arXiv subjects

M. Gómez

Publications and source records attributed to M. Gómez.

At least 37 records · Page 2Linked to original sources

arXiv2021

Physical characterization of recently discovered globular clusters in the Sagittarius dwarf spheroidal galaxy II. Metallicities, ages and luminosities

Globular clusters (GCs) are important tools to rebuild the accretion history of a galaxy. There are newly discovered GCs in the Sagittarius (Sgr) dwarf galaxy, that can be used as probes of the accretion event onto the Milky Way (MW). Our main aim is to characterize the Sgr GC system by measuring its main physical parameters. We build the optical and near-IR color-magnitude diagrams (CMDs) for 21 new Sgr GCs using the VISTA Variables in the Via Lactea Extended Survey (VVVX) near-IR database combined with the Gaia EDR3 optical database. We derive metallicities and ages for all targets, using the isochrone-fitting method and the RGB-slope and metallicity relation. The total luminosities are calculated both in the near-IR and in the optical. We construct the metallicity distribution (MD), the globular cluster luminosity function (GCLF), and the age-metallicity relation for the Sgr GC system. We find 17 metal-rich GCs with -0.9<[Fe/H]<-0.3, 4 metal-poor GCs with -2.0<[Fe/H]<-1.1 in the new Sgr GC sample. Even though our age estimates are rough, we find that the metal-poor GCs are consistent with an old population with an average age of ~13 Gyr, while the metal-rich GCs show a wider age range, between 6-8 Gyr and 10-13 Gyr. We compare the MD and the GCLF for the Sgr GC system with those of the MW, M31 and Large Magellanic Cloud (LMC) galaxies. We conclude that the majority of the metal-rich GCs are located within the main body of Sgr galaxy. We confirm that the GCLF is not a universal distribution, since the Sgr GCLF peaks at fainter luminosities than the GCLFs of the MW, M31 and LMC. The MD shows a double-peaked distribution, and we note that the metal-rich population looks like the MW bulge GCs. We compared our results with the literature concluding that the Sgr progenitor could have been a reasonably large galaxy able to retain the SNe ejecta, thus enriching its ISM.

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arXiv2021

An Intriguing Globular Cluster in the Galactic Bulge from the VVV Survey

Recent near-IR Surveys have discovered a number of new bulge globular cluster (GC) candidates that need to be further investigated. Our main objective is to use public data from the Gaia Mission, VVV, 2MASS and WISE in order to measure the physical parameters of Minni48, a new candidate GC located in the inner bulge of the Galaxy at l=359.35 deg, b=2.79 deg. Even though there is a bright foreground star contaminating the field, the cluster appears quite bright in near- and mid-IR images. We obtain deep decontaminated optical and near-IR colour-magnitude diagrams (CMDs) for this cluster. The heliocentric cluster distance is determined from the red clump (RC) and the red giant branch (RGB) tip magnitudes in the near-IR CMD, while the cluster metallicity is estimated from the RGB slope and the fit to theoretical isochrones. The GC size is found to be r = 6' +/- 1', while reddening and extinction values are E(J-Ks)=0.60 +/- 0.05 mag, A_G=3.23 +/- 0.10 mag, A_Ks=0.45 +/- 0.05 mag. The resulting mean Gaia proper motions are PMRA=-3.5 +/- 0.5 mas/yr, PMDEC=-6.0 +/- 0.5 mas/yr. The IR magnitude of the RC yields an accurate distance modulus estimate of (m-M)_0=14.61 mag, equivalent to a distance D=8.4 +/- 1.0 kpc. This is consistent with the optical distance estimate: (m-M)_0=14.67 mag, D=8.6 +/- 1.0 kpc, and with the RGB tip distance: (m-M)_0=14.45 mag, D=7.8 +/- 1.0 kpc. The derived metallicity is [Fe/H]=-0.20 +/- 0.30 dex. A good fit to the PARSEC stellar isochrones is obtained in all CMDs using Age = 10 +/- 2 Gyr. The total absolute magnitude of this GC is estimated to be M_Ks= -9.04 +/- 0.66 mag. Based on its position, kinematics, metallicity and age, we conclude that Minni48 is a genuine GC, similar to other well known metal-rich bulge GCs. It is located at a projected Galactocentric angular distance of 2.9 deg, equivalent to 0.4 kpc, being one of the closest GCs to the Galactic centre.

