arXiv subjects

Tsevi Mazeh

Publications and source records attributed to Tsevi Mazeh.

At least 91 records · Page 5Linked to original sources

arXiv2015

Seventy new non-eclipsing BEER binaries discovered in CoRoT lightcurves and confirmed by RVs from AAOmega

We applied the BEER algorithm to the CoRoT lightcurves from the first five LRc fields and identified $481$ non-eclipsing BEER candidates with periodic lightcurve modulations and amplitudes of $0.5-87$ mmag. Medium-resolution spectra of $281$ candidates were obtained in a seven-night AAOmega radial-velocity (RV) campaign, with a precision of $\sim1$ km/s. The RVs confirmed the binarity of $70$ of the BEER candidates, with periods of $0.3-10$ days.

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arXiv2015

Photometric Amplitude Distribution of Stellar Rotation of Kepler KOIs-Indication for Spin-Orbit Alignment of Cool Stars and High Obliquity for Hot Stars

The observed amplitude of the rotational photometric modulation of a star with spots should depend on the inclination of its rotational axis relative to our line of sight. Therefore, the distribution of observed rotational amplitudes of a large sample of stars depends on the distribution of their projected axes of rotation. Thus, comparison of the stellar rotational amplitudes of the Kepler KOIs with those of Kepler single stars can provide a measure to indirectly infer the properties of the spin-orbit obliquity of Kepler planets. We apply this technique to the large samples of 993 KOIs and 33,614 single Kepler stars in temperature range of 3500-6500 K. We find with high significance that the amplitudes of cool KOIs are larger, on the order of 10%, than those of the single stars. In contrast, the amplitudes of hot KOIs are systematically lower. After correcting for an observational bias, we estimate that the amplitudes of the hot KOIs are smaller than the single stars by about the same factor of 10%. The border line between the relatively larger and smaller amplitudes, relative to the amplitudes of the single stars, occurs at about 6000K. Our results suggest that the cool stars have their planets aligned with their stellar rotation, while the planets around hot stars have large obliquities, consistent with the findings of Winn et al. (2010) and Albrecht et al. (2012). We show that the low obliquity of the planets around cool stars extends up to at least 50 days, a feature that is not expected in the framework of a model that assumes the low obliquity is due to planet-star tidal realignment.

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arXiv2015

Time variation of Kepler transits induced by stellar rotating spots - a way to distinguish between prograde and retrograde motion I. Theory

Some transiting planets discovered by the Kepler mission display transit timing variations (TTVs) induced by stellar spots that rotate on the visible hemisphere of their parent stars. An induced TTV can be observed when a planet crosses a spot and modifies the shape of the transit light curve, even if the time resolution of the data does not allow to detect the crossing event itself. We present an approach that can, in some cases, use the derived TTVs of a planet to distinguish between a prograde and a retrograde planetary motion with respect to the stellar rotation. Assuming a single spot darker than the stellar disc, spot crossing by the planet can induce measured positive (negative) TTV, if the crossing occurs in the first (second) half of the transit. On the other hand, the motion of the spot towards (away from) the center of the stellar visible disc causes the stellar brightness to decrease (increase). Therefore, for a planet with prograde motion, the induced TTV is positive when the local slope of the stellar flux at the time of transit is negative, and vice versa. Thus, we can expect to observe a negative (positive) correlation between the TTVs and the photometric slopes for prograde (retrograde) motion. Using a simplistic analytical approximation, and also the publicly available SOAP-T tool to produce light curves of transits with spot-crossing events, we show for some cases how the induced TTVs depend on the local stellar photometric slopes at the transit timings. Detecting this correlation in Kepler transiting systems with high enough signal-to-noise ratio can allow us to distinguish between prograde and retrograde planetary motions. In coming papers we present analyses of the KOIs and Kepler eclipsing binaries, following the formalism developed here.

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arXiv2015

BEER analysis of Kepler and CoRoT light curves: II. Evidence for superrotation in the phase curves of three Kepler hot Jupiters

