arXiv subjects

A. Frasca

Publications and source records attributed to A. Frasca.

At least 73 records · Page 4Linked to original sources

arXiv2020

ISO-ChaI 52: a weakly-accreting young stellar object with a dipper light curve

We report on the discovery of periodic dips in the multiband lightcurve of ISO-ChaI 52, a young stellar object in the Chamaeleon I dark cloud. This is one among the peculiar objects that display very low or negligible accretion both in their UV continuum and spectral lines, although they present a remarkable infrared excess emission characteristic of optically-thick circumstellar disks. We have analyzed a VLT/X-Shooter spectrum with the tool ROTFIT to determine the stellar parameters. The latter, along with photometry from our campaign with the REM telescope and from the literature, have allowed us to model the spectral energy distribution and to estimate the size and temperature of the inner and outer disk. From the rotational period of the star/disk system of 3.45 days we estimate a disk inclination of 36$^\circ$. The depth of the dips in different bands has been used to gain information about the occulting material. A single extinction law is not able to fit the observed behavior, while a two-component model of a disk warp composed of a dense region with a gray extinction and an upper layer with an ISM-type extinction provides a better fit of the data.

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arXiv2020

X-Shooter survey of disk accretion in Upper Scorpius I. Very high accretion rates at age>5 Myr

Determining the mechanisms that drive the evolution of protoplanetary disks is a necessary step to understand how planets form. Here we measured the mass accretion rate for young stellar objects at age >5 Myr, a critical test for the current models of disk evolution. We present the analysis of the spectra of 36 targets in the ~5-10 Myr old Upper Scorpius region for which disk masses were measured with ALMA. We find that the mass accretion rates in this sample of old but still survived disks are similarly high as those of the younger (<3 Myr old) star-forming regions of Lupus and Cha I, when considering the dependence on stellar and disk mass. In particular, several disks show high mass accretion rates >10^-9 Msun/yr while having low disk masses. Furthermore, the median values of the measured mass accretion rates in the disk mass ranges where our sample is complete at a level ~60-80% are compatible in these three regions. At the same time, the spread of mass accretion rates at any given disk mass is still >0.9 dex even at age>5 Myr. These results are in contrast with simple models of viscous evolution, which would predict that the values of the mass accretion rate diminish with time, and a tighter correlation with disk mass at age>5 Myr. Similarly, simple models of internal photoevaporation cannot reproduce the observed mass accretion rates, while external photoevaporation might explain the low disk masses and high accretion rates. A partial possible solution to the discrepancy with the viscous models is that the gas-to-dust ratio of the disks at >5 Myr is significantly different and higher than the canonical 100, as suggested by some dust and gas disk evolution models. The results shown here require the presence of several inter-playing processes, such as detailed dust evolution, external photoevaporation and possibly MHD winds, to explain the secular evolution of protoplanetary disks.

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arXiv2020

The EXOTIME project: Signals in the $ O-C $ diagrams of the rapidly pulsating subdwarfs DW Lyn, V1636 Ori, QQ Vir, and V541 Hya

We aim to investigate variations in the arrival time of coherent stellar pulsations due to the light-travel time effect to test for the presence of sub-stellar companions. Those companions are the key to one possible formation scenario of apparently single sub-dwarf B stars. We made use of an extensive set of ground-based observations of the four large amplitude p-mode pulsators DW Lyn, V1636 Ori, QQ Vir, and V541 Hya. Observations of the TESS space telescope are available on two of the targets. The timing method compares the phase of sinusoidal fits to the full multi-epoch light curves with phases from the fit of a number of subsets of the original time series. Observations of the TESS mission do not sample the pulsations well enough to be useful due to the (currently) fixed two-minute cadence. From the ground-based observations, we infer evolutionary parameters from the arrival times. The residual signals show many statistically significant periodic signals, but no clear evidence for changes in arrival time induced by sub-stellar companions. The signals can be explained partly by mode beating effects. We derive upper limits on companion masses set by the observational campaign.

