arXiv subjects

R. Alonso

Publications and source records attributed to R. Alonso.

At least 127 records · Page 7Linked to original sources

arXiv2016

WD 1145+017 Photometric Observations During 8 Months of High Activity

WD 1145+017 was observed from 2015 November to 2016 July for the purpose of characterizing transit behavior of the white dwarf by dust clouds thought to be produced by fragments of an asteroid in close orbit with the star. Fortuitously, most of these observations were carried out during a time when the overall `dip' activity was dramatically enhanced over that during its discovery with Kepler K2. By the end of our reported observations the dip activity had declined to a level close to its K2 discovery state. Three notable events were observed. In 2016 January a large number of dust clouds appeared that had an orbital period of 4.4912 hours, and this event also marked the end of a 3-month interval dominated by the K2 `A' period. The second event was a 2016 April 21 appearance of four dip features with drift lines in a waterfall diagram (date vs. phase) that diverged from their origin date, at a location away from the `A' asteroid, and which lasted for two weeks. The third event was the sudden appearance of a dip feature with a period of 4.6064 hours, which is essentially the same as the K2 `B' period. The evolution of dip shape, depth, and total fade amount provide constraints on dust production and loss mechanisms. Collisions can account for the sudden appearance of dust clouds, and the sudden increase in dust amount, but another mechanism for continual dust production is also required.

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arXiv2016

K2-99: a subgiant hosting a transiting warm Jupiter in an eccentric orbit and a long-period companion

We report the discovery from K2 of a transiting planet in an 18.25-d, eccentric (0.19$\pm$ 0.04) orbit around K2-99, an 11th magnitude subgiant in Virgo. We confirm the planetary nature of the companion with radial velocities, and determine that the star is a metal-rich ([Fe/H] = 0.20$\pm$0.05) subgiant, with mass $1.60^{+0.14}_{-0.10}~M_\odot$ and radius $3.1\pm 0.1~R_\odot$. The planet has a mass of $0.97\pm0.09~M_{\rm Jup}$ and a radius $1.29\pm0.05~R_{\rm Jup}$. A measured systemic radial acceleration of $-2.12\pm0.04~{\rm m s^{-1} d^{-1}}$ offers compelling evidence for the existence of a third body in the system, perhaps a brown dwarf orbiting with a period of several hundred days.

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arXiv2016

Gray transits of WD 1145+017 over the visible band

We have observed several relatively deep transits of the white dwarf WD 1145+017 with the GTC over the wavelength range 480 nm to 920 nm. The observations covered approximately one hour on 2016 Jan 18 and two hours on 2016 Jan 20. There was variable extinction of the white dwarf during much of that time, but punctuated by four sharp transits with depths ranging from 25% to 40%. The spectrum was dispersed with a grism, and the flux data were ultimately summed into four bands centered at 0.53, 0.62, 0.71, and 0.84 $μ$m. After careful normalization, we find that the flux light curves in all four bands are consistent with being the same, including through the deepest dips. We use these results to compute Ångström exponents, $α$, for the particles responsible for the extinction and find |$\langle α\rangle $| $\lesssim 0.06$, assuming that the extinction is relatively optically thin. We use the complex indices of refraction for common minerals to set constraints on the median sizes of possible dust grains, and find that for most common minerals, particle sizes $\lesssim 0.5 \, μ$m can be excluded.

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arXiv2016

The GTC exoplanet transit spectroscopy survey. IV.: No asymmetries in the transit of Corot-29b

Context. The launch of the exoplanet space missions obtaining exquisite photometry from space has resulted in the discovery of thousands of planetary systems with very different physical properties and architectures. Among them, the exoplanet CoRoT-29b was identified in the light curves the mission obtained in summer 2011, and presented an asymmetric transit light curve, which was tentatively explained via the effects of gravity darkening. Aims. Transits of CoRoT-29b are measured with precision photometry, to characterize the reported asymmetry in their transit shape. Methods. Using the OSIRIS spectrograph at the 10-m GTC telescope, we perform spectro-photometric differential observations, which allow us to both calculate a high-accuracy photometric light curve, and a study of the color-dependence of the transit. Results. After careful data analysis, we find that the previously reported asymmetry is not present in either of two transits, observed in July 2014 and July 2015 with high photometric precisions of 300ppm over 5 minutes. Due to the relative faintness of the star, we do not reach the precision necessary to perform transmission spectroscopy of its atmosphere, but we see no signs of color-dependency of the transit depth or duration. Conclusions. We conclude that the previously reported asymmetry may have been a time-dependent phenomenon, which did not occur in more recent epochs. Alternatively, instrumental effects in the discovery data may need to be reconsidered.

