arXiv subjects

J. C. Morales

Publications and source records attributed to J. C. Morales.

At least 109 records · Page 6Linked to original sources

arXiv2018

Detection and characterization of an ultra-dense sub-Neptune planet orbiting the Sun-like star HD 119130

We present the discovery and characterization of a new transiting planet from Campaign 17 of the Kepler extended mission K2. HD 119130 b is a warm sub-Neptune on a 17-d orbit around a bright (V = 9.9 mag) solar-like G3 V star with a mass and radius of $M_\star = 1.00\pm0.03\,\mathrm{M_\odot}$ and $R_\star = 1.09\pm0.03\,\mathrm{R_\odot}$, respectively. We model simultaneously the K2 photometry and CARMENES spectroscopic data and derive a radius of $R_\mathrm{p} = 2.63_{-0.10}^{+0.12}\,\mathrm{R_\oplus}$ and mass of $M_\mathrm{p} = 24.5_{-4.4}^{+4.4}\,\mathrm{M_\oplus}$, yielding a mean density of $ρ_\mathrm{p} = 7.4_{-1.5}^{+1.6}\,\mathrm{g\,cm^{-3}}$, which makes it one of the densest sub-Neptune planets known to date. We also detect a linear trend in radial velocities of HD 119130 ($\dotγ_{\rm RV}= -0.40^{+0.07}_{-0.07}\,\mathrm{m\,s^{-1}\,d^{-1}}$) that suggests a long-period companion with a minimum mass on the order of $33\,\mathrm{M_\oplus}$. If confirmed, it would support a formation scenario of HD 119130 b by migration caused by Kozai-Lidov oscillations.

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arXiv2018

Detection of He I $\lambda10830$ Å absorption on HD 189733 b with CARMENES high-resolution transmission spectroscopy

We present three transit observations of HD 189733 b obtained with the high-resolution spectrograph CARMENES at Calar Alto. A strong absorption signal is detected in the near-infrared He I triplet at 10830 Å in all three transits. During mid-transit, the mean absorption level is $0.88\pm0.04$ % measured in a $\pm$10 km s$^{-1}$ range at a net blueshift of $-3.5\pm0.4$ km s$^{-1}$ (10829.84--10830.57 Å). The absorption signal exhibits radial velocities of $+6.5\pm3.1$ km s$^{-1}$ and $-12.6\pm1.0$ km s$^{-1}$ during ingress and egress, respectively; measured in the planetary rest frame. We show that stellar activity related pseudo-signals interfere with the planetary atmospheric absorption signal. They could contribute as much as 80% of the observed signal and might also affect the radial velocity signature, but pseudo-signals are very unlikely to explain the entire signal. The observed line ratio between the two unresolved and the third line of the He I triplet is $2.8\pm0.2$, which strongly deviates from the value expected for an optically thin atmospheres. When interpreted in terms of absorption in the planetary atmosphere, this favors a compact helium atmosphere with an extent of only 0.2 planetary radii and a substantial column density on the order of $4\times 10^{12}$ cm$^{-2}$. The observed radial velocities can be understood either in terms of atmospheric circulation with equatorial superrotation or as a sign of an asymmetric atmospheric component of evaporating material. We detect no clear signature of ongoing evaporation, like pre- or post-transit absorption, which could indicate material beyond the planetary Roche lobe, or radial velocities in excess of the escape velocity. These findings do not contradict planetary evaporation, but only show that the detected helium absorption in HD 189733 b does not trace the atmospheric layers that show pronounced escape signatures.

