A few studies have reported a significant dearth of exoplanets with Neptune mass and radius with orbital periods below 2–4 d. This cannot be explained by observational biases because many Neptunian ...planets with longer orbital periods have been detected. The existence of this desert is similar to the appearance of the so-called brown-dwarf desert that suggests different formation mechanisms of planets and stellar companions with short orbital periods. Similarly, the Neptunian desert might indicate different mechanisms of formation and evolution for hot Jupiters and short-period super-Earths. We here follow a previous study and examine the location and shape of the desert in both the period-mass and period-radius planes, using the currently available large samples of planets. The desert in the period-mass plane has a relatively sharp upper edge, with a planetary mass that is inversely proportional to the planetary orbital period, while the lower, somewhat blurred, boundary is located along masses that are apparently linearly proportional to the period. The desert in the period-radius plane of the transiting planets is less clear. It seems as if the radius along the upper boundary is inversely proportional to the period to the power of one-third, while the lower boundary shows a radius that is proportional to the period to the power of two-thirds. The combination of the two upper bounds of the desert, in the period-mass and period-radius planes, yields a planetary mass-radius relation of Rp/RJup ≃ (1.2 ± 0.3)(Mp/MJup)0.27 ± 0.11 for 0.1 ≲ Mp/MJup ≲ 1. The derived shape of the desert, which might extend up to periods of 5–10 d, could shed some light on the formation and evolution of close-in planets.
We analyzed three 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 et al. in the M-dwarf sample, persists to higher masses, becoming less visible above 0.6 M sub(middot in circle). 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 Gyr, based on the isochrones of Barnes, Mamajek, & Hillenbrand and Meibom et al. We also performed a detailed comparison of our results to those of Reinhold et al. and Nielsen et al., who measured rotation periods of field stars observed by Kepler. We examined the amplitude of periodic variability for the stars with detection rotation periods, and found a typical range between ~950 ppm (5th percentile) and ~22,700 ppm (95th percentile), with a median of ~5600 ppm. We found typically higher amplitudes for shorter periods and lower effective temperatures, with an excess of low-amplitude stars above ~5400 K.
We present a simple algorithm, BEER, to search for a combination of the BEaming, Ellipsoidal and the Reflection/heating periodic modulations, induced by short-period non-transiting low-mass ...companions. The beaming effect is due to the increase (decrease) in the brightness of any light source approaching (receding from) the observer. To first order, the beaming and the reflection/heating effects modulate the stellar brightness at the orbital period, with phases separated by a quarter of a period, whereas the ellipsoidal effect is modulated with the orbital first harmonic. The phase and harmonic differences between the three modulations allow the algorithm to search for a combination of the three effects and identify stellar candidates for low-mass companions. The paper presents the algorithm, including an assignment of a likelihood factor to any possible detection, based on the expected ratio of the beaming and ellipsoidal effects, given an order-of-magnitude estimate of the three effects. As predicted by Loeb & Gaudi and by Zucker, Mazeh & Alexander, the Kepler and the CoRoT light curves are precise enough to allow detection of massive planets and brown-dwarf/low-mass-stellar companions with orbital period up to 10-30 days. To demonstrate the feasibility of the algorithm, we present two examples of candidates found in the first 33 days of the Q1 Kepler light curves. Although we used a relatively short time-span, the light curves were precise enough to enable the detection of periodic effects with amplitudes as small as one part in 104 of the stellar flux.
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. 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 per cent), representing an increase of a factor of ∼30 in the number of rotation period determination for field M dwarfs. The periods range from 0.37 to 69.7 d, with amplitudes ranging from 1.0 to 140.8 mmag. The rotation period distribution is clearly bimodal, with peaks at ∼19 and ∼33 d, 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, below which period rises with decreasing mass.
We present a large sample of stellar rotation periods for Kepler Objects of Interest, 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 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 2 or 3 days, although the mechanism(s) that lead(s) to this is not clear.
