Ultrashort-period (USP) exoplanets have orbital periods shorter than 1 day. Precise masses and radii of USP exoplanets could provide constraints on their unknown formation and evolution processes. We ...report the detection and characterization of the USP planet GJ 367b using high-precision photometry and radial velocity observations. GJ 367b orbits a bright (
-band magnitude of 10.2), nearby, and red (M-type) dwarf star every 7.7 hours. GJ 367b has a radius of 0.718 ± 0.054 Earth-radii and a mass of 0.546 ± 0.078 Earth-masses, making it a sub-Earth planet. The corresponding bulk density is 8.106 ± 2.165 grams per cubic centimeter—close to that of iron. An interior structure model predicts that the planet has an iron core radius fraction of 86 ± 5%, similar to that of Mercury’s interior.
We present the discovery from Transiting Exoplanet Survey Satellite (TESS) data of LTT 1445Ab. At a distance of 6.9 pc, it is the second nearest transiting exoplanet system found to date, and the ...closest one known for which the primary is an M dwarf. The host stellar system consists of three mid-to-late M dwarfs in a hierarchical configuration, which are blended in one TESS pixel. We use MEarth data and results from the Science Processing Operations Center data validation report to determine that the planet transits the primary star in the system. The planet has a radius of {1.38}_{-0.12}^{+0.13} {R}_{\oplus }, an orbital period of {5.35882}_{-0.00031}^{+0.00030} days, and an equilibrium temperature of {433}_{-27}^{+28} K. With radial velocities from the High Accuracy Radial Velocity Planet Searcher, we place a 3σ upper mass limit of 8.4 {M}_{\oplus } on the planet. LTT 1445Ab provides one of the best opportunities to date for the spectroscopic study of the atmosphere of a terrestrial world. We also present a detailed characterization of the host stellar system. We use high-resolution spectroscopy and imaging to rule out the presence of any other close stellar or brown dwarf companions. Nineteen years of photometric monitoring of A and BC indicate a moderate amount of variability, in agreement with that observed in the TESS light-curve data. We derive a preliminary astrometric orbit for the BC pair that reveals an edge-on and eccentric configuration. The presence of a transiting planet in this system hints that the entire system may be co-planar, implying that the system may have formed from the early fragmentation of an individual protostellar core.
Depuis la première détection d'une planète extrasolaire autour d'une étoile de type solaire par Mayor et Queloz (1995), plus de 1500 planètes ont été découverts. Actuellement il existe un énorme ...intérêt à découvrir et caractériser des planètes semblables à la Terre, en particulier celles situées dans la zone habitable de leur étoile hôte (définie comme la distance à l'étoile hôte où la température de la planète permet l'existence d'eau liquide à la surface). La détection de planètes de type terrestre, et la recherche de biomarqueurs dans leurs atmosphères sont parmi les principaux objectifs de l'astronomie du vingt et unième siècle. La méthode des vitesses radiales (VR), consistant à mesurer le mouvement réflexe de l'étoile induit par des planètes en orbite, est une remarquable technique pour atteindre cet objectif.Pour atteindre les précisions nécessaire à la detection de telles planètes il est absolument nécessaire de concevoir des spectrographes extrêmement stables, d'avoir une très bonne compréhension de l'activité stellaire (qui peut mimer l'effet d'une planète), d'effectuer un traitement soigneux de l'atmosphère terrestre (laquelle inévitablement laisse des empreintes dans les spectres acquis depuis le sol), et de disposer d'une puissante technique pour extraire, à partir des spectres, autant d'information Doppler que possible. La recherche de planètes orbitant autour des étoiles de très faible masse, plutôt qu'autour des étoiles de type solaire, permet d'aborder dès maintenant la détection de planètes de faible masse dans la zone habitable. En effet, en gardant tout les autres paramètres égaux, le mouvement réflexe (et donc l'amplitude de la variation VR) sera plus grande si l'étoile centrale est de très faible masse. De plus les naines M ont une plus faible luminosité que les étoiles de type solaire, il en resulte des périodes orbitales courtes des planètes dans la zone habitable (~50 jours pour les naines M contre ~360 jours pour des étoiles de type solaire), entraînant à nouveau en une plus grande amplitude des VR. Une précision de ~1 m/s en VR permet la détection d'une planète dans la zone habitable d'une naine M, alors que ~0.1 m/s sont nécessaire dans le cas d'une étoile de type solaire.Cette thèse vise à optimiser l'extraction de VR des spectres des naines M à haute résolution acquis avec le spectrographe HARPS (avec une possibilité d'applications futures sur d'autres instruments comme SOPHIE, HARPS-N et le prochain spectrographe infrarouge SPIRou - prochainement mis en service au CFHT). Les effets de l'activité stellaire des naines M seront également analysées, dans le contexte de la technique des VR. Divers traceurs d'activité stellaire sont utilisés pour rejeter des fausses détections ou pour étudier les relations entre l'activité magnétique et la rotation. Dans cette thèse (Chap. 3) je calibre pour la première fois le flux dans les raies H et K du Calcium en fonction de la luminosité bolométrique et je détermine la relation entre cet estimateur R'HK et la période de rotation des naines M. Dans le chapitre 4 je décris l'implémentation d'une méthode d'extraction de VR par une minimisation du Chi-deux entre un template spectral et les spectres observés. Je démontre que cette méthode est plus précise que celle classiquement utilisée. Les raies telluriques qui affectent les mesures VR sont prises en compte dans les procédures d'analyse. Ces méthodes sont testées sur des systèmes avec des candidats planétaires, je discuterais l'analyse de certains de ces systèmes.