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arXiv2021

Eight more low luminosity globular clusters in the Sagittarius dwarf galaxy

Context. The Sagittarius (Sgr) dwarf galaxy is merging with the Milky Way, and the study of its globular clusters (GCs) is important to understand the history and outcome of this ongoing process. Aims. Our main goal is to characterize the GC system of the Sgr dwarf galaxy. This task is hampered by high foreground stellar contamination, mostly from the Galactic bulge. Methods. We performed a GC search specifically tailored to find new GC members within the main body of this dwarf galaxy using the combined data of the VISTA Variables in the Via Lactea Extended Survey (VVVX) near-infrared survey and the Gaia Early Data Release 3 (EDR3) optical database. Results. We applied proper motion (PM) cuts to discard foreground bulge and disk stars, and we found a number of GC candidates in the main body of the Sgr dwarf galaxy. We selected the best GCs as those objects that have significant overdensities above the stellar background of the Sgr galaxy and that possess color-magnitude diagrams (CMDs) with well-defined red giant branches (RGBs) consistent with the distance and reddening of this galaxy. Conclusions. We discover eight new GC members of the Sgr galaxy, which adds up to 29 total GCs known in this dwarf galaxy. This total number of GCs shows that the Sgr dwarf galaxy hosts a rather rich GC system. Most of the new GCs appear to be predominantly metal-rich and have low luminosity. In addition, we identify ten other GC candidates that are more uncertain and need more data for proper confirmation.

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arXiv2021

Discovery of new globular clusters in the Sagittarius dwarf galaxy

Context. Globular clusters (GCs) are witnesses of the past accretion events onto the Milky Way (MW). In particular, the GCs of the Sagittarius (Sgr) dwarf galaxy are important probes of an on-going merger. Aims. Our main goal is to search for new GC members of this dwarf galaxy using the VISTA Variables in the Via Lactea Extended Survey (VVVX) near-infrared database combined with the Gaia Early Data Release 3 (EDR3) optical database. Methods. We investigated all VVVX-enabled discoveries of GC candidates in a region covering about 180 sq. deg. toward the bulge and the Sgr dwarf galaxy. We used multiband point-spread function photometry to obtain deep color-magnitude diagrams (CMDs) and luminosity functions (LFs) for all GC candidates, complemented by accurate Gaia-EDR3 proper motions (PMs) to select Sgr members and variability information to select RR Lyrae which are potential GC members. Results. After applying a strict PM cut to discard foreground bulge and disk stars, the CMDs and LFs for some of the GC candidates exhibit well defined red giant branches and red clump giant star peaks. We selected the best Sgr GCs, estimating their distances, reddenings, and associated RR Lyrae. Conclusions. We discover 12 new Sgr GC members, more than doubling the number of GCs known in this dwarf galaxy. In addition, there are 11 other GC candidates identified that are uncertain, awaiting better data for confirmation.

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arXiv2021

Confirmation and physical characterization of the new bulge globular cluster Patchick 99 from the VVV and Gaia surveys

