arXiv subjects

E. Villaver

Publications and source records attributed to E. Villaver.

At least 73 records · Page 4Linked to original sources

arXiv2018

Fast spectrophotometry of WD 1145+017

WD 1145+017 is currently the only white dwarf known to exhibit periodic transits of planetary debris as well as absorption lines from circumstellar gas. We present the first simultaneous fast optical spectrophotometry and broad-band photometry of the system, obtained with the Gran Telescopio Canarias (GTC) and the Liverpool Telescope (LT), respectively. The observations spanned $5.5$ h, somewhat longer than the $4.5$-h orbital period of the debris. Dividing the GTC spectrophotometry into five wavelength bands reveals no significant colour differences, confirming grey transits in the optical. We argue that absorption by an optically thick structure is a plausible alternative explanation for the achromatic nature of the transits that can allow the presence of small-sized ($\simμ$m) particles. The longest ($87$ min) and deepest ($50$ per cent attenuation) transit recorded in our data exhibits a complex structure around minimum light that can be well modelled by multiple overlapping dust clouds. The strongest circumstellar absorption line, Fe II $λ$5169, significantly weakens during this transit, with its equivalent width reducing from a mean out-of-transit value of $2$ Å to $1$ Å in-transit, supporting spatial correlation between the circumstellar gas and dust. Finally, we made use of the Gaia Data Release 2 and archival photometry to determine the white dwarf parameters. Adopting a helium-dominated atmosphere containing traces of hydrogen and metals, and a reddening $E(B-V)=0.01$ we find $T_\mathrm{eff}=15\,020 \pm 520$ K, $\log g=8.07\pm0.07$, corresponding to $M_\mathrm{WD}=0.63\pm0.05\ \mbox{$\mathrm{M}_{\odot}$}$ and a cooling age of $224\pm30$ Myr.

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arXiv2018

Rotation of the asymptotic giant branch star R Doradus

High resolution observations of the extended atmospheres of asymptotic giant branch (AGB) stars can now directly confront the theories that describe stellar mass loss. Using Atacama Large Millimeter/submillimeter Array (ALMA) high angular resolution ($30\times42$~mas) observations we have, for the first time, resolved stellar rotation of an AGB star, R~Dor. We measure an angular rotation velocity of $ω_R\sin{i}=(3.5\pm0.3)\times10^{-9}$~rad~s$^{-1}$ which indicates a rotational velocity of $|\upsilon_{\rm rot}\sin{i}|=1.0\pm0.1$~km~s$^{-1}$ at the stellar surface ($R_*=31.2$~mas at $214$~GHz). The rotation axis projected on the plane of the sky has a position angle $Φ=7\pm6^\circ$. We find that the rotation of R Dor is two orders of magnitude faster than expected for a solitary AGB star that will have lost most of its angular momentum. Its rotational velocity is consistent with angular momentum transfer from a close companion. As a companion has not been directly detected we thus suggest R~Dor has a low-mass, close-in, companion. The rotational velocity approaches the critical velocity, set by the local sound speed in the extended envelope, and is thus expected to affect the mass loss characteristics of R~Dor.

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arXiv2018

The co-existence of hot and cold gas in debris discs

Debris discs have often been described as gas-poor discs as the gas-to-dust ratio is expected to be considerably lower than in primordial,protoplanetary discs. However, recent observations have confirmed the presence of a non-negligible amount of cold gas in the circumstellar (CS) debris discs around young main-sequence stars.This cold gas has been suggested to be related to the outgassing of planetesimals and cometary-like objects. The aim of the paper is to investigate the presence of hot gas in the surroundings of stars bearing cold-gas debris discs. High-resolution optical spectra of all currently known cold-gas-bearing debris-disc systems, with the exception of $β$ Pic and Fomalhaut, have been obtained from different observatories.We have analysed the Ca II H & K and the Na I D lines searching for non-photospheric absorptions of CS origin, usually attributed to cometary-like activity. Narrow, stable Ca II and/or Na I absorption features have been detected superimposed to the photospheric lines in 10 out of the 15 observed cold-gas-bearing debris disc.Features are found at the radial velocity of the stars, or slightly blue- or red-shifted, and/or at the velocity of the local interstellar medium (ISM). Some stars also present transient variable events or absorptions extended towards red wavelengths. These are the first detections of such Ca II features in 7 out of the 15 observed stars. In some of these stars, results suggest that the stable and variable absorptions arise from relatively hot gas located in the CS close-in environment. This hot gas is detected in at least ~80%, of edge-on cold-gas-bearing debris discs, while in only ~10% of the discs seen close to face-on. We interpret this as a geometrical effect, and suggest that the non-detection of hot gas absorptions is due to the disc inclination rather than to the absence of the hot-gas component.