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arXiv2015

An eclipsing double-line spectroscopic binary at the stellar/substellar boundary in the Upper Scorpius OB association

We aim at constraining evolutionary models at low mass and young ages by identifying interesting transiting system members of the nearest OB association to the Sun, Upper Scorpius, targeted by the Kepler mission. We produced light curves for M dwarf members of the USco region surveyed during the second campaign of the Kepler K2 mission. We identified 'by eye' a transiting system, UScoJ161630.68-251220.1 (=EPIC203710387) with a combined spectral type of M5.25 whose photometric, astrometric, and spectroscopic properties makes it a member of USco. We conducted an extensive photometric and spectroscopic follow-up of this transiting system with a suite of telescopes and instruments to characterise the properties of each component of the system. We calculated a transit duration of about 2.42 hours occuring every 2.88 days with a slight difference in transit depth and phase between the two components. We estimated a mass ratio of 0.922+/-0.015 from the semi-amplitudes of the radial velocity curves for each component. We derived masses of 0.091+/-0.005 Msun and 0.084+/-0.004 Msun,radii of 0.388+/-0.008 Rsun and 0.380+/-0.008 Rsun, luminosities of log(L/Lsun)=-2.020 (-0.121+0.099) dex and -2.032 (-0.121+0.099) dex, and effective temperatures of 2901 (-172+199) K and 2908 (-172+199) K for the primary and secondary, respectively. We present a complete photometric and radial velocity characterisation of the least massive double-line eclipsing binary system in the young USco association with two components close to the stellar/substellar limit. This system fills in a gap between the least massive eclipsing binaries in the low-mass and substellar regimes at young ages and represents an important addition to constrain evolutionary models at young ages.

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arXiv2015

The HARPS search for southern extra-solar planets. XXXVIII. Bayesian re-analysis of three systems. New super-Earths, unconfirmed signals, and magnetic cycles

We present the analysis of the entire HARPS observations of three stars that host planetary systems: HD1461, HD40307, and HD204313. The data set spans eight years and contains more than 200 nightly averaged velocity measurements for each star. This means that it is sensitive to both long-period and low-mass planets and also to the effects induced by stellar activity cycles. We modelled the data using Keplerian functions that correspond to planetary candidates and included the short- and long-term effects of magnetic activity. A Bayesian approach was taken both for the data modelling, which allowed us to include information from activity proxies such as $\log{(R'_{\rm HK})}$ in the velocity modelling, and for the model selection, which permitted determining the number of significant signals in the system. The Bayesian model comparison overcomes the limitations inherent to the traditional periodogram analysis. We report an additional super-Earth planet in the HD1461 system. Four out of the six planets previously reported for HD40307 are confirmed and characterised. We discuss the remaining two proposed signals. In particular, we show that when the systematic uncertainty associated with the techniques for estimating model probabilities are taken into account, the current data are not conclusive concerning the existence of the habitable-zone candidate HD40307 g. We also fully characterise the Neptune-mass planet that orbits HD204313 in 34.9 days.

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arXiv2015

HD144548: A young triply eclipsing system in the Upper Scorpius OB association

The star HD144548 (=HIP~78977; TYP~6212-1273-1) has been known as a detached eclipsing binary and a bona-fide member of the Upper Scorpius OB association. Continuous photometry from the K2 mission on Campaign Two has revealed the presence of additional eclipses due to the presence of a third star in the system. These are explained by a system composed of the two previously known members of the eclipsing system (Ba and Bb) with a period of 1.63 d, orbiting around an F7-F8V star with a period of 33.945 +/- 0.002 d in an eccentric orbit (e_A = 0.2652 +/- 0.0003). The timing of the eclipses of Ba and Bb reveals the same 33.9 d periodicity, which we interpret as the combination of a light time effect combined with dynamical perturbations on the close system. Here we combine radial velocities and analytical approximations for the timing of the eclipses to derive masses and radii for the three components of the system. We obtain a mass of 1.44 +/- 0.04 M_sun and radius of 2.41 +/- 0.03 R_sun for the A component, and almost identical masses and radii of about 0.96 M_sun and 1.33 R_sun for each of the two components of the close binary. HD144548 is the first triply eclipsing system for which radial velocities of all components could be measured.

