to this unfavourable evolutionary status, no clear regular distribution is observed in the frequency set. The predominant term f1=6.92d^-1^ has been identified as the fundamental radial mode combining ground-based photometric and spectroscopic data. The CoRoT scientific programme contains other delta Sct stars, with different evolutionary statuses. The very rich and dense frequency spectrum discovered in the light curve of HD 50844 is the starting point for future investigations.
- ID:
- ivo://CDS.VizieR/J/A+A/503/945
- Title:
- HD 145788, 21 Peg and pi Cet chemical analysis
- Short Name:
- J/A+A/503/945
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Modern spectroscopy of early-type stars often aims at studying complex physical phenomena such as stellar pulsation, the peculiarity of the composition of the photosphere, chemical stratification, the presence of a magnetic field, and its interplay with the stellar atmosphere and the circumstellar environment. Comparatively less attention is paid to identifying and studying the "normal" A- and B-type stars and testing how the basic atomic parameters and standard spectral analysis allow one to fit the observations. By contrast, this kind of study is paramount for eventually allowing one to correctly quantify the impact of the various physical processes that occur inside the atmospheres of A- and B-type stars. We wish to establish whether the chemical composition of the solar photosphere can be regarded as a reference for early A- and late B-type stars.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A25
- Title:
- HD27130 photometric light curves
- Short Name:
- J/A+A/645/A25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The derivation of accurate and precise masses and radii is possible for eclipsing binary stars, allowing for insights into their evolution. When residing in star clusters, they provide measurements of even greater precision, along with additional information on their properties. Asteroseismic investigations of solar-like oscillations offers similar possibilities for single stars. We wish to improve the previously established properties of the Hyades eclipsing binary HD 27130 and re-assess the asteroseismic properties of the giant star {epsilon} Tau. The physical properties of these members of the Hyades can be used to constrain the helium content and age of the cluster. New multi-colour light curves were combined with multi-epoch radial velocities to yield masses and radii of HD 27130. Measurements of Teff were derived from spectroscopy and photometry, and verified using the Gaia parallax. We estimated the cluster age from re-evaluated asteroseismic properties of {epsilon} Tau while using HD 27130 to constrain the helium content. The masses, radii, and Teff of HD 27130 were found to be M=1.0245+/-0.0024M_{sun}_, R=0.9226+/-0.015R_{sun}_, Teff=5650+/-50K for the primary, and M=0.7426+/-0.0016M_{sun}_, R=0.7388+/-0.026R_{sun}_, Teff=4300+/-100K for the secondary component. Our re-evaluation of {epsilon} Tau suggests that the previous literature estimates are trustworthy and that the HIPPARCOS parallax is more reliable than the Gaia DR2 parallax. The helium content of HD 27130 and, thus, of the Hyades is found to be Y=0.27 but with a significant model dependency. Correlations with the adopted metallicity result in a robust helium enrichment law, with {DELTA}Y/{DELTA}Z close to 1.2 We estimate the age of the Hyades to be 0.9+/-0.1(stat)+/-0.1(sys)Gyr, which is in slight tension with recent age estimates based on the cluster white dwarfs. The precision of the age estimate can be much improved via asteroseismic investigations of the other Hyades giants and by future improvements to the Gaia parallax for bright stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/818/120
- Title:
- H_2_ d^3^{Pi}_u_ excitation by electron impact
- Short Name:
- J/ApJ/818/120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Electron-impact excitation of H_2_ triplet states plays an important role in the heating of outer planet upper thermospheres. The d^3^{Pi}_u_ state is the third ungerade triplet state, and the d^3^{Pi}_u_-a^3^{Sigma}_g_^+^ emission is the largest cascade channel for the a^3^{Sigma}_g_^+^ state. Accurate energies of the d^3^{Pi}_u_^-^(v, J) levels are calculated from an ab initio potential energy curve. Radiative lifetimes of the d^3^{Pi}_u_(v,J) levels are obtained by an accurate evaluation of the d^3^{Pi}_u_-a^3^{Sigma}_g_^+^ transition probabilities. The emission yields are determined from experimental lifetimes and calculated radiative lifetimes and are further verified by comparing experimental and synthetic d^3^{Pi}_u_-a^3^{Sigma}_g_^+^ spectra at 20eV impact energy. Spectral analysis revealed that multipolar components beyond the dipolar term are required to model the X^1^{Sigma}_g_^+^-d^3^{Pi}_u_ excitation, and significant cascade excitation occurs at the d^3^{Pi}_u_ (v=0,1) levels. Kinetic energy (E_k_) distributions of H atoms produced via predissociation of the ^3^{Pi}_u_ state and the d^3^{Pi}_u_-a^3^{Sigma}_g_^+^-b^3^{Sigma}_u_^+^ cascade dissociative emission are obtained. Predissociation of the d^3^{Pi}_u_ state produces H atoms with an average E_k_ of 2.3+/-0.4 eV/atom, while the E_k_distribution of the d^3^{Pi}_u_-a^3^{Sigma}_g_^+^-b^3^{Sigma}_u_^+^ channel is similar to that of the X^1^{Sigma}_g_^+^-a^3^{Sigma}_g_^+^-b^3^{Sigma}_u_^+^ channel and produces H(1s) atoms with an average E_k_ of 1.15+/-0.05eV/atom. On average, each H_2_ excited to the d^3^{Pi}_u_ state in an H_2_-dominated atmosphere deposits 3.3+/-0.4eV into the atmosphere, while each H_2_directly excited to the a^3^{Sigma}_g_^+^ state gives 2.2-2.3eV to the atmosphere. The spectral distribution of the calculated a^3^{Sigma}_g_^+^-b^3^{Sigma}_u_^+^ continuum emission due to the X^1^{Sigma}_g_^+^-d^3^{Pi}_u_ excitation is significantly different from that of direct a^3^{Sigma}_g_^+^ excitation.