We analyzed the Kepler light curves of four transiting hot Jupiter systems --- KOI-13, HAT-P-7, TrES-2, and Kepler-76, which show BEaming, Ellipsoidal and Reflection (BEER) phase modulations. The mass of the four planets can be estimated from either the beaming or the ellipsoidal amplitude, given the mass and radius of their parent stars. For KOI-13, HAT-P-7, and Kepler-76 we find that the beaming-based planetary mass estimate is larger than the mass estimated from the ellipsoidal amplitude, consistent with previous studies. This apparent discrepancy may be explained by equatorial superrotation of the planet atmosphere, which induces an angle shift of the planet reflection/emission phase modulation, as was suggested for Kepler-76 in the first paper of this series. We propose a modified BEER model that supports superrotation, assuming either a Lambertian or geometric reflection/emission phase function, and provides a photometry-consistent estimate of the planetary mass. Our analysis shows that for Kepler-76 and HAT-P-7, the Lambertian superrotation BEER model is highly preferable over an unshifted null model, while for KOI-13 it is preferable only at a 1.4 sigma level. For TrES-2 we do not find such preference. For all four systems the Lambertian superrotation model mass estimates are in excellent agreement with the planetary masses derived from, or constrained by, radial velocity measurements. This makes the Lambertian superrotation BEER model a viable tool for estimating the masses of hot Jupiters from photometry alone. We conclude that hot Jupiter superrotation may be a common phenomenon that can be detected in the visual light curves of Kepler.

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arXiv2014

Kepler and the seven dwarfs: detection of low-level day-timescale periodic photometric variations in white dwarfs

We make use of the high photometric precision of Kepler to search for periodic modulations among 14 normal (DA- and DB-type, likely non-magnetic) hot white dwarfs (WDs). In five, and possibly up to seven of the WDs, we detect periodic, ~2 hr to 10 d, variations, with semi-amplitudes of 60 - 2000 ppm, lower than ever seen in WDs. We consider various explanations: WD rotation combined with magnetic cool spots; rotation combined with magnetic dichroism; rotation combined with hot spots from an interstellar-medium accretion flow; transits by size ~50 - 200 km objects; relativistic beaming due to reflex motion caused by a cool companion WD; or reflection/re-radiation of the primary WD light by a brown-dwarf or giant-planet companion, undergoing illumination phases as it orbits the WD. Each mechanism could be behind some of the variable WDs, but could not be responsible for all five to seven variable cases. Alternatively, the periodicity may arise from UV metal-line opacity, associated with accretion of rocky material, a phenomenon seen in ~50% of hot WDs. Non-uniform UV opacity, combined with WD rotation and fluorescent optical re-emission of the absorbed UV energy, could perhaps explain our findings. Even if reflection by a planet is the cause in only a few of the seven cases, it would imply that hot Jupiters are very common around WDs. If some of the rotation-related mechanisms are at work, then normal WDs rotate as slowly as do peculiar WDs, the only kind for which precise rotation measurements have been possible to date. Followup observations for this sample, and the larger numbers of additional WDs now being monitored as part of the K2 Kepler mission extension, will soon discriminate among these possibilities.

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arXiv2014

KIC 9632895 - The 10th Kepler Transiting Circumbinary Planet

We present the discovery of KIC 9632895b, a 6.2 Earth-radius planet in a low-eccentricity, 240.5-day orbit about an eclipsing binary. The binary itself consists of a 0.93 and 0.194 solar mass pair of stars with an orbital period of 27.3 days. The plane of the planet's orbit is rapidly precessing, and its inclination only becomes sufficiently aligned with the primary star in the latter portion of the Kepler data. Thus three transits are present in the latter half of the light curve, but none of the three conjunctions that occurred during the first half of the light curve produced transits. The precession period is ~103 years, and during that cycle, transits are visible only ~8% of the time. This has the important implication that for every system like KIC 9632895 that we detect, there are ~12 circumbinary systems that exist but are not currently exhibiting transits. The planet's mass is too small to noticeably perturb the binary, consequently its mass is not measurable with these data; but our photodynamical model places a 1-sigma upper limit of 16 Earth masses. With a period 8.8 times that of the binary, the planet is well outside the dynamical instability zone. It does, however, lie within the habitable zone of the binary, and making it the third of ten Kepler circumbinary planets to do so.

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arXiv2014

Masses of the components of SB2 binaries observed with Gaia. I. Selection of the sample and mass ratios of 20 new SB2s discovered with Sophie

In anticipation of the Gaia astrometric mission, a large sample of spectroscopic binaries is being observed since 2010 with the Sophie spectrograph at the Haute--Provence Observatory. Our aim is to derive the orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy sufficient to finally obtain the masses of the components with relative errors as small as 1% when the astrometric measurements of Gaia are taken into account. Simultaneously, the luminosities of the components in the Gaia photometric band G will also be obtained. Our observation program started with 200 SBs, including 152 systems that were only known as single-lined. Thanks to the high efficiency of the Sophie spectrograph, an additional component was found for 25 SBs. After rejection of 5 multiple systems, 20 new SB2s were retained, including 8 binaries with evolved primary, and their mass ratios were derived. Our final sample contains 68 SB2s, including 2 late-type giants and 10 other evolved stars.

