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Results for "S. V. Jeffers"

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The effect of M dwarf starspot activity on low-mass planet detection thresholdsNov 04 2010In light of the growing interest in searching for low mass, rocky planets, we investigate the impact of starspots on radial velocity searches for earth-mass planets in orbit about M dwarf stars. Since new surveys targeting M dwarfs will likely be carried ... More
Magnetic activity on AB Doradus: Temporal evolution of starspots and differential rotation from 1988 to 1994Oct 09 2006Surface brightness maps for the young K0 dwarf AB Doradus are reconstructed from archival data sets for epochs spanning 1988 to 1994. By using the signal-to-noise enhancement technique of Least-Squares Deconvolution, our results show a greatly increased ... More
Variable magnetic field geometry of the young sun HN Peg (HD 206860)Oct 30 2014The large-scale magnetic field of solar-type stars reconstructed from their spectropolarimetric observations provide important insight into their underlying dynamo processes.We aim to investigate the temporal variability of the large-scale surface magnetic ... More
Hubble Space Telescope Observations of SV Cam: II. First Derivative Lightcurve Modelling using PHOENIX and ATLAS Model AtmospheresFeb 02 2006The variation of the specific intensity across the stellar disc is essential input parameter in surface brightness reconstruction techniques such as Doppler imaging, where the relative intensity contributions of different surface elements are important ... More
Direct Evidence for a Polar Spot on SV CamJan 31 2005We have used spectrophotometric data from the Hubble Space Telescope to eclipse-map the primary component of the RS CVn binary SV Cam over 9 HST orbits. We find from these observations and the HIPPARCOS parallax that the surface flux in the eclipsed low-latitude ... More
Fidelity for imperfect postselectionNov 26 2007We describe a simple measure of fidelity for mixed state postselecting devices. The measure is most appropriate for postselection where the task performed by the output is only effected by a specific state.
Constraining the Circumbinary Envelope of Z CMa via imaging polarimetryMay 16 2012Z CMa is a complex binary system, composed of a Herbig Be and an FU Ori star. The Herbig star is surrounded by a dust cocoon of variable geometry, and the whole system is surrounded by an infalling envelope. Previous spectropolarimetric observations have ... More
Hubble Space Telescope Observations of SV Cam: I. The Importance of Unresolved Starspot Distributions in Lightcurve FittingFeb 02 2006We have used maximum entropy eclipse mapping to recover images of the visual surface brightness distribution of the primary component of the RS CVn eclipsing binary SV Cam, using high-precision photometry data obtained during three primary eclipses with ... More
Data Reduction Techniques for High Contrast Imaging Polarimetry. Applications to ExPoMay 15 2011Imaging polarimetry is a powerful tool for detecting and characterizing exoplanets and circumstellar environments. Polarimetry allows a separation of the light coming from an unpolarized source such as a star and the polarized source such as a planet ... More
Imaging the circumstellar environment of the young T Tauri star SU AurigaeNov 19 2013The circumstellar environments of classical T Tauri stars are challenging to directly image because of their high star-to-disk contrast ratio. One method to overcome this is by using imaging polarimetry where scattered and consequently polarised starlight ... More
PolarBase: a data base of high resolution spectropolarimetric stellar observationsJan 06 2014Apr 22 2014PolarBase is an evolving data base that contains all stellar data collected with the ESPaDOnS and NARVAL high-resolution spectropolarimeters, in their reduced form, as soon as they become public. As of early 2014, observations of 2,000 stellar objects ... More
Substellar companions and isolated planetary mass objects from protostellar disc fragmentationOct 23 2003Self-gravitating protostellar discs are unstable to fragmentation if the gas can cool on a time scale that is short compared to the orbital period. We use a combination of hydrodynamic simulations and N-body orbit integrations to study the long term evolution ... More
Is it possible to detect planets around young active G and K dwarfs?Nov 14 2013Theoretical predictions suggest that the distribution of planets in very young stars could be very different to that typically observed in Gyr old systems that are the current focus of radial velocity surveys. However, the detection of planets around ... More