Since the first detection of an extrasolar planet orbiting a Sun-like star by Mayor and Queloz (1995), more than 1500 have been discovered. Enormous interest is currently focused on finding and characterising Earth-like planets, in particular those located in the habitable zone of their host star (defined as the distance from the host star where the planet temperature allows liquid water to flow on its surface). Both the detection of Earth-like planets, and the search for biomarkers in their atmospheres are among the main objectives of the twenty-first century's astronomy. The method known as radial velocities (RV), that consists in the measure of the star's reflex motion induced by orbiting planets, is a promising technique to achieve that quest.The main difficulties with the RV technique are the needs of an extremely stable spectrograph, a correct understanding of stellar activity (which can mimic the effect of a planet), a careful treatment of our Earth's atmosphere (which inevitable imprints spectra taken from the ground), and the need to dispose of a powerful algorithm to extract as much Doppler information as possible from the recorded spectra. Search for planets orbiting very low-mass stars (M dwarfs) can more easily reach the goal of detecting low-mass planets in the habitable zone of their parent star, compared to solar-type stars. Indeed, everything else being equal, a lower mass of the host star implies a larger reflex motion, and thus a larger RV amplitude. Moreover, the lower luminosity of M dwarfs compared to Sun-like stars, implies shorter orbital periods from planets in the habitable zone (~50 days against ~360 days, for M dwarfs compared to solar-type stars, respectively), resulting again in a larger RV amplitude. A RV precision of ~1 m/s allows a planet detection in the habitable zone of an M dwarf, whereas ~0.1 m/s is required in the case of a solar-type stars.This thesis aims to optimise the RV extraction from HARPS high-resolution spectra (and to open similar analysis on other instruments like SOPHIE, HARPS-N and the upcoming infrared spectrograph SPIRou -- to be commissioned to the 3.6-m CFH-Telescope). The effects of stellar activity will also be analysed, and contextualised in the RV technique. Stellar activity tracers are used to reject false detections or to study the relationships between the stellar magnetic activity and rotation. In this thesis (Chap.ref{chap:mag_activity}) I calibrate for the first time the ratio between the Ca textrm{small II} Htextrm{small &}K chromospheric lines and the bolometric luminosity for M dwarfs. I determine a relationship between the R^prime_{HK}-index and the rotation period of M dwarfs. In chapter~ref{chap:template_matching} I describe my algorithm to extract RVs through a chi^2-minimisation between a stellar template and the observed spectra. I demonstrate the improved accuracy of this method. Telluric spectral lines also affect the measurements of RV and are taken into account in the analysis procedures. I tested these methods on systems with planetary candidates, and for some systems, I took in charge the Keplerian analysis.