Globular clusters (GCs) are important tools to understand the formation and evolution of the Milky Way (MW). The known MW sample is still incomplete, so the discovery of new GC candidates and the confirmation of their nature are crucial for the census of the MW GC system. Our goal is to confirm the physical nature of two GC candidates: Patchick99 and TBJ3, located towards the Galactic bulge. We use public data in the near-IR from the VVV, VVVX and 2MASS along the with deep optical data from the Gaia DR2, in order to estimate their main physical parameters: reddening, extinction, distance, luminosity, mean cluster proper motions (PMs), size, metallicity and age. We investigate both candidates at different wavelengths. We use near-IR and optical CMDs in order to analyse Patchick99. We decontaminate CMDs following a statistical procedure and PM-selection. Reddening and extinction are derived by adopting reddening maps. Metallicity and age are evaluated by fitting stellar isochrones. Reddening and extinction are E(J-Ks)=0.12+/-0.02 mag, AKs=0.09+/-0.01 mag from the VVV data, whereas E(BP-RP)=0.21+/-0.03 mag, AG=0.68+/-0.08 mag from Gaia DR2. We estimate a distance d=6.4+/-0.2 kpc in near-IR and D=7.0+/-0.2 kpc in optical. We derive its metallicity and age fitting PARSEC isochrones, finding [Fe/H]=-0.2+/-0.2 dex and t=10+/-2 Gyr. The mean PMs for Patchick99 are pmRA=-298+/-1.74 mas/yr and pmDEC=-5.49+/-2.02 mas/yr. We confirm that it is a low-luminosity GC, with MKs=-7.0+/-0.6 mag. The radius estimation is performed building the radial density profile, finding r~10'. We recognise 7 RR Lyrae star members within 8.2 arcmin from its centre, confirming the distance found by other methods. We found that TBJ3 shows mid-IR emissions that are not present in GCs. We discard TBJ3 as GC candidate and we focus on Patchick99. We conclude that it is an old metal-rich GC, situated in the Galactic bulge.

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arXiv2020

ALMA detection of the dusty object silhouetted against the S0 galaxy NGC 3269 in the Antlia cluster

An intriguing silhouette of a small dust patch can be seen against the disk of the S0 galaxy NGC 3269 in the Antlia cluster in optical images. The images do not provide any clue as to whether the patch is a local Jupiter mass-scale cloudlet or a large extragalactic dust complex. We aim to resolve the nature of this object: is it a small Galactic cloudlet or an extragalactic dust complex? ALMA and APEX spectroscopy and Gemini GMOS long-slit spectroscopy were used to measure the velocity of the patch and the NGC 3269 disk radial velocity curve. A weak 16$\pm$2.5 km/s wide $^{12}$CO (2-1) T$_{MB}$ 19$\pm$2.5 mK line in a 2.0" by 2.12" beam associated with the object was detected with ALMA. The observed heliocentric velocity, V$_r$,hel = 3878$\pm$5.0km/s, immediately establishes the extragalactic nature of the object. The patch velocity is consistent with the velocity of the nucleus of NGC 3269, but not with the radial velocity of the NGC 3269 disk of the galaxy at its position. The $\sim$4" angular size of the patch corresponds to a linear size of $\sim$1 kpc at the galaxy's Hubble distance of (d/50.7 Mpc)$^2$ Msun, while the attenuation derived from the optical spectrum implies a dust mass of $\sim$2.6x10$^4$ (d/50.7 Mpc)$^2$ Msun. The derived attenuation ratio A'$_B$/(A'$_B$-A'$_R$) of 1.6$\pm$0.11 is substantially lower than the corresponding value for the mean Milky Way extinction curve for point sources (2.3). We established the extragalactic nature of the patch, but its origin remains elusive. One possibility is that the dust patch is left over from the removal of interstellar matter in NGC 3269 through the interaction with its neighbour, NGC 3268.