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arXiv2018

Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. VI. HD 238914 and TYC 3318-01333-1 - two more Li-rich giants with planets

We present the latest results of our search for planets with HARPS-N at the 3.6 m Telescopio Nazionale Galileo under the Tracking Advanced Planetary Systems project: an in-depth study of the 15 most Li abundant giants from the PennState - Toruń Planet Search sample. Our goals are first, to obtain radial velocities of the most Li-rich giants we identified in our sample to search for possible low-mass substellar companions, and second, to perform an extended spectral analysis to define the evolutionary status of these stars. Methods. This work is based on high-resolution spectra obtained with the Hobby-Eberly Telescope and its High Resolution Spectro- graph, and with the HARPS-N spectrograph at the Telescopio Nazionale Galileo. Two stars, HD 181368 and HD 188214 , were also observed with UVES at the VLT to determine beryllium abundances. We report i) the discovery of two new planetary systems around the Li-rich giant stars: HD 238914 and TYC 3318-01333- 1 (a binary system); ii) reveal a binary Li-rich giant, HD 181368 ; iii) although our current phase coverage is not complete, we suggest the presence of planetary mass companions around TYC 3663-01966-1 and TYC 3105-00152-1 ; iv) we confirm the previous result for BD+48 740 and present updated orbital parameters, and v) we find a lack of a relation between the Li enhancement and the Be abundance for the stars HD 181368 and HD 188214 , for which we acquired blue spectra. We found seven stars with stellar or potential planetary companions among the 15 Li-rich giant stars. The binary star frequency of the Li-rich giants in our sample appears to be normal, but the planet frequency is twice that of the general sample, which suggests a possible connection between hosting a companion and enhanced Li abundance in giant stars. We also found most of the companions orbits to be highly eccentric.

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arXiv2018

GTC/CanariCam mid-IR imaging of the fullerene-rich Planetary Nebula IC 418: searching for the spatial distribution of fullerene-like molecules

We present seeing-limited narrow-band mid-IR GTC/CanariCam images of the spatially extended fullerene-containing planetary nebula (PN) IC 418. The narrow-band images cover the C60 fullerene band at 17.4 μm, the polycyclic aromatic hydrocarbon like (PAH-like) feature at 11.3 μm, the broad 9-13 μm feature, and their adjacent continua at 9.8 and 20.5 μm. We study the relative spatial distribution of these complex species, all detected in the Spitzer and Infrared Space Observatory (ISO) spectra of IC 418, with the aim of getting observational constraints to the formation process of fullerenes in H-rich circumstellar environments. A similar ring-like extended structure is seen in all narrow-band filters, except in the dust continuum emission at 9.8 μm, which peaks closer to the central star. The continuum-subtracted images display a clear ring-like extended structure for the carrier of the broad 9-13 μm emission, while the spatial distribution of the (PAH-like) 11.3 μm emission is not so well defined. Interestingly, a residual C60 17.4 μm emission (at about 4-σ from the sky background) is seen when subtracting the dust continuum emission at 20.5 μm. This residual C60 emission, if real, might have several interpretations; the most exciting being perhaps that other fullerene-based species like hydrogenated fullerenes with very low H-content may contribute to the observed 17.4 μm emission. We conclude that higher sensitivity mid-IR images and spatially resolved spectroscopic observations (especially in the Q-band) are necessary to get some clues about fullerene formation in PNe.