Tesis para optar al grado de Magíster en Ciencias mención Astronomía
Este trabajo de investigaci on se enmarca en el t opico de planetas extrasolares y la caracterizaci on de sus;
atm osferas. A la ...fecha, m as de 600 exoplanetas han sido descubiertos mediante distintas t ecnicas, siendo;
la de los tr ansitos la de mayor inter es para el prop osito de esta investigaci on.;
Durante el tr ansito de un exoplaneta frente a su estrella, en la luz que recibimos del sistema existir an;
l neas espectrales debidas a la presencia de una atm osfera opticamente delgada que es atravesada por los;
fotones provenientes de la estrella. Para el estudio elegimos el sistema HD209458, donde el tipo espectral;
de la estrella es G0V (V=7.65) y el exoplaneta es un hot-Jupiter al que se le ha detectado atm osfera;
(Charbonneau et al., 2002; Vidal-Madjar et al., 2003, 2004; Lecavelier Des Etangs et al., 2008; D esert;
et al., 2008; Schlawin et al., 2010; Beaulieu et al., 2010). Este objeto es, hasta ahora, el m as analizado;
por ser el que mejor oportunidades entrega, en cuanto a contraste, para el an alisis de su atm osfera. El;
objetivo de esta tesis es detectar, identi car y caracterizar l neas espectrales debidas a la atm osfera del;
exoplaneta usando datos tomados con telescopios terrestres.;
La investigaci on se llev o a cabo con datos del archivo p ublico de VLT+UVES (ESO) y Subaru+HDS;
(NAOJ). Para poder encontrar l neas espectrales que se deban a la atm osfera de un exoplaneta se us o es-;
pectroscopia de transmisi on. Sin embargo, al tratarse de datos adquiridos mediante telescopios terrestres,;
existen ciertas l neas producidas por la atm osfera de la Tierra que para este prop osito contaminan el;
espectro de transmisi on. Por tanto, el m etodo a seguir tiene que ser capaz de identi car cu ales son las;
l neas tel uricas, para as poder removerlas de cada espectro y no confundirlas con nuestras l neas espectrales;
de inter es principal. Por ultimo, un an alisis bootstrap se utiliza para dar un respaldo estad stico a;
posibles detecciones.;
La importancia de este trabajo radica en que usando bases de datos con informaci on de las transiciones;
presentes en un determinado rango espectral, se automatiza el rastreo de l neas espectrales;
en busca de las evidencias que dejan las atmosferas de exoplanetas, especialmente en un ambiente tan;
din amico como lo es este area de la Astronom a. Adem as, es de gran relevancia la aplicaci on de nuevas;
t ecnicas para manejar correctamente los efectos que produce nuestra la atm ósfera de la Tierra en el caso;
de datos tomados con telescopios terrestres.
2021 ApJ 922 30 We present the discovery of 32 new double periodic variables (DPVs) located
toward the Galactic bulge. We found these objects among the nearly half a
million binary stars published by ...the Optical Gravitational Lensing Experiment
project. With this discovery, we increase the number of known DPVs in the Milky
Way by a factor of 2. The new set of DPVs contains 31 eclipsing binaries and
one ellipsoidal variable star. The orbital periods cover the range from 1.6 to
26 days, while long periods are detected between 47 and 1144 days. Our analysis
confirms a known correlation between orbital and long periods that is also
observed in similar systems in the Magellanic Clouds.
We present an intensive effort to refine the mass and orbit of the enveloped terrestrial planet GJ 1214 b using 165 radial velocity (RV) measurements taken with the HARPS spectrograph over a period ...of ten years. We conduct a joint analysis of the RVs with archival Spitzer/IRAC transits and measure a planetary mass and radius of \(8.17\pm 0.43 M_{\oplus}\) and \(2.742^{+0.050}_{-0.053} R_{\oplus}\). Assuming GJ 1214 b is an Earth-like core surrounded by a H/He envelope, we measure an envelope mass fraction of \(X_{\rm env}= 5.24^{+0.30}_{-0.29}\)%. GJ 1214 b remains a prime target for secondary eclipse observations of an enveloped terrestrial, the scheduling of which benefits from our tight constraint on the orbital eccentricity of \(<0.063\) at 95% confidence, which narrows the secondary eclipse window to 2.8 hours. By combining GJ 1214 with other mid-M dwarf transiting systems with intensive RV follow-up, we calculate the frequency of mid-M dwarf planetary systems with multiple small planets and find that \(90^{+5}_{-21}\)% of mid-M dwarfs with a known planet with mass \(\in 1,10 M_{\oplus}\) and orbital period \(\in 0.5,50\) days, will host at least one additional planet. We rule out additional planets around GJ 1214 down to \(3 M_{\oplus}\) within 10 days such that GJ 1214 is a single-planet system within these limits, a result that has a \(44^{+9}_{-5}\)% probability given the prevalence of multi-planet systems around mid-M dwarfs. We also investigate mid-M dwarf RV systems and show that the probability that all reported RV planet candidates are real planets is \(<12\)% at 99% confidence, although this statistical argument is unable to identify the probable false positives.