The Extreme Polarimeter: Design, Performance, First Results & UpgradesNov 27 2012Well over 700 exoplanets have been detected to date. Only a handful of these have been observed directly. Direct observation is extremely challenging due to the small separation and very large contrast involved. Imaging polarimetry offers a way to decrease ... More
The color dependent morphology of the post-AGB star HD161796Mar 07 2013Context. Many protoplanetary nebulae show strong asymmetries in their surrounding shell, pointing to asymmetries during the mass loss phase. Questions concerning the origin and the onset of deviations from spherical symmetry are important for our understanding ... More
Could a change in magnetic field geometry cause the break in the wind-activity relation?Sep 29 2015Wood et al suggested that mass-loss rate is a function of X-ray flux ($\dot{M} \propto F_x^{1.34}$) for dwarf stars with $F_x \lesssim F_{x,6} \equiv 10^6$ erg cm$^{-2}$ s$^{-1}$. However, more active stars do not obey this relation. These authors suggested ... More
Starspot distributions on fully convective M dwarfs: implications for radial velocity planet searchesSep 17 2015Since M4.5 - M9 dwarfs exhibit equatorial rotation velocities of order 10 km/s on average, radial velocity surveys targeting this stellar population will likely need to find methods to effectively remove starspot jitter. We present the first high resolution ... More
The relation between stellar magnetic field geometry and chromospheric activity cycles II: The rapid 120 day magnetic cycle of Tau BootisMay 24 2018One of the aims of the BCool programme is to search for cycles in other stars and to understand how similar they are to the Sun. In this paper we aim to monitor the evolution of $\tau$ Boo's large-scale magnetic field using high-cadence observations covering ... More
Recovering planet radial velocity signals in the presence of starspot activity in fully convective starsDec 03 2016Accounting for stellar activity is a crucial component of the search for ever-smaller planets orbiting stars of all spectral types. We use Doppler imaging methods to demonstrate that starspot induced radial velocity variability can be effectively reduced ... More
The evolution of surface magnetic fields in young solar-type stars I: the first 250 MyrJan 04 2016The surface rotation rates of young solar-type stars vary rapidly with age from the end of the pre-main sequence through the early main sequence. Important changes in the dynamos operating in these stars may result from this evolution, which should be ... More
Temporal variability of the wind from the star τ BoötisMar 30 2016We present new wind models for {\tau} Bo\"otis ({\tau} Boo), a hot-Jupiter-host-star whose observable magnetic cycles makes it a uniquely useful target for our goal of monitoring the temporal variability of stellar winds and their exoplanetary impacts. ... More
Surprisingly different starspot distributions on the near equal-mass equal-rotation-rate stars in the M dwarf binary GJ 65 ABJun 13 2017We aim to understand how stellar parameters such as mass and rotation impact the distribution of starspots on the stellar surface. To this purpose, we have used Doppler imaging to reconstruct the surface brightness distributions of three fully convective ... More
Chromospheric activity catalogue of 4454 cool stars. Questioning the active branch of stellar activity cyclesMar 29 2018Chromospheric activity monitoring of a wide range of cool stars can provide valuable information on stellar magnetic activity and its dependence on fundamental stellar parameters such as effective temperature and rotation.We compile a chromospheric activity ... More
Magnetism, chemical spots, and stratification in the HgMn star phi PhoenicisNov 25 2011Jan 27 2012Mercury-manganese (HgMn) stars have been considered as non-magnetic and non-variable chemically peculiar (CP) stars for a long time. However, recent discoveries of the variability in spectral line profiles have suggested an inhomogeneous surface distribution ... More
No magnetic field in the spotted HgMn star mu LeporisOct 04 2011Chemically peculiar stars of the mercury-manganese (HgMn) type represent a new class of spotted late-B stars, in which evolving surface chemical inhomogeneities are apparently unrelated to the presence of strong magnetic fields but are produced by some ... More
First detection of linear polarization in the line profiles of active cool starsMar 30 2011The application of high-resolution spectropolarimetry has led to major progress in understanding the magnetism and activity of late-type stars. During the last decade, magnetic fields have been discovered and mapped for many types of active cool stars ... More