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arXiv2018

A candidate super-Earth planet orbiting near the snow line of Barnard's star

At a distance of 1.8 parsecs, Barnard's star (Gl 699) is a red dwarf with the largest apparent motion of any known stellar object. It is the closest single star to the Sun, second only to the alpha Centauri triple stellar system. Barnard's star is also among the least magnetically active red dwarfs known and has an estimated age older than our Solar System. Its properties have made it a prime target for planet searches employing techniques such as radial velocity, astrometry, and direct imaging, all with different sensitivity limits but ultimately leading to disproved or null results. Here we report that the combination of numerous measurements from high-precision radial velocity instruments reveals the presence of a low-amplitude but significant periodic signal at 233 days. Independent photometric and spectroscopic monitoring, as well as the analysis of instrumental systematic effects, show that this signal is best explained as arising from a planetary companion. The candidate planet around Barnard's star is a cold super-Earth with a minimum mass of 3.2 Earth masses orbiting near its snow-line. The combination of all radial velocity datasets spanning 20 years additionally reveals a long-term modulation that could arise from a magnetic activity cycle or from a more distant planetary object. Because of its proximity to the Sun, the proposed planet has a maximum angular separation of 220 milli-arcseconds from Barnard's star, making it an excellent target for complementary direct imaging and astrometric observations.

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arXiv2018

Multiple water band detections in the CARMENES near-infrared transmission spectrum of HD 189733 b

Aims: We explore the capabilities of CARMENES for characterizing hot-Jupiter atmospheres by targeting multiple water bands, in particular, those at 1.15 and 1.4 $μ$m. Hubble Space Telescope observations suggest that this wavelength region is relevant for distinguishing between hazy/cloudy and clear atmospheres. Methods: We observed one transit of the hot Jupiter HD 189733 b with CARMENES. Telluric and stellar absorption lines were removed using Sysrem, which performs a principal component analysis including proper error propagation. The residual spectra were analysed for water absorption with cross-correlation techniques using synthetic atmospheric absorption models. Results: We report a cross-correlation peak at a signal-to-noise ratio (SNR) of 6.6, revealing the presence of water in the transmission spectrum of HD 189733 b. The absorption signal appeared slightly blueshifted at -3.9 $\pm$ 1.3 kms$^{-1}$. We measured the individual cross-correlation signals of the water bands at 1.15 and 1.4 $μ$m, finding cross-correlation peaks at SNRs of 4.9 and 4.4, respectively. The 1.4 $μ$m feature is consistent with that observed with the Hubble Space Telescope. Conclusions: The water bands studied in this work have been mainly observed in a handful of planets from space. The ability of also detecting them individually from the ground at higher spectral resolution can provide insightful information to constrain the properties of exoplanet atmospheres. Although the current multiband detections can not yet constrain atmospheric haze models for HD 189733 b, future observations at higher signal-to-noise ratio could provide an alternative way to achieve this aim.

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arXiv2018

The CARMENES search for exoplanets around M dwarfs: The warm super-Earths in twin orbits around the mid-type M dwarfs Ross 1020 (GJ 3779) and LP 819-052 (GJ 1265)

We announce the discovery of two planetary companions orbiting around the low mass stars Ross 1020 (GJ 3779, M4.0V) and LP 819-052 (GJ 1265, M4.5V). The discovery is based on the analysis of CARMENES radial velocity observations in the visual channel as part of its survey for exoplanets around M dwarfs. In the case of GJ 1265, CARMENES observations were complemented with publicly available Doppler measurements from HARPS. The datasets reveal one planetary companion for each star that share very similar properties: minimum masses of $8.0\pm0.5$ M$_{\oplus}$ and $7.4\pm0.5$ M$_{\oplus}$ in low-eccentricity orbits with periods of $3.023\pm0.001$ d and $3.651\pm0.001$ d for GJ 3779 b and GJ 1265 b, respectively. The periodic signals around three days found in the radial velocity data have no counterpart in any spectral activity indicator. Besides, we collected available photometric data for the two host stars, which confirm that the additional Doppler variations found at periods around 95 d can be attributed to the rotation of the stars. The addition of these planets in a mass-period diagram of known planets around M dwarfs suggests a bimodal distribution with a lack of short-period low-mass planets in the range of 2-5 M$_{\oplus}$. It also indicates that super-Earths (> 5 M$_{\oplus}$) currently detected by radial velocity and transit techniques around M stars are usually found in systems dominated by a single planet.