CoRoT-3b is a 22 Jupiter-mass massive-planet/brown-dwarf object, orbiting an F3-star with a period of 4.3 days. We analyzed the out-of-transit CoRoT-3 red-channel lightcurve obtained by the CoRoT ...mission and detected the ellipsoidal modulation, with half the orbital period and an amplitude of 59 ± 9 ppm (parts per million), and the relativistic beaming effect, with the orbital period and an amplitude of 27 ± 9 ppm. Phases and amplitudes of both modulations are consistent with our theoretical approximation.
ABSTRACT
Analysis of APOGEE DR12 stellar radial velocities by Troup et al. affirmed the existence of the well-known brown-dwarf desert (BDD). They detected a dearth of spectroscopic binaries (SB) ...with periods shorter than ∼10–30 d and secondaries with masses in the range of ∼0.01–$0.1\, \mathrm{M}_{\odot }$. We reconsider here their sample of binaries, focusing on 116 systems on the main sequence of the Gaia colour–magnitude diagram, with mostly K-dwarf primaries. Using our recently devised algorithm to analyse the mass-ratio distribution of a sample of SBs we confirm the BDD existence and delineate its boundaries. For the K-dwarf APOGEE 1–25 d binaries, the companion-mass range of the BDD is ∼0.02–$0.2\, \mathrm{M}_{\odot }$. The mass-ratio distribution of the long-period (25–500 d) binaries does not show any dearth at the q range studied. Instead, their distribution displays a linear increase in log q, implying a tendency towards low-q values. The limits of the BDD do not coincide with the frequently used mass limits of the brown-dwarf population, sometimes defined as 0.013 and $0.08\, \mathrm{M}_{\odot }$, based on theoretically derived stellar minimum masses for burning deuterium and hydrogen in their cores. Trying to draw the boundaries of the desert, we suggest either a wedged or trapezoidal shape. We discuss briefly different scenarios that can account for the formation of the BDD, in terms of differentiating between stellar secondaries and planets in particular, and compare this desert to the Neptunian desert that can distinguish between Jovian planets and super-Earths of short periods.
We suggest a new algorithm to remove systematic effects in a large set of light curves obtained by a photometric survey. The algorithm can remove systematic effects, such as those associated with ...atmospheric extinction, detector efficiency, or point spread function changes over the detector. The algorithm works without any prior knowledge of the effects, as long as they linearly appear in many stars of the sample. The approach, which was originally developed to remove atmospheric extinction effects, is based on a lower rank approximation of matrices, an approach which has already been suggested and used in chemometrics, for example. The proposed algorithm is especially useful in cases where the uncertainties of the measurements are unequal. For equal uncertainties, the algorithm reduces to the Principal Component Analysis (PCA) algorithm. We present a simulation to demonstrate the effectiveness of the proposed algorithm and we point out its potential, in the search for transit candidates in particular.
ABSTRACT
Preparing for the expected wealth of Gaia detections, we consider here a simple algorithm for classifying unresolved astrometric binaries with main-sequence (MS) primary into three classes: ...binaries with a probable MS secondary, with two possible values for the mass ratio; probable hierarchical triple MS systems with an astrometric secondary as a close binary, with a limited range of mass-ratio values; and binaries with a compact-object secondary, with a minimal value of the mass ratio. This is done by defining a unitless observational parameter ‘Astrometric Mass-Ratio Function’ (AMRF), $\mathcal {A}$, of a binary, based on primary-mass estimation, in addition to the astrometric parameters – the angular semimajor axis, the period, and the parallax. We derive the $\mathcal {A}$ value that differentiates the three classes by forward modelling representative binaries of each class, assuming some mass–luminosity relation. To demonstrate the potential of the algorithm, we consider the orbits of 98 Hipparcos astrometric binaries with MS primaries, using the Hipparcos parallaxes and the primary-mass estimates. For systems with known spectroscopic orbital solution, our results are consistent with the spectroscopic elements, validating the suggested approach. The algorithm will be able to identify hierarchical triple systems and dormant neutron star and black hole companions in the Gaia astrometric binaries.
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