Are there tangled magnetic fields on HgMn stars?Apr 24 2013Several recent spectrophotometric studies failed to detect significant global magnetic fields in late-B HgMn chemically peculiar stars, but some investigations have suggested the presence of strong unstructured or tangled fields in these objects. We used ... More
Three-dimensional magnetic and abundance mapping of the cool Ap star HD 24712 I. Spectropolarimetric observations in all four Stokes parametersJun 05 2013High-resolution spectropolarimetric observations provide simultaneous information about stellar magnetic field topologies and three-dimensional distributions of chemical elements. Here we present analysis of a unique full Stokes vector spectropolarimetric ... More
Magnetically Controlled Accretion on the Classical T Tauri Stars GQ Lupi and TW HydraeJan 14 2013Jan 29 2013We present high spectral resolution ($R\approx108,000$) Stokes $V$ polarimetry of the Classical T Tauri stars (CTTSs) GQ Lup and TW Hya obtained with the polarimetric upgrade to the HARPS spectrometer on the ESO 3.6 m telescope. We present data on both ... More
The search for magnetic fields in mercury-manganese starsOct 19 2010We performed a highly sensitive search for magnetic fields on a large set of HgMn stars. With the aid of a new polarimeter attached to the HARPS spectrometer at the ESO 3.6m-telescope, we obtained high-quality circular polarization spectra of 41 single ... More
A BCool survey of the magnetic fields of planet-hosting solar-type starsNov 23 2016We present a spectropolarimetric snapshot survey of solar-type planet hosting stars. In addition to 14 planet-hosting stars observed as part of the BCool magnetic snapshot survey, we obtained magnetic observations of a further 19 planet-hosting solar-type ... More
Chemical spots in the absence of magnetic field in the binary HgMn star 66 EridaniFeb 23 2011According to our current understanding, a subclass of the upper main sequence chemically peculiar stars, called mercury-manganese (HgMn), is non-magnetic. Nevertheless, chemical inhomogeneities were recently discovered on their surfaces. At the same time, ... More
Precision radial velocities of 15 M5 - M9 dwarfsJan 21 2014Jan 23 2014We present radial velocity measurements of a sample of M5V-M9V stars from our Red-Optical Planet Survey, ROPS, operating at 0.65-1.025 micron. Radial velocities for 15 stars, with r.m.s. precision down to 2.5 m/s over a week long time scale are achieved ... More
ROPS: A New Search for Habitable Earths in the Southern SkyApr 27 2012May 04 2012We present the first results from our Red Optical Planet Survey (ROPS) to search for low mass planets orbiting late type dwarfs (M5.5V - M9V) in their habitable zones (HZ). Our observations, with the red arm of the MIKE spectrograph (0.5 - 0.9 microns) ... More
The Solar Wind in Time II: 3D stellar wind structure and radio emissionNov 13 2018In this work, we simulate the evolution of the solar wind along its main sequence lifetime and compute its thermal radio emission. To study the evolution of the solar wind, we use a sample of solar mass stars at different ages. All these stars have observationally-reconstructed ... More
The Evolving Magnetic Topology of $τ$ BoötisApr 08 2016We present six epochs of spectropolarimetric observations of the hot-Jupiter-hosting star $\tau$ Bo\"otis that extend the exceptional previous multi-year data set of its large-scale magnetic field. Our results confirm that the large-scale magnetic field ... More
Surprising detection of an equatorial dust lane on the AGB star IRC+10216Dec 16 2014Understanding the formation of planetary nebulae remains elusive because in the preceding asymtotic giant branch (AGB) phase these stars are heavily enshrouded in an optically thick dusty envelope. To further understand the morphology of the circumstellar ... More
Direct imaging of a massive dust cloud around R Coronae BorealisMar 06 2012We present recent polarimetric images of the highly variable star R CrB using ExPo and archival WFPC2 images from the HST. We observed R CrB during its current dramatic minimum where it decreased more than 9 mag due to the formation of an obscuring dust ... More
BP Piscium: its flaring disk imaged with SPHERE/ZIMPOLOct 20 2016Whether BP Piscium (BP Psc) is either a pre-main sequence T Tauri star at d ~ 80 pc, or a post-main sequence G giant at d ~ 300 pc is still not clear. As a first-ascent giant, it is the first to be observed with a molecular and dust disk. Alternatively, ... More
Multiple views of magnetism in cool starsAug 16 2012Magnetic fields are regarded as a crucial element for our understanding of stellar physics. They can be studied with a variety of methods which provide complementary - and sometimes contradictory - information about the structure, strength and dynamics ... More