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arXiv2018

The CARMENES search for exoplanets around M dwarfs: Nine new double-line spectroscopic binary stars

Context. The CARMENES spectrograph is surveying ~300 M dwarf stars in search for exoplanets. Among the target stars, spectroscopic binary systems have been discovered, which can be used to measure fundamental properties of stars. Aims. Using spectroscopic observations, we determine the orbital and physical properties of nine new double-line spectroscopic binary systems by analysing their radial velocity curves. Methods. We use two-dimensional cross-correlation techniques to derive the radial velocities of the targets, which are then employed to determine the orbital properties. Photometric data from the literature are also analysed to search for possible eclipses and to measure stellar variability, which can yield rotation periods. Results. Out of the 342 stars selected for the CARMENES survey, 9 have been found to be double-line spectroscopic binaries, with periods ranging from 1.13 to ~8000 days and orbits with eccentricities up to 0.54. We provide empirical orbital properties and minimum masses for the sample of spectroscopic binaries. Absolute masses are also estimated from mass-luminosity calibrations, ranging between ~0.1 and ~0.6 Msol . Conclusions. These new binary systems increase the number of double-line M dwarf binary systems with known orbital parameters by 15%, and they have lower mass ratios on average.

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arXiv2018

The CARMENES search for exoplanets around M dwarfs. A Neptune-mass planet traversing the habitable zone around HD 180617

Despite their activity, low-mass stars are of particular importance for the search of exoplanets by the means of Doppler spectroscopy, as planets with lower masses become detectable. We report on the discovery of a planetary companion around HD 180617, a bright J = 5.58 mag, low-mass M = 0.45 M_{sun} star of spectral type M2.5 V. The star, located at a distance of 5.9 pc, is the primary of the high proper motion binary system containing vB 10, a star with one of the lowest masses known in most of the twentieth century. Our analysis is based on new radial velocity (RV) measurements made at red-optical wavelengths provided by the high-precision spectrograph CARMENES, which was designed to carry out a survey for Earth-like planets around M dwarfs. The available CARMENES data are augmented by archival Doppler measurements from HIRES and HARPS. Altogether, the RVs span more than 16 years. The modeling of the RV variations, with a semi-amplitude of K = 2.85-0.25/+0.16m/s yields a Neptune-like planet with a minimum mass of 12.2-1.4/+1.0 M_{Earth} on a 105.90-0.10/+0.09d circumprimary orbit, which is partly located in the host star's habitable zone. The analysis of time series of common activity indicators does not show any dependence on the detected RV signal. The discovery of HD 180617 b not only adds information to a currently hardly filled region of the mass-period diagram of exoplanets around M dwarfs, but the investigated system becomes the third known binary consisting of M dwarfs and hosting an exoplanet in an S-type configuration. Its proximity makes it an attractive candidate for future studies.

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arXiv2018

Detection and Doppler monitoring of EPIC 246471491, a system of four transiting planets smaller than Neptune

The Kepler extended mission, also known as K2, has provided the community with a wealth of planetary candidates that orbit stars typically much brighter than the targets of the original mission. These planet candidates are suitable for further spectroscopic follow-up and precise mass determinations, leading ultimately to the construction of empirical mass-radius diagrams. Particularly interesting is to constrain the properties of planets between the Earth and Neptune in size, the most abundant type of planets orbiting Sun-like stars with periods less than a few years. Among many other K2 candidates, we discovered a multi-planetary system around EPIC246471491, with four planets ranging in size from twice the size of Earth, to nearly the size of Neptune. We measure the mass of the planets of the EPIC246471491 system by means of precise radial velocity measurements using the CARMENES spectrograph and the HARPS-N spectrograph. With our data we are able to determine the mass of the two inner planets of the system with a precision better than 15%, and place upper limits on the masses of the two outer planets. We find that EPIC246471491b has a mass of 9.68 Me, and a radius of 2.59 Re, yielding a mean density of 3.07 g/cm3, while EPIC246471491c has a mass of 15.68 Me, radius of 3.53 Re, and a mean density of 19.5 g/cm3. For EPIC246471491d (R=2.48Re) and EPIC246471491e (R=1.95Re) the upper limits for the masses are 6.5 and 10.7 Me, respectively. The system is thus composed of a nearly Neptune-twin planet (in mass and radius), two sub-Neptunes with very different densities and presumably bulk composition, and a fourth planet in the outermost orbit that resides right in the middle of the super-Earth/sub-Neptune radius gap. Future comparative planetology studies of this system can provide useful insights into planetary formation, and also a good test of atmospheric escape and evolution theories.