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arXiv2020

Discovery of new members of the nearby young stellar association in Cepheus

Young field stars are hardly distinguishable from older ones because their space motion rapidly mixes them with the stellar population of the Galactic plane. Nevertheless, a careful target selection allows for young stars to be spotted throughout the sky. We aim to identify additional sources associated with the four young comoving stars that we discovered towards the CO Cepheus void and to provide a comprehensive view of the Cepheus association. Based on multivariate analysis methods, we have built an extended sample of 193 young star candidates, which are the optical and infrared counterparts of ROSAT All-Sky Survey and XMM-Newton X-ray sources. From optical spectroscopic observations, we measured their radial velocity with the cross-correlation technique. We derived their atmospheric parameters and projected rotational velocity with the code ROTFIT. We applied the subtraction of inactive templates to measure the lithium equivalent width, from which we infer their lithium abundance and age. Finally, we studied their kinematics using the second Gaia data release. Our sample is mainly composed of young or active stars and multiple systems. We identify two distinct populations of young stars that are spatially and kinematically separated. Those with an age between 100 and 300 Myr are mostly projected towards the Galactic plane. In contrast, 23 of the 37 sources younger than 30 Myr are located in the CO Cepheus void, and 21 of them belong to the stellar kinematic group that we previously reported in this sky area. We report a total of 32 bona fide members and nine candidates for this nearby (distance = 157$\pm$10 pc) young (age = 10-20 Myr) stellar association. According to the spatial distribution of its members, the original cluster is already dispersed and partially mixed with the local population of the Galactic plane.

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arXiv2020

The disk of 2MASS 15491331-3539118 = GQ Lup C as seen by HST and WISE

Very recently, a second companion on wider orbit has been discovered around GQ Lup. This is a low-mass accreting star partially obscured by a disk seen at high inclination. If detected, this disk may be compared to the known disk around the primary. We detected this disk on archive HST and WISE data. The extended spectral energy distribution provided by these data confirms the presence of accretion from Halpha emission and UV excess, and shows an IR excess attributable to a warm disk. In addition, we resolved the disk on the HST images. This is found to be roughly aligned with the disk of the primary. Both of them are roughly aligned with the Lupus I dust filament containing GQ Lup.

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arXiv2020

The Gaia-ESO Survey: detection and characterization of single line spectroscopic binaries

Recent and on-going large ground-based multi-object spectroscopic surveys allow to significantly increase the sample of spectroscopic binaries to get insight into their statistical properties. We investigate the repeated spectral observations of the Gaia-ESO Survey (GES) internal data release 5 to identify and characterize spectroscopic binaries with one visible component (SB1) in fields covering the discs, the bulge, the CoRot fields, and stellar clusters and associations. A statistical chi2-test is performed on spectra of the iDR5 sub-sample of approximately 43500 stars characterized by at least 2 observations and a S/N > 3. Our sample of RV variables is cleaned from contamination by pulsation/convection-induced variables using Gaia DR2 parallaxes and photometry. Monte-Carlo simulations using the SB9 catalogue of spectroscopic orbits allow to estimate our detection efficiency and to correct the SB1 rate to evaluate the GES SB1 binary fraction and its dependence with effective temperature and metallicity. We find 641 (resp., 803) FGK SB1 candidates at the 5 sigma (resp., 3 sigma) level. The orbital-period distribution is estimated from the RV standard-deviation distribution and reveals that the detected SB1 probe binaries with log(P[d]) < 4. We estimate the global GES SB1 fraction to be in the range 7-14% with a typical uncertainty of 4%. The GES SB1 frequency decreases with metallicity at a rate of -9+/-3%/dex in the metallicity range -2.7<FeH<+0.6. This anticorrelation is obtained with a confidence level higher than 93% on a homogeneous sample covering spectral types FGK and a large range of metallicities. When the present-day mass function is accounted for, this rate turns to 4+/-2%/dex with a confidence level higher than 88%. In addition we provide the variation of the SB1 fraction with metallicity separately for F, G, and K spectral types, as well as for dwarf and giant primaries.

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arXiv2020

2MASS J15491331-3539118: a new low-mass wide companion of the GQ Lup system

Substellar companions at wide separation around stars hosting planets or brown dwarfs (BDs) yet close enough for their formation in the circumstellar disc are of special interest. In this letter we report the discovery of a wide (projected separation $\sim$16.0arcsec, or 2400 AU, and position angle 114.61$^\circ$) companion of the GQ Lup A-B system, most likely gravitationally bound to it. A VLT/X-Shooter spectrum shows that this star, 2MASS J15491331-3539118, is a bonafide low-mass ($\sim$0.15 M$_\odot$) young stellar object (YSO) with stellar and accretion/ejection properties typical of Lupus YSOs of similar mass, and with kinematics consistent with that of the GQ Lup A-B system. A possible scenario for the formation of the triple system is that GQ Lup A and 2MASS J15491331-3539118 formed by fragmentation of a turbulent core in the Lup I filament, while GQ Lup B, the BD companion of GQ Lup A at 0.7arcsec, formed in situ by the fragmentation of the circumprimary disc. The recent discoveries that stars form along cloud filaments would favour the scenario of turbulent fragmentation for the formation of GQ Lup A and 2MASS J15491331-3539118.