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arXiv2017

Chemical fingerprints of hot Jupiter planet formation

The current paradigm to explain the presence of Jupiters with small orbital periods (P $<$ 10 days; hot Jupiters) that involves their formation beyond the snow line following inward migration, has been challenged by recent works that explored the possibility of in situ formation. We aim to test whether stars harbouring hot Jupiters and stars with more distant gas-giant planets show any chemical peculiarity that could be related to different formation processes. Our results show that stars with hot Jupiters have higher metallicities than stars with cool distant gas-giant planets in the metallicity range +0.00/+0.20 dex. The data also shows a tendency of stars with cool Jupiters to show larger abundances of $α$ elements. No abundance differences between stars with cool and hot Jupiters are found when considering iron peak, volatile elements or the C/O, and Mg/Si ratios. The corresponding $p$-values from the statistical tests comparing the cumulative distributions of cool and hot planet hosts are 0.20, $<$ 0.01, 0.81, and 0.16 for metallicity, $α$, iron-peak, and volatile elements, respectively. We confirm previous works suggesting that more distant planets show higher planetary masses as well as larger eccentricities. We note differences in age and spectral type between the hot and cool planet hosts samples that might affect the abundance comparison. The differences in the distribution of planetary mass, period, eccentricity, and stellar host metallicity suggest a different formation mechanism for hot and cool Jupiters. The slightly larger $α$ abundances found in stars harbouring cool Jupiters might compensate their lower metallicities allowing the formation of gas-giant planets.

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arXiv2017

DZ Cha: a bona fide photoevaporating disc

DZ Cha is a weak-lined T Tauri star (WTTS) surrounded by a bright protoplanetary disc with evidence of inner disc clearing. Its narrow $\Ha$ line and infrared spectral energy distribution suggest that DZ Cha may be a photoevaporating disc. We aim to analyse the DZ Cha star + disc system to identify the mechanism driving the evolution of this object. We have analysed three epochs of high resolution optical spectroscopy, photometry from the UV up to the sub-mm regime, infrared spectroscopy, and J-band imaging polarimetry observations of DZ Cha. Combining our analysis with previous studies we find no signatures of accretion in the $\Ha$ line profile in nine epochs covering a time baseline of $\sim20$ years. The optical spectra are dominated by chromospheric emission lines, but they also show emission from the forbidden lines [SII] 4068 and [OI] 6300$\,Å$ that indicate a disc outflow. The polarized images reveal a dust depleted cavity of $\sim7$ au in radius and two spiral-like features, and we derive a disc dust mass limit of $M_\mathrm{dust}<3\MEarth$ from the sub-mm photometry. No stellar ($M_\star > 80 \MJup$) companions are detected down to $0\farcs07$ ($\sim 8$ au, projected). The negligible accretion rate, small cavity, and forbidden line emission strongly suggests that DZ Cha is currently at the initial stages of disc clearing by photoevaporation. At this point the inner disc has drained and the inner wall of the truncated outer disc is directly exposed to the stellar radiation. We argue that other mechanisms like planet formation or binarity cannot explain the observed properties of DZ Cha. The scarcity of objects like this one is in line with the dispersal timescale ($\lesssim 10^5$ yr) predicted by this theory. DZ Cha is therefore an ideal target to study the initial stages of photoevaporation.