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arXiv2018

Efficient scheduling of astronomical observations. Application to the CARMENES radial-velocity survey

Targeted spectroscopic exoplanet surveys face the challenge of maximizing their planet detection rates by means of careful planning. The number of possible observation combinations for a large exoplanet survey, i.e., the sequence of observations night after night, both in total time and amount of targets, is enormous. Sophisticated scheduling tools and the improved understanding of the exoplanet population are employed to investigate an efficient and optimal way to plan the execution of observations. This is applied to the CARMENES instrument, which is an optical and infrared high-resolution spectrograph that has started a survey of about 300 M-dwarf stars in search for terrestrial exoplanets. We use evolutionary computation techniques to create an automatic scheduler that minimizes the idle periods of the telescope and that distributes the observations among all the targets using configurable criteria. We simulate the case of the CARMENES survey with a realistic sample of targets, and we estimate the efficiency of the planning tool both in terms of telescope operations and planet detection. Our scheduling simulations produce plans that use about 99$\%$ of the available telescope time (including overheads) and optimally distribute the observations among the different targets. Under such conditions, and using current planet statistics, the optimized plan using this tool should allow the CARMENES survey to discover about 65$\%$ of the planets with radial-velocity semi-amplitudes greater than 1$~m\thinspace s^{-1}$ when considering only photon noise. The simulations using our scheduling tool show that it is possible to optimize the survey planning by minimizing idle instrument periods and fulfilling the science objectives in an efficient manner to maximize the scientific return.

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arXiv2018

The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra

Previous simulations predicted the activity-induced radial-velocity (RV) variations of M dwarfs to range from $\sim1$ cm/s to $\sim1$ km/s, depending on various stellar and activity parameters. We investigate the observed relations between RVs, stellar activity, and stellar parameters of M dwarfs by analyzing CARMENES high-resolution visual-channel spectra ($0.5$$-$$1$$μ$m), which were taken within the CARMENES RV planet survey during its first $20$ months of operation. During this time, $287$ of the CARMENES-sample stars were observed at least five times. From each spectrum we derived a relative RV and a measure of chromospheric H$α$ emission. In addition, we estimated the chromatic index (CRX) of each spectrum, which is a measure of the RV wavelength dependence. Despite having a median number of only $11$ measurements per star, we show that the RV variations of the stars with RV scatter of $>10$ m/s and a projected rotation velocity $v \sin{i}>2$ km/s are caused mainly by activity. We name these stars `active RV-loud stars' and find their occurrence to increase with spectral type: from $\sim3\%$ for early-type M dwarfs (M$0.0$$-$$2.5$V) through $\sim30\%$ for mid-type M dwarfs (M$3.0$$-$$5.5$V) to $>50\%$ for late-type M dwarfs (M$6.0$$-$$9.0$V). Their RV-scatter amplitude is found to be correlated mainly with $v \sin{i}$. For about half of the stars, we also find a linear RV$-$CRX anticorrelation, which indicates that their activity-induced RV scatter is lower at longer wavelengths. For most of them we can exclude a linear correlation between RV and H$α$ emission. Our results are in agreement with simulated activity-induced RV variations in M dwarfs. The RV variations of most active RV-loud M dwarfs are likely to be caused by dark spots on their surfaces, which move in and out of view as the stars rotate.