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arXiv2020

Multiwavelength behaviour of the blazar 3C279: decade-long study from $γ$-ray to radio

We report the results of decade-long (2008-2018) $γ$-ray to 1 GHz radio monitoring of the blazar 3C 279, including GASP/WEBT, $\it{Fermi}$ and $\it{Swift}$ data, as well as polarimetric and spectroscopic data. The X-ray and $γ$-ray light curves correlate well, with no delay > 3 hours, implying general co-spatiality of the emission regions. The $γ$-ray-optical flux-flux relation changes with activity state, ranging from a linear to a more complex dependence. The behaviour of the Stokes parameters at optical and radio wavelengths, including 43 GHz VLBA images, supports either a predominantly helical magnetic field or motion of the radiating plasma along a spiral path. Apparent speeds of emission knots range from 10 to 37c, with the highest values requiring bulk Lorentz factors close to those needed to explain $γ$-ray variability on very short time scales. The Mg II emission line flux in the `blue' and `red' wings correlates with the optical synchrotron continuum flux density, possibly providing a variable source of seed photons for inverse Compton scattering. In the radio bands we find progressive delays of the most prominent light curve maxima with decreasing frequency, as expected from the frequency dependence of the $τ=1$ surface of synchrotron self-absorption. The global maximum in the 86 GHz light curve becomes less prominent at lower frequencies, while a local maximum, appearing in 2014, strengthens toward decreasing frequencies, becoming pronounced at $\sim5$ GHz. These tendencies suggest different Doppler boosting of stratified radio-emitting zones in the jet.

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arXiv2019

Stellar population astrophysics (SPA) with the TNG. Characterization of the young open cluster ASCC 123

Star clusters are key to understand the stellar and Galactic evolution. ASCC 123 is a little-studied, nearby and very sparse open cluster. We performed the first high-resolution spectroscopic study of this cluster in the framework of the SPA (Stellar Population Astrophysics) project with GIARPS at the TNG. We observed 17 stars, five of which turned out to be double-lined binaries. Three of the investigated sources were rejected as members on the basis of astrometry and lithium content. For the remaining single stars we derived the stellar parameters, extinction, radial and projected rotational velocities, and chemical abundances for 21 species with atomic number up to 40. From the analysis of single main-sequence stars we found an average extinction $A_V\simeq 0.13$ mag and a median radial velocity of about $-5.6$ km/s. The average metallicity we found for ASCC 123 is [Fe/H]$\simeq+0.14\pm 0.04$, which is in line with that expected for its Galactocentric distance. The chemical composition is compatible with the Galactic trends in the solar neighborhood within the errors. From the lithium abundance and chromospheric H$α$ emission we found an age similar to that of the Pleiades, which agrees with that inferred from the Hertzsprung-Russell and color-magnitude diagrams.

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arXiv2019

GIARPS High-resolution Observations of T Tauri stars (GHOsT). I. Jet line emission

The mechanism for jet formation in the disks of T Tauri stars is poorly understood. Observational benchmarks to launching models can be provided by tracing the physical properties of the kinematic components of the wind and jet in the inner 100 au of the disk surface. In the framework of the GHOsT (GIARPS High-resolution Observations of T Tauri stars) project, we aim to perform a multi-line analysis of the velocity components of the gas in the jet acceleration zone. We analyzed the GIARPS-TNG spectra of six objects in the Taurus-Auriga complex (RY Tau, DG Tau, DL Tau, HN Tau, DO Tau, RW Aur A). Thanks to the combined high-spectral resolution (R=50000-115000) and wide spectral coverage (~400-2400 nm) we observed several O, S+, N, N+, and Fe+ forbidden lines spanning a large range of excitation and ionization conditions. In four objects (DG Tau, HN Tau, DO Tau, RW Aur A), temperature (T_e), electron and total density (n_e, n_H), and fractional ionization (x_e) were derived as a function of velocity through an excitation and ionization model. The abundance of gaseous iron, X(Fe), a probe of the dust content in the jet, was derived in selected velocity channels. The physical parameters vary smoothly with velocity, suggesting a common origin for the different kinematic components. In DG Tau and HN Tau, T_e, x_e, and X(Fe) increase with velocity (roughly from 6000 K, 0.05, 10% X(Fe)_sun to 15000 K, 0.6, 90% X(Fe)_sun). This trend is in agreement with disk-wind models in which the jet is launched from regions of the disk at different radii. In DO Tau and RW Aur A, we infer x_e < 0.1, n_H ~10^6-7 cm^-3, and X(Fe) <~ X(Fe)_sun at all velocities. These findings are tentatively explained by the formation of these jets from dense regions inside the inner, gaseous disk, or as a consequence of their high degree of collimation.