A solar-like magnetic cycle on the mature K-dwarf 61 Cyg A (HD 201091)Jun 03 2016The long-term monitoring of magnetic cycles in cool stars is a key diagnostic in understanding how dynamo generation and amplification of magnetic fields occur in stars similar in structure to the Sun. We investigate the temporal evolution of a possible ... More
Studying stellar spin-down with Zeeman-Doppler magnetogramsMay 04 2017Magnetic activity and rotation are known to be intimately linked for low-mass stars. Understanding rotation evolution over the stellar lifetime is therefore an important goal within stellar astrophysics. In recent years, there has been increased focus ... More
The energy budget of stellar magnetic fields: comparing non-potential simulations and observationsOct 26 2016The magnetic geometry of the surface magnetic fields of more than 55 cool stars have now been mapped using spectropolarimetry. In order to better understand these observations, we compare the magnetic field topology at different surface scale sizes of ... More
Spectroscopic characterisation of CARMENES target candidates from FEROS, CAFE and HRS high-resolution spectraJul 29 2016CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrographs) started a new planet survey on M-dwarfs in January this year. The new high-resolution spectrographs are operating in the visible ... More
CARMENES input catalogue of M dwarfs II. High-resolution imaging with FastCamAug 29 2016Aims: We search for low-mass companions of M dwarfs and characterize their multiplicity fraction with the purpose of helping in the selection of the most appropriate targets for the CARMENES exoplanet survey. Methods: We obtained high-resolution images ... More
J band Variability of M Dwarfs in the WFCAM Transit SurveyNov 22 2012Dec 07 2012We present an analysis of the photometric variability of M dwarfs in the WFCAM Transit Survey. Although periodic lightcurve variability in low mass stars is generally dominated by photospheric star spot activity, M dwarf variability in the J band has ... More
Magnetic field and wind of Kappa Ceti: towards the planetary habitability of the young Sun when life arose on EarthMar 12 2016We report magnetic field measurements for Kappa1~Cet, a proxy of the young Sun when life arose on Earth. We carry out an analysis of the magnetic properties determined from spectropolarimetric observations and reconstruct its large-scale surface magnetic ... More
Efficient scheduling of astronomical observations. Application to the CARMENES radial-velocity surveyJul 19 2017Jun 06 2018Targeted 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 ... More
Surface magnetism of cool starsDec 11 2016Magnetic fields are essential ingredients of many physical processes in the interiors and envelopes of cool stars. Yet their direct detection and characterisation is notoriously difficult, requiring high-quality observations and advanced analysis techniques. ... More
A maximum entropy approach to detect close-in giant planets around active starsFeb 28 2015Oct 09 2015(shortened for arXiv) We aim to progress towards more efficient exoplanet detection around active stars by optimizing the use of Doppler Imaging in radial velocity measurements. We propose a simple method to simultaneously extract a brightness map and ... More
CARMENES input catalogue of M dwarfs. I. Low-resolution spectroscopy with CAFOSFeb 26 2015Context. CARMENES is a stabilised, high-resolution, double-channel spectrograph at the 3.5 m Calar Alto telescope. It is optimally designed for radial-velocity surveys of M dwarfs with potentially habitable Earth-mass planets. Aims. We prepare a list ... More
Experimental Implementation of a Quantum Optical State Comparison AmplifierApr 16 2014Quantum optical amplification that beats the noise addition limit for deterministic amplifiers has been realized experimentally using several different nondeterministic protocols. These schemes either require single-photon sources, or operate by noise ... More
Experimental demonstration of quantum digital signatures using phase-encoded coherent states of lightJun 04 2013Digital signatures are frequently used in data transfer to prevent impersonation, repudiation and message tampering. Currently used classical digital signature schemes rely on public key encryption techniques, where the complexity of so-called "one-way" ... More
The CARMENES search for exoplanets around M dwarfs. Period search in H$α$, Na I D, and Ca II IRT linesJan 16 2019We use spectra from CARMENES, the Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs, to search for periods in chromospheric indices in 16 M0 to M2 dwarfs. We measure spectral indices in ... More
Magnetic fields in M dwarfs from the CARMENES surveyApr 29 2019M dwarfs are known to generate the strongest magnetic fields among main-sequence stars with convective envelopes, but the link between the magnetic fields and underlying dynamo mechanisms, rotation, and activity still lacks a consistent picture. In this ... More