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arXiv2015

Further constraints on the optical transmission spectrum of HAT-P-1b

We report on novel observations of HAT-P-1 aimed at constraining the optical transmission spectrum of the atmosphere of its transiting Hot-Jupiter exoplanet. Ground-based differential spectrophotometry was performed over two transit windows using the DOLORES spectrograph at the Telescopio Nazionale Galileo (TNG). Our measurements imply an average planet to star radius ratio equal to $\rm R_p/R_{\star}$=(0.1159$\pm$0.0005). This result is consistent with the value obtained from recent near infrared measurements of this object but differs from previously reported optical measurements being lower by around 4.4 exoplanet scale heights. Analyzing the data over 5 different spectral bins 600Å$\,$ wide we observed a single peaked spectrum (3.7 $\rmσ$ level) with a blue cut-off corresponding to the blue edge of the broad absorption wing of sodium and an increased absorption in the region in between 6180-7400Å. We also infer that the width of the broad absorption wings due to alkali metals is likely narrower than the one implied by solar abundance clear atmospheric models. We interpret the result as evidence that HAT-P-1b has a partially clear atmosphere at optical wavelengths with a more modest contribution from an optical absorber than previously reported.

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arXiv2015

Transiting exoplanets from the CoRoT space mission XXVIII. CoRoT-33b, an object in the brown dwarf desert with 2:3 commensurability with its host star

We report the detection of a rare transiting brown dwarf with a mass of 59 M_Jup and radius of 1.1 R_Jup around the metal-rich, [Fe/H] = +0.44, G9V star CoRoT-33. The orbit is eccentric (e = 0.07) with a period of 5.82 d. The companion, CoRoT-33b, is thus a new member in the so-called brown dwarf desert. The orbital period is within 3% to a 3:2 resonance with the rotational period of the star. CoRoT-33b may be an important test case for tidal evolution studies. The true frequency of brown dwarfs close to their host stars (P < 10 d) is estimated to be approximately 0.2% which is about six times smaller than the frequency of hot Jupiters in the same period range. We suspect that the frequency of brown dwarfs declines faster with decreasing period than that of giant planets.

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arXiv2015

Transiting exoplanets from the CoRoT space mission XXVII. CoRoT-28b, a planet orbiting an evolved star, and CoRoT-29b, a planet showing an asymmetric transit

Context. We present the discovery of two transiting extrasolar planets by the satellite CoRoT. Aims. We aim at a characterization of the planetary bulk parameters, which allow us to further investigate the formation and evolution of the planetary systems and the main properties of the host stars. Methods. We used the transit light curve to characterize the planetary parameters relative to the stellar parameters. The analysis of HARPS spectra established the planetary nature of the detections, providing their masses. Further photometric and spectroscopic ground-based observations provided stellar parameters (log g,Teff,v sin i) to characterize the host stars. Our model takes the geometry of the transit to constrain the stellar density into account, which when linked to stellar evolutionary models, determines the bulk parameters of the star. Because of the asymmetric shape of the light curve of one of the planets, we had to include the possibility in our model that the stellar surface was not strictly spherical. Results. We present the planetary parameters of CoRoT-28b, a Jupiter-sized planet (mass 0.484+/-0.087MJup; radius 0.955+/-0.066RJup) orbiting an evolved star with an orbital period of 5.208 51 +/- 0.000 38 days, and CoRoT-29b, another Jupiter-sized planet (mass 0.85 +/- 0.20MJup; radius 0.90 +/- 0.16RJup) orbiting an oblate star with an orbital period of 2.850 570 +/- 0.000 006 days. The reason behind the asymmetry of the transit shape is not understood at this point. Conclusions. These two new planetary systems have very interesting properties and deserve further study, particularly in the case of the star CoRoT-29.