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arXiv2014

Rotation Periods of 34,030 Kepler Main-Sequence Stars: The Full Autocorrelation Sample

We analyzed 3 years of data from the Kepler space mission to derive rotation periods of main-sequence stars below 6500 K. Our automated autocorrelation-based method detected rotation periods between 0.2 and 70 days for 34,030 (25.6%) of the 133,030 main-sequence Kepler targets (excluding known eclipsing binaries and Kepler Objects of Interest), making this the largest sample of stellar rotation periods to date. In this paper we consider the detailed features of the now well-populated period-temperature distribution and demonstrate that the period bimodality, first seen by McQuillan, Aigrain & Mazeh (2013) in the M-dwarf sample, persists to higher masses, becoming less visible above 0.6 M_sun. We show that these results are globally consistent with the existing ground-based rotation-period data and find that the upper envelope of the period distribution is broadly consistent with a gyrochronological age of 4.5 Gyrs, based on the isochrones of Barnes (2007), Mamajek & Hillenbrand (2008) and Meibom et al. (2009). We also performed a detailed comparison of our results to those of Reinhold et al. (2013) and Nielsen et al. (2013), who have measured rotation periods of field stars observed by Kepler. We examined the amplitude of periodic variability for the stars with detected rotation periods, and found a typical range between ~950 ppm (5th percentile) and ~22,700 ppm (95th percentile), with a median of ~5,600 ppm. We found typically higher amplitudes for shorter periods and lower effective temperatures, with an excess of low-amplitude stars above ~5400 K.

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arXiv2014

Kepler-413b: a slightly misaligned, Neptune-size transiting circumbinary planet

We report the discovery of a transiting, Rp = 4.347+/-0.099REarth, circumbinary planet (CBP) orbiting the Kepler K+M Eclipsing Binary (EB) system KIC 12351927 (Kepler-413) every ~66 days on an eccentric orbit with ap = 0.355+/-0.002AU, ep = 0.118+/-0.002. The two stars, with MA = 0.820+/-0.015MSun, RA = 0.776+/-0.009RSun and MB = 0.542+/-0.008MSun, RB = 0.484+/-0.024RSun respectively revolve around each other every 10.11615+/-0.00001 days on a nearly circular (eEB = 0.037+/-0.002) orbit. The orbital plane of the EB is slightly inclined to the line of sight (iEB = 87.33+/-0.06 degrees) while that of the planet is inclined by ~2.5 degrees to the binary plane at the reference epoch. Orbital precession with a period of ~11 years causes the inclination of the latter to the sky plane to continuously change. As a result, the planet often fails to transit the primary star at inferior conjunction, causing stretches of hundreds of days with no transits (corresponding to multiple planetary orbital periods). We predict that the next transit will not occur until 2020. The orbital configuration of the system places the planet slightly closer to its host stars than the inner edge of the extended habitable zone. Additionally, the orbital configuration of the system is such that the CBP may experience Cassini-States dynamics under the influence of the EB, in which the planet's obliquity precesses with a rate comparable to its orbital precession. Depending on the angular precession frequency of the CBP, it could potentially undergo obliquity fluctuations of dozens of degrees (and complex seasonal cycles) on precession timescales.

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arXiv2013

Kepler's Unparalleled Exploration of the Time Dimension

We show that the Kepler spacecraft in two-reaction wheel mode of operation is very well suited for the study of eclipsing binary star systems. Continued observations of the Kepler field will provide the most enduring and long-term valuable science. It will enable the discovery and characterization of eclipsing binaries with periods greater than 1 year - these are the most important, yet least understood binaries for habitable-zone planet background considerations. The continued mission will also enable the investigation of hierarchical multiple systems (discovered through eclipse timing variations), and provide drastically improved orbital parameters for circumbinary planetary systems.

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arXiv2013

A Habitable Zone Census via Transit Timing and the Imperative for Continuing to Observe the Kepler Field

We propose a scientific program to complete a census of planets, characterizing their masses, orbital properties, and dynamical histories using continued observations of the Kepler field of view with the Kepler spacecraft in a two reaction wheel mission. Even with a significantly reduced photometric precision, extending time-domain observations of this field is uniquely capable of pursuing several critical science goals: 1) measuring the architectures of planetary systems by identifying non-transiting planets interleaved among known transiting planets, 2) establishing the mass-radius relationship for planets in the important transition region between small, gas-rich sub-Neptune planets and large, rocky super-Earths, and 3) uncovering dynamical evidence of the formation and evolution of the inner regions of planetary systems. To meet these objectives, the unique multi-object observing capabilities of Kepler will be used in a set of concurrent campaigns with specific motivations. These campaigns focus largely on the ability to interpret Transit Timing Variations (TTVs) that result from dynamical interactions among planets in a system and include: 1) observations of systems that exhibit large TTVs and are particularly rich in dynamical information, 2) observations of systems where additional transit times will yield mass measurements of the constituent planets, 3) observations of systems where the TTV signal evolves over very long timescales, and 4) observations of systems with long-period planet candidates where additional transits will remove orbital period ambiguities caused by gaps in the original Kepler data.