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arXiv2019

X-shooter spectroscopy of young stars with disks. The TW Hydrae association as a probe of the final stages of disk accretion

We investigate ongoing accretion activity in young stars in the TW Hydrae association (TWA, ~8-10 Myr), an ideal target to probe the final stages of disk accretion down to brown dwarf masses. Our sample comprises eleven TWA members with infrared excess, amounting to 85% of the total TWA population with disks, with spectral types between M0 and M9, and masses between 0.58 and 0.02 Msol. We employed homogeneous spectroscopic data from 300 to 2500 nm, obtained with X-shooter, to derive individual extinction, stellar parameters, and accretion parameters simultaneously. We then examined Balmer lines and forbidden emission lines to probe the physics of the star-disk interaction environment. We detected signatures of ongoing accretion for 70% of our TWA targets. This implies a fraction of accretors of 13-17% across the entire TWA (accounting for potentially accreting members not included in our survey). The spectral emission associated with these stars reveals a more evolved stage of these accretors compared to younger PMS populations: (i) a large fraction (~50%) exhibit nearly symmetric, narrow H_alpha line profiles; (ii) over 80% exhibit Balmer decrements consistent with moderate accretion and optically thin emission; (iii) less than a third exhibit forbidden line emission in [O I] 6300A, indicative of winds and outflows activity. However, the distribution in accretion rates (Mdot) derived for the TWA sample follows closely that of younger regions for Mstar~0.1-0.3 Msun. An overall correlation between Mdot and Mstar is detected, best reproduced by Mdot~Mstar^(2.1+/-0.5). At least in the lowest Mstar regimes, stars that still retain a disk at ages ~8-10 Myr are found to exhibit statistically similar, albeit moderate, accretion levels as those measured around younger objects. This slow Mdot evolution may be associated with longer evolutionary timescales of disks around low-mass stars.

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arXiv2019

The Gaia-ESO survey: Calibrating a relationship between Age and the [C/N] abundance ratio with open clusters

In the era of large high-resolution spectroscopic surveys, high-quality spectra can contribute to our understanding of the Galactic chemical evolution, providing chemical abundances belonging to the different nucleosynthesis channels, and also providing constraints to stellar age. Some abundance ratios have been proven to be excellent indicators of stellar ages. We aim at providing an empirical relationship between stellar ages and [C/N] using, as calibrators, open star clusters observed by both the Gaia-ESO and APOGEE surveys. We use stellar parameters and abundances from the Gaia-ESO and APOGEE of the Galactic field and open cluster stars. Ages of star clusters are retrieved from the literature sources and validated using a common set of isochrones. We use the same isochrones to determine, for each age and metallicity, the surface gravity at which the first dredge-up and red giant branch bump occur. We study the effect of extra-mixing processes in our sample of giant stars, and we derive the mean [C/N] in evolved stars, including only stars without evidence of extra-mixing. Combining the Gaia-ESO and APOGEE samples of open clusters, we derive a linear relationship between [C/N] and logarithmic cluster ages. We apply our relationship to selected giant field stars in both Gaia-ESO and APOGEE. We find an age separation between thin and thick disc stars and age trends within their populations, with an increasing age towards lower metallicity populations. With such empirical relationship, we are able to provide an age estimate for giant stars in which C and N abundances are measured. Isochrone fitting is less sensitive for giant than dwarf stars at the turn off. The present method can be thus considered as an additional tool to give an independent estimate of the age of giant stars, with uncertainties in their ages comparable to those obtained using isochrone fitting for dwarf stars.