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arXiv2015

Kepler423b: a half-Jupiter mass planet transiting a very old solar-like star

We report the spectroscopic confirmation of the Kepler object of interest KOI-183.01 (Kepler-423b), a half-Jupiter mass planet transiting an old solar-like star every 2.7 days. Our analysis is the first to combine the full Kepler photometry (quarters 1-17) with high-precision radial velocity measurements taken with the FIES spectrograph at the Nordic Optical Telescope. We simultaneously modelled the photometric and spectroscopic data-sets using Bayesian approach coupled with Markov chain Monte Carlo sampling. We found that the Kepler pre-search data conditioned (PDC) light curve of KOI-183 exhibits quarter-to-quarter systematic variations of the transit depth, with a peak-to-peak amplitude of about 4.3 % and seasonal trends reoccurring every four quarters. We attributed these systematics to an incorrect assessment of the quarterly variation of the crowding metric. The host star KOI-183 is a G4 dwarf with $M_\star=0.85\pm0.04$ M$_\rm{Sun}$, $R_\star=0.95\pm0.04$ R$_\rm{Sun}$, $T_\mathrm{eff}=5560\pm80$ K, $[M/H]=-0.10\pm0.05$ dex, and with an age of $11\pm2$ Gyr. The planet KOI-183b has a mass of $M_\mathrm{p}=0.595\pm0.081$ M$_\mathrm{Jup}$ and a radius of $R_\mathrm{p}=1.192\pm0.052$ R$_\mathrm{Jup}$, yielding a planetary bulk density of $ρ_\mathrm{p}=0.459\pm0.083$ g/cm$^{3}$. The radius of KOI-183b is consistent with both theoretical models for irradiated coreless giant planets and expectations based on empirical laws. The inclination of the stellar spin axis suggests that the system is aligned along the line of sight. We detected a tentative secondary eclipse of the planet at a 2-$σ$ confidence level ($ΔF_{\mathrm{ec}}=14.2\pm6.6$ ppm) and found that the orbit might have a small non-zero eccentricity of $e=0.019^{+0.028}_{-0.014}$. With a Bond albedo of $A_\mathrm{B}=0.037\pm0.019$, KOI-183b is one of the gas-giant planets with the lowest albedo known so far.

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arXiv2014

SOPHIE velocimetry of Kepler transit candidates XII. KOI-1257 b: a highly eccentric three-month period transiting exoplanet

In this paper we report a new transiting warm giant planet: KOI-1257 b. It was first detected in photometry as a planet-candidate by the ${\it Kepler}$ space telescope and then validated thanks to a radial velocity follow-up with the SOPHIE spectrograph. It orbits its host star with a period of 86.647661 d $\pm$ 3 s and a high eccentricity of 0.772 $\pm$ 0.045. The planet transits the main star of a metal-rich, relatively old binary system with stars of mass of 0.99 $\pm$ 0.05 Msun and 0.70 $ \pm $ 0.07 Msun for the primary and secondary, respectively. This binary system is constrained thanks to a self-consistent modelling of the ${\it Kepler}$ transit light curve, the SOPHIE radial velocities, line bisector and full-width half maximum (FWHM) variations, and the spectral energy distribution. However, future observations are needed to confirm it. The PASTIS fully-Bayesian software was used to validate the nature of the planet and to determine which star of the binary system is the transit host. By accounting for the dilution from the binary both in photometry and in radial velocity, we find that the planet has a mass of 1.45 $ \pm $ 0.35 Mjup, and a radius of 0.94 $ \pm $ 0.12 Rjup, and thus a bulk density of 2.1 $ \pm $ 1.2 g.cm$^{-3}$. The planet has an equilibrium temperature of 511 $\pm$ 50 K, making it one of the few known members of the warm-jupiter population. The HARPS-N spectrograph was also used to observe a transit of KOI-1257 b, simultaneously with a joint amateur and professional photometric follow-up, with the aim of constraining the orbital obliquity of the planet. However, the Rossiter-McLaughlin effect was not clearly detected, resulting in poor constraints on the orbital obliquity of the planet.