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arXiv2018

The CARMENES search for exoplanets around M dwarfs: High-resolution optical and near-infrared spectroscopy of 324 survey stars

The CARMENES radial velocity (RV) survey is observing 324 M dwarfs to search for any orbiting planets. In this paper, we present the survey sample by publishing one CARMENES spectrum for each M dwarf. These spectra cover the wavelength range 520--1710nm at a resolution of at least $R > 80,000$, and we measure its RV, H$α$ emission, and projected rotation velocity. We present an atlas of high-resolution M-dwarf spectra and compare the spectra to atmospheric models. To quantify the RV precision that can be achieved in low-mass stars over the CARMENES wavelength range, we analyze our empirical information on the RV precision from more than 6500 observations. We compare our high-resolution M-dwarf spectra to atmospheric models where we determine the spectroscopic RV information content, $Q$, and signal-to-noise ratio. We find that for all M-type dwarfs, the highest RV precision can be reached in the wavelength range 700--900nm. Observations at longer wavelengths are equally precise only at the very latest spectral types (M8 and M9). We demonstrate that in this spectroscopic range, the large amount of absorption features compensates for the intrinsic faintness of an M7 star. To reach an RV precision of 1ms$^{-1}$ in very low mass M dwarfs at longer wavelengths likely requires the use of a 10m class telescope. For spectral types M6 and earlier, the combination of a red visual and a near-infrared spectrograph is ideal to search for low-mass planets and to distinguish between planets and stellar variability. At a 4m class telescope, an instrument like CARMENES has the potential to push the RV precision well below the typical jitter level of 3-4ms$^{-1}$.

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arXiv2018

CARMENES input catalogue of M dwarfs: III. Rotation and activity from high-resolution spectroscopic observations

CARMENES is a spectrograph for radial velocity surveys of M dwarfs with the aim of detecting Earth-mass planets orbiting in the habitable zones of their host stars. To ensure an optimal use of the CARMENES Guaranteed Time Observations, in this paper we investigate the correlation of activity and rotation for approximately 2200 M dwarfs, ranging in spectral type from M0.0 V to M9.0 V. We present new high-resolution spectroscopic observations with FEROS, CAFE, and HRS of approximately 500 M dwarfs. For each new observation, we determined its radial velocity and measured its Halpha activity index and its rotation velocity. Additionally, we have multiple observations of many stars to investigate if there are any radial velocity variations due to multiplicity. The results of our survey confirm that early-M dwarfs are Halpha inactive with low rotational velocities and that late-M dwarfs are Halpha active with very high rotational velocities. The results of this high-resolution analysis comprise the most extensive catalogue of rotation and activity in M dwarfs currently available.

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arXiv2018

The CARMENES search for exoplanets around M dwarfs. First visual-channel radial-velocity measurements and orbital parameter updates of seven M-dwarf planetary systems