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arXiv2017

The white dwarf binary pathways survey - II. Radial velocities of 1453 FGK stars with white dwarf companions from LAMOST DR4

We present the second paper of a series of publications aiming at obtaining a better understanding regarding the nature of type Ia supernovae (SNIa) progenitors by studying a large sample of detached F, G and K main sequence stars in close orbits with white dwarf companions (i.e. WD+FGK binaries). We employ the LAMOST (Large Sky Area Multi-Object Fibre Spectroscopic Telescope) data release 4 spectroscopic data base together with GALEX (Galaxy Evolution Explorer) ultraviolet fluxes to identify 1,549 WD+FGK binary candidates (1,057 of which are new), thus doubling the number of known sources. We measure the radial velocities of 1,453 of these binaries from the available LAMOST spectra and/or from spectra obtained by us at a wide variety of different telescopes around the globe. The analysis of the radial velocity data allows us to identify 24 systems displaying more than 3sigma radial velocity variation that we classify as close binaries. We also discuss the fraction of close binaries among WD+FGK systems, which we find to be ~10 per cent, and demonstrate that high-resolution spectroscopy is required to efficiently identify double-degenerate SNIa progenitor candidates.

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arXiv2017

Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. V.: A Massive Jupiter orbiting the very low metallicity giant star BD+03 2562 and a possible planet around HD~103485

We present two evolved stars from the TAPAS (Tracking Advanced PlAnetary Systems) with HARPS-N project devoted to RV precision measurements of identified candidates within the PennState - Torun Centre for Astronomy Planet Search. Evolved stars with planets are crucial to understand the dependency of the planet formation mechanism on the mass and metallicity of the parent star and to study star-planet interactions. The paper is based on precise radial velocity (RV) measurements, for HD 103485 we collected 57 epochs over 3317 days with the Hobby-Eberly Telescope and its High Resolution Spectrograph and 18 ultra-precise HARPS-N data over 919 days. For BD+03 2562 we collected 46 epochs of HET data over 3380 days and 19 epochs of HARPS-N data over 919 days. We present the analysis of the data and the search for correlations between the RV signal and stellar activity, stellar rotation and photometric variability. Based on the available data, we interpret the RV variations measured in both stars as Keplerian motion. Both stars have masses close to Solar (1.11 and 1.14), very low metallicities ([Fe/H]=-0.50 and -0.71), and, both have Jupiter planetary mass companions (m sin i=7 and 6.4 Mj), in close to terrestrial orbits (1.4 and 1.3~au), with moderate eccentricities (e=0.34 and 0.2). However, we cannot totally exclude that the signal in the case of HD~103485 is due to rotational modulation of active regions. Based on the current data, we conclude that BD+03 2562 has a bona fide planetary companion while for HD 103485 we cannot totally exclude that the best explanation for the RV signal modulations is not the existence of a planet but stellar activity. If, the interpretation remains that both stars have planetary companions they represent systems orbiting very evolved stars with very low metallicities, a challenge to the conditions required for the formation of massive giant gas planets.

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arXiv2017

Searching for chemical signatures of brown dwarf formation

Recent studies have shown that close-in brown dwarfs in the mass range 35-55 M$_{\rm Jup}$ are almost depleted as companions to stars, suggesting that objects with masses above and below this gap might have different formation mechanisms. We determine the fundamental stellar parameters, as well as individual abundances for a large sample of stars known to have a substellar companion in the brown dwarf regime. The sample is divided into stars hosting "massive" and "low-mass" brown dwarfs. Following previous works a threshold of 42.5 M$_{\rm Jup}$ was considered. Our results confirm that stars with brown dwarf companions do not follow the well-established gas-giant planet metallicity correlation seen in main-sequence planet hosts. Stars harbouring "massive" brown dwarfs show similar metallicity and abundance distribution as stars without known planets or with low-mass planets. We find a tendency of stars harbouring "less-massive" brown dwarfs of having slightly larger metallicity, [X$_{\rm Fe}$/Fe] values, and abundances of Sc II, Mn I, and Ni I in comparison with the stars having the massive brown dwarfs. The data suggest, as previously reported, that massive and low-mass brown dwarfs might present differences in period and eccentricity. We find evidence of a non-metallicity dependent mechanism for the formation of massive brown dwarfs. Our results agree with a scenario in which massive brown dwarfs are formed as stars. At high-metallicities, the core-accretion mechanism might become efficient in the formation of low-mass brown dwarfs while at lower metallicities low-mass brown dwarfs could form by gravitational instability in turbulent protostellar discs.