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arXiv2020

VVVX-Gaia Discovery of a Low Luminosity Globular Cluster in the Milky Way Disk

Milky Way globular clusters (MW GCs) are difficult to identify at low Galactic latitudes because of high differential extinction and heavy star crowding. The new deep near-IR images and photometry from the VISTA Variables in the Via Láctea Extended Survey (VVVX) allow us to chart previously unexplored regions. Our long term aim is to complete the census of MW GCs. The immediate goals are to estimate the astrophysical parameters, measuring their reddenings, extinctions, distances, total luminosities, proper motions, sizes, metallicities and ages. We use the near-IR VVVX survey database, in combination with Gaia DR2 optical photometry, and with the Two Micron All Sky Survey (2MASS) photometry. We report the detection of a heretofore unknown Galactic Globular Cluster at $RA =$ 14:09:00.0; $DEC=-$65:37:12 (J2000). We calculate a reddening of $E(J-K_s)=(0.3\pm 0.03)$ mag and an extinction of $A_{K_s}=(0.15\pm 0.01)$ mag for this new GC. Its distance modulus and corresponding distance were measured as $(m-M)=(15.93\pm0.03)$ mag and $D=(15.5\pm1.0)$ kpc, respectively. We estimate the metallicity and age by comparison with known GCs and by fitting PARSEC and Dartmouth isochrones, finding $[Fe/H]=(-0.70\pm0.2)$ dex and $t=(11.0\pm1.0)$ Gyr. The mean GC PMs from Gaia are $μ_{α^\ast}=(-4.68 \pm 0.47 )$ mas $yr^{-1}$ and $μ_δ=(-1.34 \pm 0.45)$ mas $yr^{-1}$. The total luminosity of our cluster is estimated to be $M_{Ks}=(-7.76\pm 0.5)$ mag. We have found a new low-luminosity, old and metal-rich globular cluster, situated in the far side of the Galactic disk, at $R_{G}=11.2$ kpc from the Galactic centre, and at $z=1.0$ kpc below the plane. Interestingly, the location, metallicity and age of this globular cluster are coincident with the Monoceros Ring (MRi) structure.

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arXiv2019

Gemini-GRACES high-quality spectra of Kepler evolved stars with transiting planets I. Detailed characterization of multi-planet systems Kepler-278 and Kepler-391

(abridged) Kepler-278 and Kepler-391 are two of the three evolved stars known to date on the RGB to host multiple short-period transiting planets. Moreover, these planets are among the smallest discovered around RGB stars. Here we present a detailed stellar and planetary characterization of these remarkable systems. Based on high-quality spectra from Gemini-GRACES for Kepler-278 and Kepler-391, we obtained refined stellar parameters and precise chemical abundances for 25 elements. Also, combining our new stellar parameters with a photodynamical analysis of the Kepler light curves, we determined accurate planetary properties of both systems. The precise spectroscopic parameters of Kepler-278 and Kepler-391, along with their high $^{12}\mathrm{C}/^{13}\mathrm{C}$ ratios, show that both stars are just starting their ascent on the RGB. The planets Kepler-278b, Kepler-278c, and Kepler-391c are warm sub-Neptunes, whilst Kepler-391b is a hot sub-Neptune that falls in the hot super-Earth desert and, therefore, it might be undergoing photoevaporation of its outer envelope. The high-precision obtained in the transit times allowed us not only to confirm Kepler-278c's TTV signal, but also to find evidence of a previously undetected TTV signal for the inner planet Kepler-278b. From the presence of gravitational interaction between these bodies we constrain, for the first time, the mass of Kepler-278b ($M_{\mathrm{p}}$ = 56 $\substack{+37\\-13}$ $M_{\mathrm{\oplus}}$) and Kepler-278c ($M_{\mathrm{p}}$ = 35 $\substack{+9.9\\ -21} $ $M_{\mathrm{\oplus}}$). Finally, our photodynamical analysis also shows that the orbits of both planets around Kepler-278 are highly eccentric ($e \sim$ 0.7) and, surprisingly, coplanar. Further observations of this system are needed to confirm the eccentricity values presented here.

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arXiv2019

Discarding orbital decay in WASP-19b after one decade of transit observations

We present a empirical study of orbital decay for the exoplanet WASP-19b, based on mid-time measurements of 74 complete transits (12 newly obtained by our team and 62 from the literature), covering a 10-year baseline. A linear ephemeris best represents the mid-transit times as a function of epoch. Thus, we detect no evidence of the shortening of WASP-19b's orbital period and establish an upper limit of its steady changing rate, $\dot{P}=-2.294$ ms $yr^{-1}$, and a lower limit for the modified tidal quality factor $Q'_{\star} = (1.23 \pm 0.231) \times 10^{6}$. Both are in agreement with previous works. This is the first estimation of $Q'_{\star}$ directly derived from the mid-times of WASP-19b obtained through homogeneously analyzed transit measurements. Additionally, we do not detect periodic variations in the transit timings within the measured uncertainties in the mid-times of transit. We are therefore able to discard the existence of planetary companions in the system down to a few $M_\mathrm{\oplus}$ in the first order mean-motion resonances 1:2 and 2:1 with WASP-19b, in the most conservative case of circular orbits. Finally, we measure the empirical $Q'_{\star}$ values of 15 exoplanet host stars which suggest that stars with $T_\mathrm{eff}$ $\lesssim$ 5600K dissipate tidal energy more efficiently than hotter stars. This tentative trend needs to be confirmed with a larger sample of empirically measured $Q'_{\star}$.