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arXiv2019

The Gaia-ESO Survey: age spread in the star forming region NGC6530 from the HR diagram and gravity indicators

In very young clusters, stellar age distribution is the empirical proof of the duration of star formation (SF) and of the physical mechanisms involved in the process. We derived accurate stellar ages for the cluster NGC6530, associated with the Lagoon Nebula to infer its SF history. We use the Gaia-ESO survey observations and Gaia DR2 data, to derive cluster membership and fundamental stellar parameters. We identified 652 confirmed and 9 probable members. The reddening inferred for members and non-members allows us to distinguish MS stars and giants, in agreement with the distances inferred from Gaia DR2 data. The foreground and background stars show a spatial pattern that traces the 3D structure of the nebular dust component. We derive stellar ages for 382 confirmed cluster members and we find that the gravity-sensitive gamma index distribution for M stars is correlated with stellar age. For all members with Teff<5500 K, the mean logarithmic age is 5.84 (units of years) with a dispersion of 0.36 dex. The age distribution of stars with accretion and/or disk (CTTSe) is similar to that of stars without accretion and without disk (WTTSp). We interpret this dispersion as evidence of a real age spread since the total uncertainties on age determinations, derived from Monte Carlo simulations, are significantly smaller than the observed spread. This conclusion is supported by the evidence of a decreasing of the gravity-sensitive gamma index as a function of stellar ages. The presence of the age spread is also supported by the spatial distribution and the kinematics of old and young members. In particular, members with accretion and/or disk, formed in the last 1 Myr, show evidence of subclustering around the cluster center, in the Hourglass Nebula and in the M8-E region, suggesting a possible triggering of star formation events by the O-type star ionization fronts.

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arXiv2018

Contemporaneous broad-band photometry and H$α$ observations of T Tauri stars

The study of contemporaneous variations of the continuum flux and emission lines is of great importance to understand the different astrophysical processes at work in T Tauri stars. In this paper we present the results of a simultaneous $BVRI$ and H$α$ photometric monitoring, contemporaneous to medium-resolution spectroscopy of six T Tauri stars in the Taurus-Auriga star forming region. We have characterized the H$α$ photometric system using synthetic templates and the contemporaneous spectra of the targets. We show that we can achieve a precision corresponding to 2$-$3 Å in the H$α$ equivalent width, in typical observing conditions. The spectral analysis has allowed us to determine the basic stellar parameters and the values of quantities related to the accretion. In particular, we have measured a significant veiling only for the three targets with the strongest H$α$ emission (T Tau, FM Tau, and DG Tau). The broad-band photometric variations are found to be in the range 0.05$-$0.70 mag and are often paired to variations in the H$α$ intensity, which becomes stronger when the stellar continuum is weaker. In addition, we have mostly observed a redder $V-I$ and a bluer $B-V$ color as the stars become fainter. For most of the targets, the timescales of these variations seem to be longer than the rotation period. One exception is T Tau, for which the broad-band photometry varies with the rotation period. The most plausible interpretation of these photometric and H$α$ variations is that they are due to non-stationary mass accretion onto the stars, but rotational modulation can play a major role in some cases.

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arXiv2018

LAMOST observations in the Kepler field. II. Database of the low-resolution spectra from the five-year regular survey

The LAMOST-Kepler (LK-) project was initiated to use the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) to make spectroscopic follow-up observations for the targets in the field of the Kepler mission. The Kepler field is divided into 14 subfields that are adapted to the LAMOST circular field with a diameter of 5 degrees. During the regular survey phase of LAMOST, the LK-project took data from 2012 June to 2017 June and covered all the 14 subfields at least twice. In particular, we describe in this paper the second Data Release of the LK-project, including all spectra acquired through 2015 May to 2017 June together with the first round observations of the LK-project from 2012 June to 2014 September. The LK-project now counts 227 870 spectra of 156 390 stars, among which we have derived atmospheric parameters (log g, T eff and [Fe/H]) and heliocentric radial velocity (RV) for 173 971 spectra of 126 172 stars. These parameters were obtained with the most recent version of the LAMOST Stellar Parameter Pipeline v 2.9.7. Nearly one half, namely 76 283 targets, are observed both by LAMOST and Kepler telescopes. These spectra, establishing a large spectroscopy library, will be useful for the entire astronomical community, particularly for planetary science and stellar variability on Kepler targets.