Context: The main goal of the CARMENES survey is to find Earth-mass planets around nearby M-dwarf stars. Seven M-dwarfs included in the CARMENES sample had been observed before with HIRES and HARPS and either were reported to have one short period planetary companion (GJ15A, GJ176, GJ436, GJ536 and GJ1148) or are multiple planetary systems (GJ581 and GJ876). Aims: We aim to report new precise optical radial velocity measurements for these planet hosts and test the overall capabilities of CARMENES. Methods: We combined our CARMENES precise Doppler measurements with those available from HIRES and HARPS and derived new orbital parameters for the systems. Bona-fide single planet systems are fitted with a Keplerian model. The multiple planet systems were analyzed using a self-consistent dynamical model and their best fit orbits were tested for long-term stability. Results: We confirm or provide supportive arguments for planets around all the investigated stars except for GJ15A, for which we find that the post-discovery HIRES data and our CARMENES data do not show a signal at 11.4 days. Although we cannot confirm the super-Earth planet GJ15Ab, we show evidence for a possible long-period ($P_{\rm c}$ = 7025$_{-629}^{+972}$ d) Saturn-mass ($m_{\rm c} \sin i$ = 51.8$_{-5.8}^{+5.5}M_\oplus$) planet around GJ15A. In addition, based on our CARMENES and HIRES data we discover a second planet around GJ1148, for which we estimate a period $P_{\rm c}$ = 532.6$_{-2.5}^{+4.1}$ d, eccentricity $e_{\rm c}$ = 0.34$_{-0.06}^{+0.05}$ and minimum mass $m_{\rm c} \sin i$ = 68.1$_{-2.2}^{+4.9}M_\oplus$. Conclusions: The CARMENES optical radial velocities have similar precision and overall scatter when compared to the Doppler measurements conducted with HARPS and HIRES. We conclude that CARMENES is an instrument that is up to the challenge of discovering rocky planets around low-mass stars.

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arXiv2017

HADES RV Programme with HARPS-N at TNG. VII. Rotation and activity of M-Dwarfs from time-series high-resolution spectroscopy of chromospheric indicators

We aim to investigate the presence of signatures of magnetic cycles and rotation on a sample of 71 early M-dwarfs from the HADES RV programme using high-resolution time-series spectroscopy of the Ca II H & K and Halpha chromospheric activity indicators, the radial velocity series, the parameters of the cross correlation function and the V-band photometry. We used mainly HARPS-N spectra, acquired over four years, and add HARPS spectra from the public ESO database and ASAS photometry light-curves as support data, extending the baseline of the observations of some stars up to 12 years. We provide log(R'hk) measurements for all the stars in the sample, cycle length measurements for 13 stars, rotation periods for 33 stars and we are able to measure the semi-amplitude of the radial velocity signal induced by rotation in 16 stars. We complement our work with previous results and confirm and refine the previously reported relationships between the mean level of chromospheric emission, measured by the log(R'hk), with the rotation period, and with the measured semi-amplitude of the activity induced radial velocity signal for early M-dwarfs. We searched for a possible relation between the measured rotation periods and the lengths of the magnetic cycle, finding a weak correlation between both quantities. Using previous v sin i measurements we estimated the inclinations of the star's poles to the line of sight for all the stars in the sample, and estimate the range of masses of the planets GJ 3998 b and c (2.5 - 4.9 Mearth and 6.3 - 12.5 Mearth), GJ 625 b (2.82 Mearth), GJ 3942 b (7.1 - 10.0 Mearth) and GJ 15A b (3.1 - 3.3 Mearth), assuming their orbits are coplanar with the stellar rotation.

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arXiv2017

The CARMENES search for exoplanets around M dwarfs - HD 147379b: A nearby Neptune in the temperate zone of an early-M dwarf

We report on the first star discovered to host a planet detected by radial velocity (RV) observations obtained within the CARMENES survey for exoplanets around M dwarfs. HD 147379 ($V = 8.9$ mag, $M = 0.58 \pm 0.08$ M$_{\odot}$), a bright M0.0V star at a distance of 10.7 pc, is found to undergo periodic RV variations with a semi-amplitude of $K = 5.1\pm0.4$ m s$^{-1}$ and a period of $P = 86.54\pm0.06$ d. The RV signal is found in our CARMENES data, which were taken between 2016 and 2017, and is supported by HIRES/Keck observations that were obtained since 2000. The RV variations are interpreted as resulting from a planet of minimum mass $m_{\rm p}\sin{i} = 25 \pm 2$ M$_{\oplus}$, 1.5 times the mass of Neptune, with an orbital semi-major axis $a = 0.32$ au and low eccentricity ($e < 0.13$). HD 147379b is orbiting inside the temperate zone around the star, where water could exist in liquid form. The RV time-series and various spectroscopic indicators show additional hints of variations at an approximate period of 21.1d (and its first harmonic), which we attribute to the rotation period of the star.