The nearby LHS 1678 (TOI-696) system contains two confirmed planets and a wide-orbit, likely-brown-dwarf companion, which orbit an M2 dwarf with a unique evolutionary history. The host star occupies ...a narrow "gap" in the HR diagram lower main sequence, associated with the M dwarf fully convective boundary and long-term luminosity fluctuations. This system is one of only about a dozen M dwarf multi-planet systems to date that hosts an ultra-short period planet (USP). Here we validate and characterize a third planet in the LHS 1678 system using TESS Cycle 1 and 3 data and a new ensemble of ground-based light curves. LHS 1678 d is a 0.98 +/-0.07 Earth radii planet in a 4.97-day orbit, with an insolation flux of 9.1 +0.9/-0.8 Earth insolations. These properties place it near 4:3 mean motion resonance with LHS 1678 c and in company with LHS 1678 c in the Venus zone. LHS 1678 c and d are also twins in size and predicted mass, making them a powerful duo for comparative exoplanet studies. LHS 1678 d joins its siblings as another compelling candidate for atmospheric measurements with the JWST and mass measurements using high-precision radial velocity techniques. Additionally, USP LHS 1678 b breaks the "peas-in-a-pod" trend in this system, although additional planets could fill in the "pod" beyond its orbit. LHS 1678's unique combination of system properties and their relative rarity among the ubiquity of compact multi-planet systems around M dwarfs makes the system a valuable benchmark for testing theories of planet formation and evolution.
We present a new algorithm for precision radial velocity (pRV) measurements, a line-by-line (LBL) approach designed to handle outlying spectral information in a simple but efficient manner. The ...effectiveness of the LBL method is demonstrated on two datasets, one obtained with SPIRou on Barnard's star, and the other with HARPS on Proxima Centauri. In the near-infrared, the LBL provides a framework for m/s-level accuracy in pRV measurements despite the challenges associated with telluric absorption and sky emission lines. We confirm with SPIRou measurements spanning 2.7 years that the candidate super-Earth on a 233-day orbit around Barnard's star is an artifact due to a combination of time-sampling and activity. The LBL analysis of the Proxima Centauri HARPS post-upgrade data alone easily recovers the Proxima b signal and also provides a 2-sigma detection of the recently confirmed 5-day Proxima d planet, but argues against the presence of the candidate Proxima c with a period of 1900 days. We provide evidence that the Proxima c signal is associated with small, unaccounted systematic effects affecting the HARPS-TERRA template matching RV extraction method for long-period signals. Finally, the LBL framework provides a very effective activity indicator, akin to the full width at half maximum derived from the cross-correlation function, from which we infer a rotation period of \(92.1^{+4.2}_{-3.5}\) days for Proxima.
KELT-11b is an inflated sub-Saturn with a hot atmosphere and that orbits a bright evolved subgiant star, making it a prime choice for atmospheric characterization, but that transits its host star for ...more than seven hours. We observed this system in series of three consecutive nights with the HARPS spectrograph and report on the analysis of the transmission spectrum obtained from this dataset. Our results highlight the potential for independent observations of a long-transiting planet over consecutive nights. Our study reveals a sodium excess absorption of \(0.28 \pm 0.05 \%\) and \(0.50 \pm 0.06 \%\) in the Na D1 and D2 lines, respectively. This corresponds to 1.44 and 1.69 times the white-light planet radius in the line cores. Wind pattern modeling tends to prefer day-to-night side winds with no vertical winds, which is surprising considering the planet bloatedness. The modeling of the Rossiter-Mclaughlin effect yields a significantly misaligned orbit, with a projected spin-orbit angle of \({\lambda} = -77.86^{+2.36}_{-2.26}{}^\circ\). The characteristics of KELT-11 b, notably its extreme scale height and long transit, make it an ideal and unique target for next-generation telescopes. Our results as well as recent findings from HST, TESS, and CHEOPS observations could make KELT-11 b a benchmark exoplanet in atmospheric characterization.
The radius valley carries implications for how the atmospheres of small planets form and evolve, but this feature is visible only with highly precise characterizations of many small planets. We ...present the characterization of nine planets and one planet candidate with both NASA TESS and ESA CHEOPS observations, which adds to the overall population of planets bordering the radius valley. While four of our planets - TOI 118 b, TOI 455 b, TOI 560 b, and TOI 562 b - have already been published, we vet and validate transit signals as planetary using follow-up observations for five new TESS planets, including TOI 198 b, TOI 244 b, TOI 262 b, TOI 444 b, and TOI 470 b. While a three times increase in primary mirror size should mean that one CHEOPS transit yields an equivalent model uncertainty in transit depth as about nine TESS transits in the case that the star is equally as bright in both bands, we find that our CHEOPS transits typically yield uncertainties equivalent to between two and 12 TESS transits, averaging 5.9 equivalent transits. Therefore, we find that while our fits to CHEOPS transits provide overall lower uncertainties on transit depth and better precision relative to fits to TESS transits, our uncertainties for these fits do not always match expected predictions given photon-limited noise. We find no correlations between number of equivalent transits and any physical parameters, indicating that this behavior is not strictly systematic, but rather might be due to other factors such as in-transit gaps during CHEOPS visits or nonhomogeneous detrending of CHEOPS light curves.
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