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arXiv2018

Gaia DR2 view of the Lupus V-VI clouds: the candidate diskless young stellar objects are mainly background contaminants

Extensive surveys of star-forming regions with Spitzer have revealed populations of disk-bearing young stellar objects. These have provided crucial constraints, such as the timescale of dispersal of protoplanetary disks, obtained by carefully combining infrared data with spectroscopic or X-ray data. While observations in various regions agree with the general trend of decreasing disk fraction with age, the Lupus V and VI regions appeared to have been at odds, having an extremely low disk fraction. Here we show, using the recent Gaia data release 2 (DR2), that these extremely low disk fractions are actually due to a very high contamination by background giants. Out of the 83 candidate young stellar objects (YSOs) in these clouds observed by Gaia, only five have distances of 150 pc, similar to YSOs in the other Lupus clouds, and have similar proper motions to other members in this star-forming complex. Of these five targets, four have optically thick (Class II) disks. On the one hand, this result resolves the conundrum of the puzzling low disk fraction in these clouds, while, on the other hand, it further clarifies the need to confirm the Spitzer selected diskless population with other tracers, especially in regions at low galactic latitude like Lupus V and VI. The use of Gaia astrometry is now an independent and reliable way to further assess the membership of candidate YSOs in these, and potentially other, star-forming regions.

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arXiv2018

The Gaia-ESO Survey: the origin and evolution of s-process elements

Several works have found an increase of the abundances of the s-process neutron-capture elements in the youngest Galactic stellar populations, giving important constraints to stellar and Galactic evolution. We aim to trace the abundance patterns and the time-evolution of five s-process elements in the first peak, Y and Zr, and in the second peak, Ba, La and Ce using the Gaia-ESO idr5 results. From the UVES spectra of cluster member stars, we determined the average composition of clusters with ages >0.1 Gyr. We derived statistical ages and distances of field stars, and we separated them in thin and thick disc populations. We studied the time evolution and dependence on metallicity of abundance ratios using open clusters and field stars. Using our large and homogeneous sample of open clusters, thin and thick disc stars, spanning an age range larger than 10 Gyr, we confirm an increase towards young ages of s-process abundances in the Solar neighbourhood. These trends are well defined for open clusters and stars located nearby the solar position and they may be explained by a late enrichment due to significant contribution to the production of these elements from long-living low-mass stars. At the same time, we found a strong dependence of the s-process abundance ratios with the Galactocentric distance and with the metallicity of the clusters and field stars. Our results, derived from the largest and homogeneous sample of s-process abundances in the literature, confirm the growth with decreasing stellar ages of the s-process abundances in both field and open cluster stars. At the same time, taking advantage of the abundances of open clusters located in a wide Galactocentric range, they open a new view on the dependence of the s-process evolution on the metallicity and star formation history, pointing to different behaviours at various Galactocentric distances.

astro-ph.GA↗

arXiv2018

The Gaia-ESO Survey: properties of newly discovered Li-rich giants

We report 20 new lithium-rich giants discovered within the Gaia-ESO Survey, including the first Li-rich giant with evolutionary stage confirmed by CoRoT data. Atmospheric parameters and abundances were derived in model atmosphere analyses using medium-resolution GIRAFFE or high-resolution UVES spectra. These results are part of the fifth internal data release of Gaia-ESO. The Li abundances were corrected for non-LTE effects. We used Gaia DR2 parallaxes to estimate distances and luminosities. The giants have A(Li) > 2.2 dex. The majority of them (14 out of 20 stars) are in the CoRoT fields. Four giants are located in the field of three open clusters but are not members. Two giants were observed in fields towards the Galactic bulge but are likely in the inner disk. One of the bulge field giants is super Li-rich with A(Li) = 4.0 dex. We identified one giant with infrared excess at 22 microns. Two other giants, with large vsin i, might be Li-rich because of planet engulfment. Another giant is found to be barium enhanced and thus could have accreted material from a former AGB companion. Otherwise, besides the Li enrichment, the evolutionary stages are the only other connection between these new Li-rich giants. The CoRoT data confirm that one Li-rich giant is at the core-He burning stage. The other giants are concentrated in close proximity to the RGB luminosity bump, the core-He burning stages, or the early-AGB. This is very clear when looking at the Gaia-based luminosities of the Li-rich giants. This is also seen when the CoRoT Li-rich giants are compared to a larger sample of 2252 giants observed in the CoRoT fields by the Gaia-ESO Survey, which are distributed all over the RGB in the Teff-logg diagram. These observations show that evolutionary stage is a major factor behind the Li enrichment in giants. Other processes, like planet accretion, contribute to a smaller scale. [abridged]

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