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arXiv2017

Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators

Context: The CARMENES survey is a high-precision radial velocity (RV) programme that aims to detect Earth-like planets orbiting low-mass stars. Aims: We develop least-squares fitting algorithms to derive the RVs and additional spectral diagnostics implemented in the SpEctrum Radial Velocity Analyser (SERVAL), a publicly available python code. Methods: We measured the RVs using high signal-to-noise templates created by coadding all available spectra of each star.We define the chromatic index as the RV gradient as a function of wavelength with the RVs measured in the echelle orders. Additionally, we computed the differential line width by correlating the fit residuals with the second derivative of the template to track variations in the stellar line width. Results: Using HARPS data, our SERVAL code achieves a RV precision at the level of 1m/s. Applying the chromatic index to CARMENES data of the active star YZ CMi, we identify apparent RV variations induced by stellar activity. The differential line width is found to be an alternative indicator to the commonly used full width half maximum. Conclusions: We find that at the red optical wavelengths (700--900 nm) obtained by the visual channel of CARMENES, the chromatic index is an excellent tool to investigate stellar active regions and to identify and perhaps even correct for activity-induced RV variations.

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arXiv2017

HADES RV Programme with HARPS-N at TNG VI. GJ 3942 b behind dominant activity signals

Short- to mid-term magnetic phenomena on the stellar surface of M-type stars cannot only resemble the effects of planets in radial velocity data, but also may hide them. We analyze 145 spectroscopic HARPS-N observations of GJ 3942 taken over the past five years and additional photometry to disentangle stellar activity effects from genuine Doppler signals as a result of the orbital motion of the star around the common barycenter with its planet. To achieve this, we use the common methods of pre-whitening, and treat the correlated red noise by a first-order moving average term and by Gaussian-process regression following an MCMC analysis. We identify the rotational period of the star at 16.3 days and discover a new super-Earth, GJ 3942 b, with an orbital period of 6.9 days and a minimum mass of 7.1 Me. An additional signal in the periodogram of the residuals is present but we cannot claim it to be related to a second planet with sufficient significance at this point. If confirmed, such planet candidate would have a minimum mass of 6.3 Me and a period of 10.4 days, which might indicate a 3:2 mean-motion resonance with the inner planet.

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arXiv2017

Combining Spitzer parallax and Keck II adaptive optics imaging to measure the mass of a solar-like star orbited by a cold gaseous planet discovered by microlensing

To obtain accurate mass measurements for cold planets discovered by microlensing, it is usually necessary to combine light curve modeling with at least two lens mass-distance relations. Often, a constraint on the Einstein ring radius measurement is obtained from the caustic crossing time: This is supplemented by secondary constraints such as precise parallax measurements and/or measures of the lens luminosity using high angular resolution observations. We resolved the source+lens star from sub-arcsecond blends in H band using adaptive optics (AO) observations with NIRC2 mounted on Keck II telescope. We identify additional flux, coincident with the source to within 160 mas. We estimate the potential contributions to this blended light (chance-aligned star, additional companion to the lens or to the source) and find that 85 % of of the NIR flux is due to the lens star at H_L=16.63 +- 0.06 and K_L=16.46 +- 0.06. We combined the parallax constraint and the AO constraint to derive the physical parameters of the system. The lensing system is composed of a mid-late type G main sequence star of M_L=0.89 +- 0.05 Mo located at D_L = 3.6 +- 0.3 kpc in the Galactic disk. Taking the mass ratio and projected separation from the original study leads to a planet of M_p= 0.64 +- 0.044 M_Jupiter at 3.48 +- 0.22 AU. Excellent parallax measurement from simultaneous ground-space observations have been obtained on the microlensing event OGLE-2014-BLG-0124, but it is only when they are combined with ~ 30 min of Keck II AO observations that the physical parameters of the host star are well measured.

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