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arXiv2013

Stellar Rotation Periods of the Kepler Objects of Interest: A Dearth of Close-in Planets around Fast Rotators

We present a large sample of stellar rotation periods for Kepler Objects of Interest (KOIs), based on three years of public Kepler data. These were measured by detecting periodic photometric modulation caused by star spots, using an algorithm based on the autocorrelation function (ACF) of the light curve, developed recently by McQuillan, Aigrain & Mazeh (2013). Of the 1919 main-sequence exoplanet hosts analyzed, robust rotation periods were detected for 737. Comparing the detected stellar periods to the orbital periods of the innermost planet in each system reveals a notable lack of close-in planets around rapid rotators. It appears that only slowly spinning stars, with rotation periods longer than 5-10 days, host planets on orbits shorter than 3 days, although the mechanism(s) that lead(s) to this is not clear.

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arXiv2013

Transit Timing Observations from Kepler. VIII Catalog of Transit Timing Measurements of the First Twelve Quarters

Following Ford et al. (2011, 2012) and Steffen et al. (2012) we derived the transit timing of 1960 Kepler KOIs using the pre-search data conditioning (PDC) light curves of the first twelve quarters of the Kepler data. For 721 KOIs with large enough SNRs, we obtained also the duration and depth of each transit. The results are presented as a catalog for the community to use. We derived a few statistics of our results that could be used to indicate significant variations. Including systems found by previous works, we have found 130 KOIs that showed highly significant TTVs, and 13 that had short-period TTV modulations with small amplitudes. We consider two effects that could cause apparent periodic TTV - the finite sampling of the observations and the interference with the stellar activity, stellar spots in particular. We briefly discuss some statistical aspects of our detected TTVs. We show that the TTV period is correlated with the orbital period of the planet and with the TTV amplitude.

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arXiv2013

BEER analysis of Kepler and CoRoT light curves: I. Discovery of Kepler-76b: A hot Jupiter with evidence for superrotation

We present the first case in which the BEER algorithm identified a hot Jupiter in the Kepler light curve, and its reality was confirmed by orbital solutions based on follow-up spectroscopy. The companion Kepler-76b was identified by the BEER algorithm, which detected the BEaming (sometimes called Doppler boosting) effect together with the Ellipsoidal and Reflection/emission modulations (BEER), at an orbital period of 1.54 days, suggesting a planetary companion orbiting the 13.3 mag F star. Further investigation revealed that this star appeared in the Kepler eclipsing binary catalog with estimated primary and secondary eclipse depths of 5e-3 and 1e-4 respectively. Spectroscopic radial-velocity follow-up observations with TRES and SOPHIE confirmed Kepler-76b as a transiting 2.0+/-0.26 Mjup hot Jupiter. The mass of a transiting planet can be estimated from either the beaming or the ellipsoidal amplitude. The ellipsoidal-based mass estimate of Kepler-76b is consistent with the spectroscopically measured mass while the beaming-based estimate is significantly inflated. We explain this apparent discrepancy as evidence for the superrotation phenomenon, which involves eastward displacement of the hottest atmospheric spot of a tidally-locked planet by an equatorial super-rotating jet stream. This phenomenon was previously observed only for HD 189733b in the infrared. We show that a phase shift of 10.3+/-2.0 degrees of the planet reflection/emission modulation, due to superrotation, explains the apparently inflated beaming modulation, resolving the ellipsoidal/beaming amplitude discrepancy. Kepler-76b is one of very few confirmed planets in the Kepler light curves that show BEER modulations and the first to show superrotation evidence in the Kepler band. Its discovery illustrates for the first time the ability of the BEER algorithm to detect short-period planets and brown dwarfs.