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arXiv2016

Constraining the mass of the planet(s) sculpting a disk cavity. The intriguing case of 2MASS J16042165-2130284

The large cavities observed in the dust and gas distributions of transition disks may be explained by planet-disk interactions. At ~145 pc, 2MASS J16042165-2130284 (J1604) is a 5-12 Myr old transitional disk with different gap sizes in the mm- and $μ$m-sized dust distributions (outer edges at ~79 and at ~63 au, respectively). Its $^{12}$CO emission shows a ~30 au cavity. This radial structure suggests that giant planets are sculpting this disk. We aim to constrain the masses and locations of plausible giant planets around J1604. We observed J1604 with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) at the Very Large Telescope (VLT), in IRDIFS\_EXT, pupil-stabilized mode, obtaining YJH- band images with the integral field spectrograph (IFS) and K1K2-band images with the Infra-Red Dual-beam Imager and Spectrograph (IRDIS). The dataset was processed exploiting the angular differential imaging (ADI) technique with high-contrast algorithms. Our observations reach a contrast of $ΔK, YH$ ~12 mag from 0.15" to 0.80" (~22 to 115 au), but no planet candidate is detected. The disk is directly imaged in scattered light at all bands from Y to K, and it shows a red color. This indicates that the dust particles in the disk surface are mainly $\gtrsim0.3\,μ$m-sized grains. We confirm the sharp dip/decrement in scattered light in agreement with polarized light observations. Comparing our images with a radiative transfer model we argue that the southern side of the disk is most likely the nearest. This work represents the deepest search yet for companions around J1604. We reach a mass sensitivity of $\gtrsim 2-3M_{Jup}$ from ~22 to ~115 au according to a hot start scenario. We propose that a brown dwarf orbiting inside of ~15 au and additional Jovian planets at larger radii could account for the observed properties of J1604 while explaining our lack of detection.

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arXiv2016

Exocomet signatures around the A-shell star $Φ$ Leo?

We present an intensive monitoring of high-resolution spectra of the Ca {\sc ii} K line in the A7IV shell star $Φ$ Leo at very short (minutes, hours), short (night to night), and medium (weeks, months) timescales. The spectra show remarkable variable absorptions on timescales of hours, days, and months. The characteristics of these sporadic events are very similar to most that are observed toward the debris disk host star $β$ Pic, which are commonly interpreted as signs of the evaporation of solid, comet-like bodies grazing or falling onto the star. Therefore, our results suggest the presence of solid bodies around $Φ$ Leo. To our knowledge, with the exception of $β$ Pic, our monitoring has the best time resolution at the mentioned timescales for a star with events attributed to exocomets. Assuming the cometary scenario and considering the timescales of our monitoring, our results indicate that $Φ$ Leo presents the richest environment with comet-like events known to date, second only to $β$ Pic.

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arXiv2016

Rotating Stars and the Formation of Bipolar Planetary Nebulae II: Tidal Spin-up

We present new binary stellar evolution models that include the effects of tidal forces, rotation, and magnetic torques with the goal of testing Planetary Nebulae (PNe) shaping via binary interaction. We explore whether tidal interaction with a companion can spin up the AGB envelope. To do so we have selected binary systems with main sequence masses of 2.5 \Mo and of 0.8 \Mo and evolve them allowing initial separations of 5, 6, 7, and 8 AU. The binary stellar evolution models have been computed all the way to the PNe formation phase or until Roche lobe overflow (RLOF) is reached, whatever happens first. We show that with initial separations of 7 and 8 AU, the binary avoids entering into RLOF, and the AGB star reaches moderate rotational velocities at the surface ($\sim 3.5 $ and $\sim 2 $ \kms respectively) during the inter-pulse phases, but after the thermal pulses it drops to a final rotational velocity of only $\sim 0.03 $ \kms. For the closest binary separations explored, 5 and 6 AU, the AGB star reaches rotational velocities of $\sim 6 $ and $\sim 4 $ \kms respectively when the RLOF is initiated. We conclude that the detached binary models that avoid entering the RLOF phase during the AGB will not shape bipolar PNe, since the acquired angular momentum is lost via the wind during the last two thermal pulses. This study rules out tidal spin-up in non-contact binaries as a sufficient condition to form bipolar PNe.