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arXiv2018

The curious case of the companion: evidence for cold accretion onto a dwarf satellite near the isolated elliptical NGC 7796

The isolated elliptical (IE) NGC 7796 is accompanied by an interesting early-type dwarf galaxy, named NGC7796-DW1. It exhibits a tidal tail, very boxy isophotes, and multiple nuclei or regions (A, B, and C) that are bluer than the bulk population of the galaxy, indicating a younger age. These properties are suggestive of a dwarf-dwarf merger remnant. We use the Multi-Unit Spectroscopic Explorer (MUSE) at the VLT to investigate NGC 7796-DW1. We extract characteristic spectra to which we apply the STARLIGHT population synthesis software to obtain ages and metallicities of the various population components of the galaxy. The galaxy's main body is old and metal-poor. A surprising result is the extended line emission in the galaxy, forming a ring-like structure with a projected diameter of 2.2 kpc. The line ratios fall into the regime of HII-regions, although OB-stellar populations cannot be identified by spectral signatures. Nucleus A is a relatively old (7 Gyr or older) and metal-poor super star cluster, most probably the nucleus of the dwarf, now displaced. The star-forming regions B and C show younger and distinctly more metal-rich components. The emission line ratios of regions B and C indicate an almost solar oxygen abundance, if compared with radiation models of HII regions. NGC7796-DW1 occupies a particular role in the group of transition-type galaxies with respect to its origin and current evolutionary state, being the companion of an IE. The dwarf-dwarf merger scenario is excluded because of the missing metal-rich merger component. A viable alternative is gas accretion from a reservoir of cold, metal-rich gas. NGC7796 has to provide this gas within its X-ray bright halo. As illustrated by NGC7796-DW1, cold accretion may be a general solution to the problem of extended star formation histories in transition dwarf galaxies. (abridged)

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arXiv2017

Testing the Planet-Metallicity Correlation in M-dwarfs with Gemini GNIRS Spectra

While the planet-metallicity correlation for FGK main-sequence stars hosting giant planets is well established, the results are not so clear for M-dwarf stars, for which precise metallicity measurements are not straightforward. However, new techniques using near infrared spectra show promising results. Using these, we determine stellar parameters and metallicities for a sample of 16 M-dwarf stars, 11 of which host planets, with near-infrared spectra from the Gemini Near-Infrared Spectrograph (GNIRS). We find that M-dwarfs with planets are preferentially metal-rich compared to those without planets. This result, based on GNIRS spectra, is supported by the analysis of a relatively larger sample of M stars with planets (18 in total) and a control sample of 213 M stars without known planets, obtained from the catalogue of Terrien et al. (2015). This, on the one hand, coincides with the trend (not only for M- but also for solar-type stars) reported in the literature and, on the other hand, demonstrates the utility of GNIRS spectra to obtain reliable stellar parameters of M stars. We also find that M dwarfs that harbor giant planets are preferentially more metallic than those associated with low-mass planets (Neptune or super-Earth type). This trend also agrees with that previously reported for solar-type stars. These results would favor the core accretion model for planetary formation.