The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectraMar 06 2018Previous 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 ... More
The CARMENES search for exoplanets around M dwarfs - Photospheric parameters of target stars from high-resolution spectroscopyFeb 08 2018The new CARMENES instrument comprises two high-resolution and high-stability spectrographs that are used to search for habitable planets around M dwarfs in the visible and near-infrared regime via the Doppler technique. Characterising our target sample ... More
CARMENES input catalogue of M dwarfs IV. New rotation periods from photometric time seriesOct 08 2018Aims. The main goal of this work is to measure rotation periods of the M-type dwarf stars being observed by the CARMENES exoplanet survey to help distinguish radial-velocity signals produced by magnetic activity from those produced by exoplanets. Rotation ... More
Modelling the Hidden Magnetic Field of Low-Mass StarsJan 18 2014Zeeman-Doppler imaging is a spectropolarimetric technique that is used to map the large-scale surface magnetic fields of stars. These maps in turn are used to study the structure of the stars' coronae and winds. This method, however, misses any small-scale ... More
Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicatorsOct 27 2017Context: 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 ... More
The connection between stellar activity cycles and magnetic field topologyOct 12 2016Zeeman Doppler imaging has successfully mapped the large-scale magnetic fields of stars over a large range of spectral types, rotation periods and ages. When observed over multiple epochs, some stars show polarity reversals in their global magnetic fields. ... More
The energy budget of stellar magnetic fieldsAug 06 2015Spectropolarimetric observations have been used to map stellar magnetic fields, many of which display strong bands of azimuthal fields that are toroidal. A number of explanations have been proposed to explain how such fields might be generated though ... More
The CARMENES search for exoplanets around M dwarfs. Activity indicators at visible and near-infrared wavelengthsJan 25 2019The CARMENES survey is searching for Earth-like planets orbiting M dwarfs using the radial velocity method. Studying the stellar activity of the target stars is important to avoid false planet detections and to improve our understanding of the atmospheres ... More
The CARMENES search for exoplanets around M dwarfs: Wing asymmetries of H$α$, Na I D, and He I linesJan 31 2018Stellar activity is ubiquitously encountered in M dwarfs and often characterised by the H$\alpha$ line. In the most active M dwarfs, H$\alpha$ is found in emission, sometimes with a complex line profile. Previous studies have reported extended wings and ... More
A Bcool magnetic snapshot survey of solar-type starsNov 14 2013Stellar magnetic field measurements obtained from spectropolarimetry offer key data for activity and dynamo studies, and we present the results of a major high-resolution spectropolarimetric Bcool project magnetic snapshot survey of 170 solar-type stars ... More
Analysis of combined radial velocities and activity of BD+20 1790: evidence supporting the existence of a planetary companionFeb 18 2015This paper presents the simultaneous Bayesian analysis of the radial velocity and activity indices for the K5Ve active star BD+20 1790, that was proposed to host a close-in massive planet by Hern\'an-Obispo et al. (2010). The Bayesian analysis supports ... More
The effects of stellar winds on the magnetospheres and potential habitability of exoplanetsSep 03 2014Context: The principle definition of habitability for exoplanets is whether they can sustain liquid water on their surfaces, i.e. that they orbit within the habitable zone. However, the planet's magnetosphere should also be considered, since without it, ... More
Radial velocity signatures of Zeeman broadeningJan 14 2013Stellar activity signatures such as spots and plage can significantly limit the search for extrasolar planets. Current models of activity-induced radial velocity (RV) signals focused on the impact of temperature contrast in spots predicting the signal ... More
CARMENES input catalogue of M dwarfs: III. Rotation and activity from high-resolution spectroscopic observationsFeb 06 2018CARMENES 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 ... More
Security against jamming and noise exclusion in imagingSep 09 2016We describe a protocol by which an imaging system could be protected against jamming by a malevolent party. Our protocol not only allows recognition of the jamming, but also allows for the recovery of the true image from the jammed one. We apply the method ... More