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arXiv2016

TAPAS IV. TYC 3667-1280-1 b - the most massive red giant star hosting a warm Jupiter

We present the latest result of the TAPAS project that is devoted to intense monitoring of planetary candidates that are identified within the PennState-Toruń planet search. We aim to detect planetary systems around evolved stars to be able to build sound statistics on the frequency and intrinsic nature of these systems, and to deliver in-depth studies of selected planetary systems with evidence of star-planet interaction processes. The paper is based on precise radial velocity measurements: 13 epochs collected over 1920 days with the Hobby-Eberly Telescope and its High-Resolution Spectrograph, and 22 epochs of ultra-precise HARPS-N data collected over 961 days. We present a warm-Jupiter ($T_{eq}=1350 K$, $m_{2} sin i=5.4\pm$0.4$M_{J}$) companion with an orbital period of 26.468 days in a circular ($e=0.036$) orbit around a giant evolved ($\log g=3.11\pm0.09$, $R=6.26\pm0.86R_{\odot}$) star with $M_{\star}=1.87\pm0.17M_{\odot}$. This is the most massive and oldest star found to be hosting a close-in giant planet. Its proximity to its host ($a=0.21au$) means that the planet has a $13.9\pm2.0\%$ probability of transits; this calls for photometric follow-up study. This massive warm Jupiter with a near circular orbit around an evolved massive star can help set constraints on general migration mechanisms for warm Jupiters and, given its high equilibrium temperature, can help test energy deposition models in hot Jupiters.

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arXiv2016

Evolved stars and the origin of abundance trends in planet hosts

Tentative evidence that the properties of evolved stars with planets may be different from what we know for MS hosts has been recently reported. We aim to test whether evolved stars with planets show any chemical peculiarity that could be related to the planet formation process. We determine in a consistent way the metallicity and individual abundances of a large sample of evolved (subgiants and red giants) and MS stars with and without known planetary companions. No differences in the <[X/Fe]> vs. condensation temperature (Tc) slopes are found between the samples of planet and non-planet hosts when all elements are considered. However, if the analysis is restricted to only refractory elements, differences in the Tc-slopes between stars with and without known planets are found. This result is found to be dependent on the stellar evolutionary stage, as it holds for MS and subgiant stars, while there seem to be no difference between planet and non-planet hosts among the sample of giants. A search for correlations between the Tc-slope and the stellar properties reveals significant correlations with the stellar mass and the stellar age. The data also suggest that differences in terms of mass and age between MS planet and non-planet hosts may be present. Our results are well explained by radial mixing in the Galaxy. The sample of giant contains stars more massive and younger than their MS counterparts. This leads to a sample of stars possibly less contaminated by stars not born in the solar neighbourhood, leading to no chemical differences between planet and non planet hosts. The sample of MS stars may contain more stars from the outer disc (specially the non-planet host sample) which might led to the differences observed in the chemical trends.

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arXiv2016

Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. III. HD 5583 and BD+15 2375 - two cool giants with warm companions