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arXiv2017

A search for transit timing variations and orbital decay in WASP-46b

We present 12 new transit observations of the exoplanet WASP-46b obtained with the 1.54-m telescope at Estación Astrofísica de Bosque Alegre (EABA, Argentina) and the 0.40-m Horacio Ghielmetti and 2.15-m Jorge Sahade telescopes at Complejo Astronómico El Leoncito (CASLEO, Argentina). We analyse them together with 37 light curves from the literature to re-determine the physical parameters and search for additional planets via transit timing variations (TTVs). We consider the 31 transits with uncertainties in their mid-transit times ($e_\mathrm{T_{0}}$) $<$ 1 minute, to perform the first homogeneous study of TTVs for the system, finding a dispersion of $σ= 1.66$ minutes over a 6 year baseline. Since no periodic variations are found, our interpretation for this relatively high value of $σ$ is that the stellar activity could be affecting the measured mid-transit times. This value of dispersion allows us to rule out the presence of additional bodies with masses larger than 2.3, 4.6, 7, and 9.3 $M_{\mathrm{\bigoplus}}$ at the first-order mean-motion resonances 2:1, 3:2, 4:3, and 5:4 with the transiting planet, respectively. Despite the 6 year baseline and a typical light curve precision of $2 \times 10^{-3}$, we find that we cannot significantly demonstrate a slow decrease of the orbital period of WASP-46b. We place a lower limit of Q$_{\star}$ > $7 \times 10^{3}$ on the tidal quality factor and determine that an additional 6 year baseline is required to rule out Q$_{\star}$ < $10^{5}$.

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arXiv2017

The globular cluster system of NGC 1316 IV. Nature of the star cluster complex SH2

The light of the merger remnant NGC 1316 is dominated by old and intermediate-age stars. The only sign of current star formation in this big galaxy is the HII region SH2, an isolated star cluster complex with a ring-like morphology and an estimated age of 0.1 Gyr at a galactocentric distance of about 35 kpc. A nearby intermediate-age globular cluster, surrounded by weak line emission and a few more young star clusters, is kinematically associated. The origin of this complex is enigmatic. The nebular emission lines permit a metallicity determination which can discriminate between a dwarf galaxy or other possible precursors. We used the Integrated Field Unit of the VIMOS instrument at the Very Large Telescope of the European Southern Observatory to study the morphology, kinematics, and metallicity employing line maps, velocity maps, and line diagnostics of a few characteristic spectra. The line ratios of different spectra vary, indicating highly structured HII regions, but define a locus of uniform metallicity. The strong-line diagnostic diagrams and empirical calibrations point to a nearly solar or even super-solar oxygen abundance. The velocity dispersion of the gas is highest in the region offset from the bright clusters. Star formation may be active on a low level. There is evidence for a large-scale disk-like structure in the region of SH2, which would make the similar radial velocity of the nearby globular cluster easier to understand. The high metallicity does not fit to a dwarf galaxy as progenitor. We favour the scenario of a free-floating gaseous complex having its origin in the merger 2 Gyr ago. Over a long period the densities increased secularly until finally the threshold for star formation was reached. SH2 illustrates how massive star clusters can form outside starbursts and without a considerable field population.

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arXiv2016

Molecular gas in the star-forming region IRAS 08589-4714

We present an analysis of the region IRAS 08589-4714 with the aim of characterizing the molecular environment. We observed the CO(3-2), ^{13}CO(3-2), C^{18}O(3-2), HCO+(3-2), and HCN(3-2) molecular lines in a region of 150" x 150", centered on the IRAS source, to analyze the distribution and characteristics of the molecular gas linked to the IRAS source. The molecular gas distribution reveals a molecular clump that is coincident with IRAS 08589-4714 and with a dust clump detected at 1.2 mm. The molecular clump is 0.45 pc in radius and its mass and H_2 volume density are 310 Mo and 1.2 x 10^4 cm^{-3}, respectively. Two overdensities were identified within the clump in HCN and HCO lines. A comparison of the LTE and virial masses suggests that the clump is collapsing in regions that harbor young stellar objects. An analysis of the molecular lines suggests that they are driving molecular outflows.

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arXiv2016

The IRAS 08589-4714 star-forming region

We present an analysis of the IRAS 08589-4714 star-forming region. This region harbors candidate young stellar objects identified in the WISE and Herschel images using color index criteria and spectral energy distributions (SEDs). The SEDs of some of the infrared sources and the 70 microns radial intensity profile of the brightest source (IRS 1) are modeled from Herschel fluxes using the one-dimensional radiative transfer DUSTY code. For these objects, we estimate the envelope masses, sizes, densities, and luminosities which suggest that they are very young, massive and luminous objects at early stages of the formation process. Color-color diagrams in the bands of WISE and 2MASS are used to identify potential young objects in the region. Those identified in the bands of WISE would be contaminated by the emission of PAHs. We use the emission distribution in the infrared at 70 and 160 microns, to estimate the dust temperature gradient. This suggests that the nearby massive star-forming region RCW 38, located ~ 10 pc of the IRAS source position may be contributing to the photodissociation of the molecular gas and to the heating of the interstellar dust in the environs of the IRAS source.