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arXiv2014

CoRoT-22 b: a validated 4.9 RE exoplanet in 10-day orbit

The CoRoT satellite has provided high-precision photometric light curves for more than 163,000 stars and found several hundreds of transiting systems compatible with a planetary scenario. If ground-based velocimetric observations are the best way to identify the actual planets among many possible configurations of eclipsing binary systems, recent transit surveys have shown that it is not always within reach of the radial-velocity detection limits. In this paper, we present a transiting exoplanet candidate discovered by CoRoT whose nature cannot be established from ground-based observations, and where extensive analyses are used to validate the planet scenario. They are based on observing constraints from radial-velocity spectroscopy, adaptive optics imaging and the CoRoT transit shape, as well as from priors on stellar populations, planet and multiple stellar systems frequency. We use the fully Bayesian approach developed in the PASTIS analysis software, and conclude that the planet scenario is at least 1400 times more probable than any other false positive scenario. The primary star is a metallic solar-like dwarf, with Ms = 1.099+-0.049 Msun and Rs = 1.136 (+0.038,-0.090) Rsun . The validated planet has a radius of Rp = 4.88 (+0.17,-0.39) RE and mass less than 49 ME. Its mean density is smaller than 2.56 g/cm^3 and orbital period is 9.7566+-0.0012 days. This object, called CoRoT-22 b, adds to a large number of validated Kepler planets. These planets do not have a proper measurement of the mass but allow statistical characterization of the exoplanet population.

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arXiv2014

Revisiting the transits of CoRoT-7b at a lower activity level

CoRoT-7b, the first super-Earth with measured radius discovered, has opened the new field of rocky exoplanets characterisation. To better understand this interesting system, new observations were taken with the CoRoT satellite. During this run 90 new transits were obtained in the imagette mode. These were analysed together with the previous 151 transits obtained in the discovery run and HARPS radial velocity observations to derive accurate system parameters. A difference is found in the posterior probability distribution of the transit parameters between the previous CoRoT run (LRa01) and the new run (LRa06). We propose this is due to an extra noise component in the previous CoRoT run suspected to be transit spot occultation events. These lead to the mean transit shape becoming V-shaped. We show that the extra noise component is dominant at low stellar flux levels and reject these transits in the final analysis. We obtained a planetary radius, $R_p= 1.585\pm0.064\,R_{\oplus}$, in agreement with previous estimates. Combining the planetary radius with the new mass estimates results in a planetary density of $ 1.19 \pm 0.27\, ρ_{\oplus}$ which is consistent with a rocky composition. The CoRoT-7 system remains an excellent test bed for the effects of activity in the derivation of planetary parameters in the shallow transit regime.

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arXiv2014

Transiting exoplanets from the CoRoT space mission: XXVI. CoRoT-24: A transiting multi-planet system

We present the discovery of a candidate multiply-transiting system, the first one found in the CoRoT mission. Two transit-like features with periods of 5.11 and 11.76d are detected in the CoRoT light curve, around a main sequence K1V star of r=15.1. If the features are due to transiting planets around the same star, these would correspond to objects of 3.7$\pm$0.4 and 5.0$\pm$0.5 R_earth respectively. Several radial velocities serve to provide an upper limit of 5.7 M_earth for the 5.11~d signal, and to tentatively measure a mass of 28$^{+11}_{-11}$ M_earth for the object transiting with a 11.76~d period. These measurements imply low density objects, with a significant gaseous envelope. The detailed analysis of the photometric and spectroscopic data serve to estimate the probability that the observations are caused by transiting Neptune-sized planets as $>$26$\times$ higher than a blend scenario involving only one transiting planet, and $>$900$\times$ higher than a scenario involving two blends and no planets. The radial velocities show a long term modulation that might be attributed to a 1.5 M_jup planet orbiting at 1.8~A.U. from the host, but more data are required to determine the precise orbital parameters of this companion.