No evidence for activity correlations in the radial velocities of Kapteyn's starJun 30 2015Stellar activity may induce Doppler variability at the level of a few m/s which can then be confused by the Doppler signal of an exoplanet orbiting the star. To first order, linear correlations between radial velocity measurements and activity indices ... More
Realization of Quantum Digital Signatures without the requirement of quantum memoryNov 22 2013May 14 2014Digital signatures are widely used to provide security for electronic communications, for example in financial transactions and electronic mail. Currently used classical digital signature schemes, however, only offer security relying on unproven computational ... More
The CARMENES search for exoplanets around M dwarfs. Chromospheric modeling of M2-3 V stars with PHOENIXFeb 11 2019Chromospheric modeling of observed differences in stellar activity lines is imperative to fully understand the upper atmospheres of late-type stars. We present one-dimensional parametrized chromosphere models computed with the atmosphere code PHOENIX ... More
The CARMENES search for exoplanets around M dwarfs: Nine new double-line spectroscopic binary starsAug 21 2018Context. 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 ... More
Two planets around Kapteyn's star : a cold and a temperate super-Earth orbiting the nearest halo red-dwarfJun 03 2014Exoplanets of a few Earth masses can be now detected around nearby low-mass stars using Doppler spectroscopy. In this paper, we investigate the radial velocity variations of Kapteyn's star, which is both a sub-dwarf M-star and the nearest halo object ... More
The CARMENES search for exoplanets around M dwarfs - The enigmatic planetary system GJ 4276: One eccentric planet or two planets in a 2:1 resonance?Jan 07 2019We report the detection of a Neptune-mass exoplanet around the M4.0 dwarf GJ 4276 (G 232-070) based on radial velocity (RV) observations obtained with the CARMENES spectrograph. The RV variations of GJ 4276 are best explained by the presence of a planetary ... More
The CARMENES search for exoplanets around M dwarfs: Different roads to radii and masses of the target starsApr 05 2019We determine the radii and masses of 293 nearby, bright M dwarfs of the CARMENES survey. This is the first time that such a large and homogeneous high-resolution (R>80 000) spectroscopic survey has been used to derive these fundamental stellar parameters. ... More
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)Oct 17 2018We 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 ... More
Quantum nature of laser lightSep 15 2005All compositions of a mixed-state density operator are equivalent for the prediction of the probabilities of future outcomes of measurements. For retrodiction, however, this is not the case. The retrodictive formalism of quantum mechanics provides a criterion ... More
The CARMENES search for exoplanets around M dwarfs. A Neptune-mass planet traversing the habitable zone around HD 180617Aug 03 2018Despite 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, ... More
High-resolution spectropolarimetric of k Cet: A proxy for the young SunOct 28 2013Among the solar proxies studied in the Sun in Time k Cet (HD 20630) stands out as potentially having a mass very close to solar and a young age. On this study, we monitored the magnetic field and the chromospheric activity from the Ca II H & K lines of ... More
A terrestrial planet candidate in a temperate orbit around Proxima CentauriSep 12 2016At a distance of 1.295 parsecs, the red-dwarf Proxima Centauri ($\alpha$ Centauri C, GL 551, HIP 70890, or simply Proxima) is the Sun's closest stellar neighbor and one of the best studied low-mass stars. It has an effective temperature of only $\sim$ ... More
The CARMENES search for exoplanets around M dwarfs Detection of a mini-Neptune around LSPM J2116+0234 and refinement of orbital parameters of a super-Earth around GJ 686 (BD+18 3421)May 22 2019Although M dwarfs are known for high levels of stellar activity, they are ideal targets for the search of low-mass exoplanets with the radial velocity (RV) method. We report the discovery of a planetary-mass companion around LSPM J2116+0234 (M3.0 V) and ... More
The Quantum Hilbert HotelJun 01 2015In 1924 David Hilbert conceived a paradoxical tale involving a hotel with an infinite number of rooms to illustrate some aspects of the mathematical notion of "infinity". In continuous-variable quantum mechanics we routinely make use of infinite state ... More
Quantum Optical State Comparison AmplifierNov 22 2013It is a fundamental principle of quantum theory that an unknown state cannot be copied or, as a consequence, an unknown optical signal cannot be amplified deterministically and perfectly. Here we describe a protocol that provides nondeterministic quantum ... More
