Examinando por Autor "Villaver, E."

Mostrando 1 - 5 de 5

Restringido
Do instabilities in high-multiplicity systems explain the existence of close-in white dwarf planets?
(Oxford Academics: Oxford University Press, 2021-02-03) Maldonado, R. F.; Villaver, E.; Mustill, A. J.; Chávez, M.; Bertone, E.; Consejo Nacional de Ciencia y Tecnología (CONACYT); National Aeronautics and Space Administration (NASA); Agencia Estatal de Investigación (AEI); Swedish Research Council
We investigate the origin of close-in planets and related phenomena orbiting white dwarfs (WDs), which are thought to originate from orbits more distant from the star. We use the planetary architectures of the 75 multiple-planet systems (four, five, and six planets) detected orbiting main-sequence stars to build 750 dynamically analogous templates that we evolve to the WD phase. Our exploration of parameter space, although not exhaustive, is guided and restricted by observations and we find that the higher the multiplicity of the planetary system, the more likely it is to have a dynamical instability (losing planets, orbit crossing, and scattering), that eventually will send a planet (or small object) through a close periastron passage. Indeed, the fraction of unstable four- to six-planet simulations is comparable to the 25–50 per cent fraction of WDs having atmospheric pollution. Additionally, the onset of instability in the four- to six-planet configurations peaks in the first Gyr of the WD cooling time, decreasing thereafter. Planetary multiplicity is a natural condition to explain the presence of close-in planets to WDs, without having to invoke the specific architectures of the system or their migration through the von Zeipel–Lidov–Kozai effects from binary companions or their survival through the common envelope phase.
Acceso Abierto
Exocomets: A spectroscopic survey
(EDP Sciences, 2020-07-01) Rebollido, I.; Eiroa, C.; Montesinos, B.; Maldonado, J.; Villaver, E.; Absil, O.; Bayo, A.; Canovas, H.; Carmona, A.; Chen, Ch.; Ertel, E.; Henning, T.; Iglesias, D. P.; Launhardt, R.; Liseau, R.; Meeus, G.; Moór, A.; Mora, A.; Olofsson, J.; Rauw, G.; Rivière Marichalar, P.; Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT); Ministerio de Economía y Competitividad (MINECO); 0000-0002-4388-6417; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. While exoplanets are now routinely detected, the detection of small bodies in extrasolar systems remains challenging. Since the discovery of sporadic events, which are interpreted to be exocomets (falling evaporating bodies) around β Pic in the early 1980s, only ∼20 stars have been reported to host exocomet-like events. Aims. We aim to expand the sample of known exocomet-host stars, as well as to monitor the hot-gas environment around stars with previously known exocometary activity. Methods. We have obtained high-resolution optical spectra of a heterogeneous sample of 117 main-sequence stars in the spectral type range from B8 to G8. The data were collected in 14 observing campaigns over the course of two years from both hemispheres. We analysed the Ca II K&H and Na I D lines in order to search for non-photospheric absorptions that originated in the circumstellar environment and for variable events that could be caused by the outgassing of exocomet-like bodies. Results. We detected non-photospheric absorptions towards 50% of the sample, thus attributing a circumstellar origin to half of the detections (i.e. 26% of the sample). Hot circumstellar gas was detected in the metallic lines inspected via narrow stable absorptions and/or variable blue- and red-shifted absorption events. Such variable events were found in 18 stars in the Ca II and/or Na I lines; six of them are reported in the context of this work for the first time. In some cases, the variations we report in the Ca II K line are similar to those observed in β Pic. While we do not find a significant trend in the age or location of the stars, we do find that the probability of finding CS gas in stars with larger v sin i is higher. We also find a weak trend with the presence of near-infrared excess and with anomalous (λ Boo-like) abundances, but this would require confirmation by expanding the sample.
Acceso Abierto
The A-shell star ϕ Leo revisited: its photospheric and circumstellar spectra
(EDP Sciences, 2021-09-21) Eiroa, C.; Montesinos, B.; Rebollido, I.; Henning, T.; Launhardt, R.; Maldonado, J.; Meeus, G.; Mora, A.; Rivière Marichalar, P.; Villaver, E.; Agencia Estatal de Investigación (AEI); Ministerio de Economía y Competitividad (MINECO); Istituto Nazionale di Astrofisica (INAF); Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. We previously suggested that variable red- and blueshifted absorption features observed in the Ca II K line towards the A-type shell star ϕ Leo are likely due to solid, comet-like bodies in the circumstellar (CS) environment. Aims. Our aim is to expand our observational study of ϕ Leo to other characteristic spectral lines of A-type photospheres as well as to lines arising in their CS shells. Methods. We obtained more than 500 high-resolution optical spectra collected at different telescopes over 37 nights in several observing runs from December 2015 to January 2019. Consecutive time-series spectra were taken, covering intervals of up to ~9 h on some nights. We analysed some photospheric lines, in particular Ca I 4226 Å and Mg II 4481 Å, as well as the circumstellar shell lines Ca II H and K, the Ca II IR triplet, Fe II 4924, 5018, and 5169 Å, Ti II 3685, 3759, and 3761 Å, and the Balmer lines Hα and Hβ. Results. Our observational study reveals that ϕ Leo is a variable δ Scuti star whose spectra show remarkable dumps and bumps superimposed on the photospheric line profiles, which vary in strength and sharpness, propagate from blue- to more redshifted radial velocities, and persist for a few hours. Similarly to other δ Scuti stars, these features are likely produced by non-radial pulsations. At the same time, all shell lines present emission at ~3 km s−1 centred at the core of the CS features, and two variable absorption minima at both sides of the emission; those absorption minima occur at almost the same velocity for each line, that is, no apparent dynamical evolution is observed. The variations observed in the Ca II H and K, Fe II, and Ti II lines occur on a range of timescales from minutes to days and between observing runs, but without any clear correlation or recognisable temporal pattern among the different lines. In the case of Hα, the CS contribution is also variable in just one of the observing runs. Conclusions. We suggest that ϕ Leo is a rapidly rotating δ Scuti star surrounded by a variable, (nearly) edge-on CS disk possibly re-supplied by the δ Scuti pulsations. The behaviour of the CS shell lines is reminiscent of that of rapidly rotating Be shell stars with an edge-on CS disk, and is clear evidence that the variations observed in the CS features of ϕ Leo are highly unlikely to be produced by exocomets. In addition, the observational results presented in this work, together with some recent results concerning the shell star HR 10, highlight the need for critical revision of the Ca II K features, which have been attributed to exocomets in other shell stars.