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arXiv2013

Measuring the rotation period distribution of field M-dwarfs with Kepler

We have analysed 10 months of public data from the Kepler space mission to measure rotation periods of main-sequence stars with masses between 0.3 and 0.55 M_sun. To derive the rotational period we introduce the autocorrelation function and show that it is robust against phase and amplitude modulation and residual instrumental systematics. Of the 2483 stars examined, we detected rotation periods in 1570 (63.2%), representing an increase of a factor ~ 30 in the number of rotation period determination for field M-dwarfs. The periods range from 0.37-69.7 days, with amplitudes ranging from 1.0-140.8 mmags. The rotation period distribution is clearly bimodal, with peaks at ~ 19 and ~ 33 days, hinting at two distinct waves of star formation, a hypothesis that is supported by the fact that slower rotators tend to have larger proper motions. The two peaks of the rotation period distribution form two distinct sequences in period-temperature space, with the period decreasing with increasing temperature, reminiscent of the Vaughan-Preston gap. The period-mass distribution of our sample shows no evidence of a transition at the fully convective boundary. On the other hand, the slope of the upper envelope of the period-mass relation changes sign around 0.55 M_sun, below which period rises with decreasing mass.

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arXiv2012

SDSS 1355+0856: A detached white dwarf + M star binary in the period gap discovered by the SWARMS survey

SDSS 1355+0856 was identified as a hot white dwarf (WD) with a binary companion from time-resolved SDSS spectroscopy as part of the ongoing SWARMS survey. Follow-up observations with the ARC 3.5m telescope and the MMT revealed weak emission lines in the central cores of the Balmer absorption lines during some phases of the orbit, but no line emission during other phases. This can be explained if SDSS 1355+0856 is a detached WD+M dwarf binary similar to GD 448, where one of the hemispheres of the low-mass companion is irradiated by the proximity of the hot white dwarf. Based on the available data, we derive a period of 0.11438 +- 0.00006 days, a primary mass of 0.46 +- 0.01 solar masses, a secondary mass between 0.083 and 0.097 solar masses, and an inclination larger than 57 degrees. This makes SDSS 1355+0856 one of the shortest period post-common envelope WD+M dwarf binaries known, and one of only a few where the primary is likely a He-core white dwarf, which has interesting implications for our understanding of common envelope evolution and the phenomenology of cataclysmic variables. The short cooling time of the WD (25 Myr) implies that the system emerged from the common envelope phase with a period very similar to what we observe today, and was born in the period gap of cataclysmic variables.

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arXiv2012

Detection of Neptune-size planetary candidates with CoRoT data. Comparison with the planet occurrence rate derived from Kepler

[Abridged] Context. The CoRoT space mission has been searching for transiting planets since the end of December 2006. Aims. We aim to investigate the capability of CoRoT to detect small-size transiting planets in short-period orbits, and to compare the number of CoRoT planets with 2 \leq R_p \leq 4 Rearth with the occurrence rate of small-size planets provided by the distribution of Kepler planetary candidates (Howard et al. 2012). Methods. We performed a test that simulates transits of super-Earths and Neptunes in real CoRoT light curves and searches for them blindly by using the LAM transit detection pipeline. Results. The CoRoT detection rate of planets with radius between 2 and 4 Rearth and orbital period P \leq 20 days is 59% (31%) around stars brighter than r'=14.0 (15.5). By properly taking the CoRoT detection rate for Neptune-size planets and the transit probability into account, we found that according to the Kepler planet occurrence rate, CoRoT should have discovered 12 \pm 2 Neptunes orbiting G and K dwarfs with P \leq 17 days in six observational runs. This estimate must be compared with the validated Neptune CoRoT-24b and five CoRoT planetary candidates in the considered range of planetary radii. We thus found a disagreement with expectations from Kepler at 3 σor 5 σ, assuming a blend fraction of 0% (six Neptunes) and 100% (one Neptune) for these candidates. Conclusions. This underabundance of CoRoT Neptunes with respect to Kepler may be due to several reasons. Regardless of the origin of the disagreement, which needs to be investigated in more detail, the noticeable deficiency of CoRoT Neptunes at short orbital periods seems to indirectly support the general trend found in Kepler data, i.e. that the frequency of small-size planets increases with increasing orbital periods and decreasing planet radii.

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arXiv2012

Kepler-47: A Transiting Circumbinary Multi-Planet System

We report the detection of Kepler-47, a system consisting of two planets orbiting around an eclipsing pair of stars. The inner and outer planets have radii 3.0 and 4.6 times that of the Earth, respectively. The binary star consists of a Sun-like star and a companion roughly one-third its size, orbiting each other every 7.45 days. With an orbital period of 49.5 days, eighteen transits of the inner planet have been observed, allowing a detailed characterization of its orbit and those of the stars. The outer planet's orbital period is 303.2 days, and although the planet is not Earth-like, it resides within the classical "habitable zone", where liquid water could exist on an Earth-like planet. With its two known planets, Kepler-47 establishes that close binary stars can host complete planetary systems.

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