Evolved stars are crucial pieces to understand the dependency of the planet formation mechanism on the stellar mass and to explore deeper the mechanism involved in star-planet interactions. Over the past ten years, we have monitored about 1000 evolved stars for radial velocity variations in search for low-mass companions under the Penn State - Torun Centre for Astronomy Planet Search program with the Hobby-Eberly Telescope. Selected prospective candidates that required higher RV precision measurements have been followed with HARPS-N at the 3.6 m Telescopio Nazionale Galileo under the TAPAS project. We aim to detect planetary systems around evolved stars to be able to build sound statistics on the frequency and intrinsic nature of these systems, and to deliver in-depth studies of selected planetary systems with evidence of star-planet interaction processes. For HD 5583 we obtained 14 epochs of precise RV measurements collected over 2313 days with the Hobby-Eberly Telescope (HET), and 22 epochs of ultra-precise HARPS-N data collected over 976 days. For BD+15 2375 we collected 24 epochs of HET data over 3286 days and 25 epochs of HARPS-S data over 902 days. We report the discovery of two planetary mass objects orbiting two evolved Red Giant stars: HD~5583 has a m sin i = 5.78 M$_{J}$ companion at 0.529~AU in a nearly circular orbit (e=0.076), the closest companion to a giant star detected with the RV technique, and BD+15~2735 that with a m sin i= 1.06 M$_{J}$ holds the record of the lightest planet found so far orbiting an evolved star (in a circular e=0.001, 0.576~AU orbit). These are the third and fourth planets found within the TAPAS project, a HARPS-N monitoring of evolved planetary systems identified with the Hobby-Eberly Telescope.

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arXiv2015

TAPAS - Tracking Advanced Planetary Systems with HARPS-N. II. Super Li-rich giant HD 107028

Lithium rich giant stars are rare objects. For some of them, Li enrichment exceeds abundance of this element found in solar system meteorites, suggesting that these stars have gone through a Li enhancement process. We identified a Li rich giant HD 107028 with A(Li) > 3.3 in a sample of evolved stars observed within the PennState Torun Planet Search. In this work we study different enhancement scenarios and we try to identify the one responsible for Li enrichment for HD 107028. We collected high resolution spectra with three different instruments, covering different spectral ranges. We determine stellar parameters and abundances of selected elements with both equivalent width measurements and analysis, and spectral synthesis. We also collected multi epoch high precision radial velocities in an attempt to detect a companion. Collected data show that HD 107028 is a star at the base of Red Giant Branch. Except for high Li abundance, we have not identified any other anomalies in its chemical composition, and there is no indication of a low mass or stellar companion. We exclude Li production at the Luminosity Function Bump on RGB, as the effective temperature and luminosity suggest that the evolutionary state is much earlier than RGB Bump. We also cannot confirm the Li enhancement by contamination, as we do not observe any anomalies that are associated with this scenario. After evaluating various scenarios of Li enhancement we conclude that the Li-overabundance of HD 107028 originates from Main Sequence evolution, and may be caused by diffusion process.

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arXiv2015

Searching for signatures of planet formation in stars with circumstellar debris discs

(Abridged) Tentative correlations between the presence of dusty debris discs and low-mass planets have been presented. In parallel, detailed chemical abundance studies have reported different trends between samples of planet and non-planet hosts. We determine in a homogeneous way the metallicity, and abundances of a sample of 251 stars including stars with known debris discs, with debris discs and planets, and only with planets. Stars with debris discs and planets have the same [Fe/H] behaviour as stars hosting planets, and they also show a similar <[X/Fe]>-Tc trend. Different behaviour in the <[X/Fe]>-Tc trend is found between the samples of stars without planets and the samples of planet hosts. In particular, when considering only refractory elements, negative slopes are shown in cool giant planet hosts, whilst positive ones are shown in stars hosting low-mass planets. Stars hosting exclusively close-in giant planets show higher metallicities and positive <[X/Fe]>-Tc slope. A search for correlations between the <[X/Fe]>-Tc slopes and the stellar properties reveals a moderate but significant correlation with the stellar radius and as well as a weak correlation with the stellar age. The fact that stars with debris discs and stars with low-mass planets do not show neither metal enhancement nor a different <[X/Fe]>-Tc trend might indicate a correlation between the presence of debris discs and the presence of low-mass planets. We extend results from previous works which reported differences in the <[X/Fe]>-Tc trends between planet hosts and non hosts. However, these differences tend to be present only when the star hosts a cool distant planet and not in stars hosting exclusively low-mass planets.

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