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arXiv2014

Confirmation of an exoplanet using the transit color signature: Kepler-418b, a blended giant planet in a multiplanet system

We announce confirmation of Kepler-418b, one of two proposed planets in this system. This is the first confirmation of an exoplanet based primarily on the transit color signature technique. We used the Kepler public data archive combined with multicolor photometry from the Gran Telescopio de Canarias and radial velocity follow-up using FIES at the Nordic Optical Telescope for confirmation. We report a confident detection of a transit color signature that can only be explained by a compact occulting body, entirely ruling out a contaminating eclipsing binary, a hierarchical triple, or a grazing eclipsing binary. Those findings are corroborated by our radial velocity measurements, which put an upper limit of ~1 Mjup on the mass of Kepler-418b. We also report that the host star is significantly blended, confirming the ~10% light contamination suspected from the crowding metric in the Kepler light curve measured by the Kepler team. We report detection of an unresolved light source that contributes an additional ~40% to the target star, which would not have been detected without multicolor photometric analysis. The resulting planet-star radius ratio is 0.110 +/- 0.0025, more than 25% more than the 0.087 measured by Kepler, leading to a radius of 1.20 +/- 0.16 Rjup instead of the 0.94 Rjup measured by the Kepler team. This is the first confirmation of an exoplanet candidate based primarily on the transit color signature, demonstrating that this technique is viable from ground for giant planets. It is particularly useful for planets with long periods such as Kepler-418b, which tend to have long transit durations. Additionally, multicolor photometric analysis of transits can reveal unknown stellar neighbors and binary companions that do not affect the classification of the transiting object but can have a very significant effect on the perceived planetary radius.

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arXiv2014

Transiting exoplanets from the CoRoT space mission XXV. CoRoT-27b: a massive and dense planet on a short-period orbit

We report the discovery of a massive and dense transiting planet CoRoT-27b on a 3.58 day orbit around a 4.2 Gyr-old G2 star. The planet candidate was identified from the CoRoT photometry, and was confirmed as a planet with ground-based spectroscopy. The confirmation of the planet candidate is based on radial velocity observations combined with imaging to rule out blends. The characterisation of the planet and its host star is carried out using a Bayesian approach where all the data (CoRoT photometry, radial velocities, and spectroscopic characterisation of the star) are used jointly. The Bayesian analysis includes a study whether the assumption of white normally distributed noise holds for the CoRoT photometry, and whether the use of a non-normal noise distribution offers advantages in parameter estimation and model selection. CoRoT-27b has a mass of $10.39 \pm 0.55$ $\mathrm{M}_{\rm Jup}$, a radius of $1.01 \pm 0.04$ $\mathrm{R}_{\rm Jup}$, a mean density of $12.6_{-1.67}^{+1.92}$ $\mathrm{g\,cm^{-3}}$, and an effective temperature of $1500 \pm 130$ K. The planet orbits around its host star, a 4.2 Gyr-old G2-star with a mass $M_{\star}=1.06$ $M_{\odot}$, and a radius $R_{\star}=1.05$ $R_{\odot}$, on a $0.048 \pm 0.007$ AU orbit every 3.58 days. The radial velocity observations allow us to exclude highly eccentric orbits, namely, $e<0.065$ with a 99% confidence. Given its high mass and density, theoretical modelling of CoRoT-27b is demanding. We identify two solutions with heavy element mass fractions of $0.11\pm0.08$ $\mathrm{M_{\oplus}}$ and $0.07\pm0.06$ $\mathrm{M_{\oplus}}$, but even solutions void of heavy elements cannot be excluded. We carry out a secondary eclipse search from the CoRoT photometry using a method based on Bayesian model selection, but conclude that the noise level is too high to detect eclipses shallower than 9% of the transit depth.

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arXiv2013

Neutrino and Charged Lepton Flavour Today

Flavour physics is a priceless window on physics beyond the Standard Model. In particular, flavour violation in the lepton sector looks very promising, as high precision measurements are prospected in future experiments investigating on $μ\rightarrow e$ conversion in atomic nuclei: the predictions for this observable are analysed in the context of the type I Seesaw mechanism. Furthermore, new ideas to explain the Flavour Puzzle recently appeared, mainly based on a possible dynamical origin of the Yukawa couplings and on flavour symmetries. The focus of this proceeding will be set on the Minimal Flavour Violation ansatz and on the role of the neutrino Majorana character: when an $O(2)_{N}$ flavour symmetry acts on the right-handed neutrino sector, the minimum of the scalar potential allows for large mixing angles -in contrast to the simplest quark case- and predicts a maximal Majorana phase. This leads to a strong correlation between neutrino mass hierarchy and mixing pattern.

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