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arXiv2015

KIC 9821622: An interesting lithium-rich giant in the Kepler field

We report the discovery of a new exceptional young lithium-rich giant, KIC 9821622, in the \textit{Kepler} field that exhibits an unusually large enhancement of $α$, Fe-peak, and \textit{r}-process elements. From high-resolution spectra obtained with GRACES at Gemini North, we derived fundamental parameters and detailed chemical abundances of 23 elements from equivalent widths and synthesis analysis. By combining atmospheric stellar parameters with available asteroseismic data, we obtained the stellar mass, radius, and age. The data analysis reveals that KIC 9821622 is a Li-rich (A(Li)$_{NLTE}$ = 1.80 $\pm$ 0.2) intermediate-mass giant star ($M$ = 1.64 $M_{\odot}$) located at the red giant branch near the luminosity bump. We find unexpectedly elevated abundances of Fe-peak and \textit{r}-process elements. In addition, as previously reported, we find that this is a young star (2.37 Gyr) with unusually high abundances of $α$-elements ([$α$/Fe] = 0.31). The evolutionary status of KIC 9821622 suggests that its Li-rich nature is the result of internal fresh Li that is synthesized through the Cameron-Fowler mechanism near the luminosity bump. However, its peculiar enhancement of $α$, Fe-peak, and \textit{r}-process elements opens the possibility of external contamination by material enriched by a supernova explosion. Although it is less likely, planet accretion cannot be ruled out.

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arXiv2014

Stellar parameters and chemical abundances of 223 evolved stars with and without planets

We present fundamental stellar parameters and chemical abundances for a sample of 86 evolved stars with planets and for a control sample of 137 stars without planets. The analysis was based on both high S/N and resolution echelle spectra. The goals of this work are i) to investigate chemical differences between stars with and without planets; ii) to explore potential differences between the properties of the planets around giants and subgiants; and iii) to search for possible correlations between these properties and the chemical abundances of their host stars. In agreement with previous studies, we find that subgiants with planets are, on average, more metal-rich than subgiants without planets by ~ 0.16 dex. The [Fe/H] distribution of giants with planets is centered at slightly subsolar metallicities and there is no metallicity enhancement relative to the [Fe/H] distribution of giants without planets. Furthermore, contrary to recent results, we do not find any clear difference between the metallicity distributions of stars with and without planets for giants with M > 1.5 Msun. With regard to the other chemical elements, the analysis of the [X/Fe] distributions shows differences between giants with and without planets for some elements, particularly V, Co, and Ba. Analyzing the planet properties, some interesting trends might be emerging: i) multi-planet systems around evolved stars show a slight metallicity enhancement compared with single-planet systems; ii) planets with a $\lesssim$ 0.5 AU orbit subgiants with [Fe/H] > 0 and giants hosting planets with a $\lesssim$ 1 AU have [Fe/H] < 0; iii) higher-mass planets tend to orbit more metal-poor giants with M < 1.5 Msun, whereas planets around subgiants seem to follow the planet-mass metallicity trend observed on dwarf hosts; iv) planets orbiting giants show lower orbital eccentricities than those orbiting subgiants and dwarfs.

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arXiv2013

No Transit Timing Variations in WASP-4

We present 6 new transits of the system WASP-4. Together with 28 light curves published in the literature, we perform an homogeneous study of its parameters and search for variations in the transit's central times. The final values agree with those previously reported, except for a slightly lower inclination. We find no significant long-term variations in $i$ or $R_{P}/R_{\star}$. The $O-C$ mid-transit times do not show signs of TTVs greater than 54 s.

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