Acceso Abierto
Tracking Advanced Planetary Systems (TAPAS) with HARPS-N VII. Elder suns with low-mass companions
(EDP Sciences, 2021-04-13) Niedzielski, A.; Villaver, E.; Adamów, M.; Kowalik, K.; Wolszczan, A.; Maciejewski, G.; Polish National Science Centre; Agencia Estatal de Investigación (AEI); Maciejewski, G. [0000-0002-4195-5781]; Niedzielski, A. [https://orcid.org/0000-0002-0587-8854]
Context. We present the current status of and new results from our search for exoplanets in a sample of solar-mass evolved stars observed with the HARPS-N and the 3.6 m Telescopio Nazionale Galileo (TNG), and the High-Resolution Spectrograph (HRS) and the 9.2 m Hobby-Eberly Telescope (HET). Aims. The aim of this project is to detect and characterize planetary-mass companions to solar-mass stars in a sample of 122 targets at various stages of evolution from the main sequence to the red giant branch, mostly subgiants and giants, selected from the Pennsylvania-Toruń Planet Search sample, and to use this sample to study relations between stellar properties, such as metallicity, luminosity, and the planet occurrence rate. Methods. This work is based on precise radial velocity (RV) measurements. We have observed the program stars for up to 14 yr with the HET/HRS and the TNG/HARPS-N. Results. We present the analysis of RV measurements with the HET/HRS and the TNG/HARPS-N of four solar-mass stars, HD 4760, HD 96992, BD+02 3313, and TYC 0434-04538-1. We found that HD 4760 hosts a companion with a minimum mass of 13.9 MJ (a = 1.14 au, e = 0.23); HD 96992 is a host to a m sin i = 1.14 MJ companion on an a = 1.24 au and e = 0.41 orbit, and TYC 0434-04538-1 hosts an m sin i = 6.1 MJ companion on an a = 0.66 au and e = 0.08 orbit. In the case of BD+02 3313 we found a correlation between the measured RVs and one of the stellar activity indicators, suggesting that the observed RV variations may either originate in stellar activity or be caused by the presence of an unresolved companion. We also discuss the current status of the project and a statistical analysis of the RV variations in our sample of target stars. Conclusions. In our sample of 122 solar-mass stars, 49 ± 5% of them appear to be single and 16 ± 3% spectroscopic binaries. The three giants hosting low-mass companions presented in this paper join the six previously identified giants in the sample.
Restringido
Understanding the origin of white dwarf atmospheric pollution by dynamical simulations based on detected three-planet systems
(Oxford Academics: Oxford University Press, 2020-09-25) Maldonado, R. F.; Villaver, E.; Mustill, A. J.; Chavez, M.; Bertone, E.; Knut and Alice Wallenberg Foundation; Consejo Nacional de Ciencia y Tecnologia (CONACYT); Agencia Estatal de Investigación (AEI); Swedish Research Council (VR); Mustill, A. J. [0000-0002-2086-3642]; Bertone, E. [0000-0002-3751-0181]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Between 25 and 50 per cent of white dwarfs (WD) present atmospheric pollution by metals, mainly by rocky material, which has been detected as gas/dust discs, or in the form of photometric transits in some WDs. Planets might be responsible for scattering minor bodies that can reach stargazing orbits, where the tidal forces of the WD can disrupt them and enhance the chances of debris to fall on to the WD surface. The planet–planet scattering process can be triggered by the stellar mass-loss during the post main-sequence (MS) evolution of planetary systems. In this work, we continue the exploration of the dynamical instabilities that can lead to WD pollution. In a previous work, we explored two-planet systems found around MS stars and here we extend the study to three-planet system architectures. We evolved 135 detected three-planet systems orbiting MS stars to the WD phase by scaling their orbital architectures in a way that their dynamical properties are preserved using the N-body integrator package MERCURY. We find that 100 simulations (8.6 per cent⁠) are dynamically active (having planet losses, orbit crossing, and scattering) on the WD phase, where low-mass planets (1–100 M⊕) tend to have instabilities in Gyr time-scales, while high-mass planets (>100 M⊕) decrease the dynamical events more rapidly as the WD ages. Besides, 19 simulations (1.6 per cent⁠) were found to have planets crossing the Roche radius of the WD, where 9 of them had planet–star collisions. Our three-planet simulations have a slight increase in percentage of simulations that may contribute to the WD pollution than the previous study involving two-planet systems and have shown that planet–planet scattering is responsible of sending planets close to the WD, where they may collide directly to the WD, become tidally disrupted or circularize their orbits, hence producing pollution on the WD atmosphere.