Detection of He I $\lambda10830$ Å absorption on HD 189733 b with CARMENES high-resolution transmission spectroscopyDec 06 2018We 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 \AA{} in all three transits. During mid-transit, ... More
Gliese 49: Activity evolution and detection of a super-EarthMar 12 2019Mar 25 2019Small planets around low-mass stars often show orbital periods in a range that corresponds to the temperate zones of their host stars which are therefore of prime interest for planet searches. Surface phenomena such as spots and faculae create periodic ... More
Gliese 49: Activity evolution and detection of a super-EarthMar 12 2019Small planets around low-mass stars often show orbital periods in a range that corresponds to the temperate zones of their host stars which are therefore of prime interest for planet searches. Surface phenomena such as spots and faculae create periodic ... More
Frictional quantum decoherenceJul 19 2007The dynamics associated with a measurement-based master equation for quantum Brownian motion are investigated. A scheme for obtaining time evolution from general initial conditions is derived. This is applied to analyze dissipation and decoherence in ... More
The Rotationally Modulated Polarization of $ξ$ Boo ANov 21 2018Feb 10 2019We have observed the active star $\xi$ Boo A (HD 131156A) with high precision broadband linear polarimetry contemporaneously with circular spectropolarimetry. We find both signals are modulated by the 6.43 day rotation period of $\xi$ Boo A. The signals ... More
Stellar activity analysis of Barnard's Star: Very slow rotation and evidence for long-term activity cycleDec 17 2018The search for Earth-like planets around late-type stars using ultra-stable spectrographs requires a very precise characterization of the stellar activity and the magnetic cycle of the star, since these phenomena induce radial velocity (RV) signals that ... More
The Type II-Plateau Supernova 2017eaw in NGC 6946 and Its Red Supergiant ProgenitorMar 09 2019We present extensive optical photometric and spectroscopic observations, from 4 to 482 days after explosion, of the Type II-plateau (II-P) supernova (SN) 2017eaw in NGC 6946. SN 2017eaw is a normal SN II-P intermediate in properties between, for example, ... More
The Type II-Plateau Supernova 2017eaw in NGC 6946 and Its Red Supergiant ProgenitorMar 09 2019Apr 18 2019We present extensive optical photometric and spectroscopic observations, from 4 to 482 days after explosion, of the Type II-plateau (II-P) supernova (SN) 2017eaw in NGC 6946. SN 2017eaw is a normal SN II-P intermediate in properties between, for example, ... More
Stellar magnetism: empirical trends with age and rotationApr 10 2014We investigate how the observed large-scale surface magnetic fields of low-mass stars (~0.1 -- 2 Msun), reconstructed through Zeeman-Doppler imaging (ZDI), vary with age t, rotation and X-ray emission. Our sample consists of 104 magnetic maps of 73 stars, ... More
A candidate super-Earth planet orbiting near the snow line of Barnard's starNov 14 2018Nov 23 2018At 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 ... More
Atomic RetrodictionJul 04 2001Measurement of a quantum system provides information concerning the state in which it was prepared. In this paper we show how the retrodictive formalism can be used to evaluate the probability associated with any one of a given set of preparation events. ... More
Measuring NothingJul 12 2012Measurement is integral to quantum information processing and communication; it is how information encoded in the state of a system is transformed into classical signals for further use. In quantum optics, measurements are typically destructive, so that ... More
Retrodiction with two-level atoms: atomic previvalsJul 30 2002In the Jaynes-Cummings model a two-level atom interacts with a single-mode electromagnetic field. Quantum mechanics predicts collapses and revivals in the probability that a measurement will show the atom to be excited at various times after the initial ... More
Quantum theory of preparation and measurementJul 30 2002The conventional postulate for the probabilistic interpretation of quantum mechanics is asymmetric in preparation and measurement, making retrodiction reliant on inference by use of Bayes' theorem. Here, a more fundamental symmetric postulate is presented, ... More
Master Equation for Retrodiction of Quantum Communication SignalsJul 27 2001We derive the master equation that governs the evolution of the measured state backwards in time in an open system. This allows us to determine probabilities for a given set of preparation events from the results of subsequent measurements, which has ... More