An Analysis of Transiting Hot Jupiters Observed with K2: WASP-55b and WASP-75b
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We present our analysis of the K2 short-cadence data of two previously known hot Jupiter exoplanets: WASP-55b and WASP-75b. The high precision of the K2 lightcurves enabled us to search for transit timing and duration variations, rotational modulation, starspots, phase-curve variations and additional transiting planets. We identified stellar variability in the WASP-75 lightcurve which may be an indication of rotational modulation, with an estimated period of $11.2\pm1.5$ days. We combined this with the spectroscopically measured $v\sin(i_*)$ to calculate a possible line of sight projected inclination angle of $i_*=41\pm16^{\circ}$. We also perform a global analysis of K2 and previously published data to refine the system parameters.Keywords:
Hot Jupiter
Starspot
Rotation period
Wide-field high precision photometric surveys such as Kepler have produced reams of data suitable for investigating stellar magnetic activity of cooler stars. Starspot activity produces quasi-sinusoidal light curves whose phase and amplitude vary as active regions grow and decay over time. Here we investigate, firstly, whether there is a correlation between the size of starspots - assumed to be related to the amplitude of the sinusoid - and their decay timescale and, secondly, whether any such correlation depends on the stellar effective temperature. To determine this, we computed the autocorrelation functions of the light curves of samples of stars from Kepler and fitted them with apodised periodic functions. The light curve amplitudes, representing spot size were measured from the root-mean-squared scatter of the normalised light curves. We used a Monte Carlo Markov Chain to measure the periods and decay timescales of the light curves. The results show a correlation between the decay time of starspots and their inferred size. The decay time also depends strongly on the temperature of the star. Cooler stars have spots that last much longer, in particular for stars with longer rotational periods. This is consistent with current theories of diffusive mechanisms causing starspot decay. We also find that the Sun is not unusually quiet for its spectral type - stars with solar-type rotation periods and temperatures tend to have (comparatively) smaller starspots than stars with mid-G or later spectral types.
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New analyses are presented for published light curves of the eclipsing binary Algol which incorporate improved values of the mass ratio, primary temperature, and third light that have become available since the last published analyses of this system. Separate solutions were calculated for selected light curves in order to identify those that do not yield good solutions for the properties of the stars because of problems with the observations or because they are distorted by the effects of cirumstellar material or starspots. It is found that Wilson et al.'s (1972) 435-nm and V light curves are the only ones in the sample that can be used to solve for the properties of the stars in the system. These results are in good agreement with those from earlier analyses, and the properties of the system now seem to be firmly established.
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Aims. I aim to investigate whether the photometric variability in the candidate host star CVSO 30 can be explained by starspots. Methods. The Transiting Exoplanet Survey Satellite (TESS) light curve of CVSO 30 is separated into two independent non-sinusoidal periodic components. A starspot modelling technique is applied to each of these components. Results. Combined, the two model light curves reproduce the TESS observations to a high accuracy, obviating the need to invoke planetary transits to describe part of the variability.
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The NASA Kepler mission yields an unprecedented amount of data in the form of photometric light curves. Apart from valuable information on exoplanets and stellar pulsations, the light curves contain rotation signals from starspots crossing the stellar disk. These modulations of the light curves are modeled and 105 simulations are carried out to analyze and understand a similar analysis of the Kepler light curves. The periodogram is calculated for each light curve. Under the assumption that the main source of variability at periods >1 day is due to spots, the simulations show that the rotation period can be easily determined for spot lifetimes of 30–60 days, but becomes more unreliable for spots lifetimes of 10–20 days. The amplitude of the periodogram peaks appear to be only weakly dependent on changes in the size of the spots, while the width of the peaks shows no clear change with increasing spot lifetimes (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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Light curves describe the luminosity, or flux, emitted by celestial bodies or systems over a period of time. Since light curves are mostly irregular and may contain spikes and dips caused by extraneous factors, they contain valuable information about various phenomena and trends in the observed planetary system. For instance, light curves often help detect exoplanets in a stars planetary system. Furthermore, they also help characterize solar flares, cataclysmic variables (CVs), and various other phenomena. This study collects data in the form of light curves from stars in planetary systems housing terrestrial exoplanets found on the NASA Exoplanet Catalog and explored various causes for variations in the planetary systems light curve. One significant finding from light curve analysis was the possible existence of instrumental noise on the Kepler telescope in quarter 10. However, a larger exoplanet sample size and a real significance test are required for confirmation. This study exemplifies the accessibility and therefore feasibility of gathering data, graphing, and analyzing light curves.
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Abstract A terrestrial planet’s rotation period is one of the key parameters that determines its climate and habitability. Current methods for detecting the rotation period of exoplanets are not suitable for terrestrial exoplanets. Here we demonstrate that, under certain conditions, the rotation period of an Earth-like exoplanet will be detectable using direct-imaging techniques. We use a global climate model that includes clouds to simulate reflected starlight from an Earth-like exoplanet and explore how different parameters (e.g., orbital geometry, wavelength, time resolution) influence the detectability of the planet’s rotation period. We show that the rotation period of an Earth-like exoplanet is detectable using visible-wavelength channels with time-series monitoring at a signal-to-noise ratio (S/N) >20 with ∼5–15 rotation periods of data, while the rotation period of a planet with full ocean coverage is unlikely to be detectable. To better detect the rotation period, one needs to plan the observation so that each individual integration would yield a S/N >10, while keeping the integration time shorter than 1/6 to 1/4 of the rotation period of the planet. Our results provide important guidance for rotation period detection of Earth-like exoplanets in reflected light using future space telescopes.
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view Abstract Citations (26) References (51) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Light Synthesis Program for Binary Stars. II. Light Curve and Color Curve Effects in a Contact System Linnell, A. P. Abstract This paper studies various models which attempt to explain light curves and color curves for eclipsing W Ursae Majoris stars of type W. Observed color curves for VW Cephei are in disagreement with the Mullan starspot model to explain W-type light curves. An alternative starspot model, with starspots located on the averted hemisphere of the larger star, represents the light curves and color curves for 1980 August 21 with good accuracy. The observed light curves and color curves of VW Cephei agree with theoretical curves for a Rucinski hot secondary model. A single spot, added to the underlying hot secondary model, provides a reasonably accurate representation of UBVRI photometric data. Publication: The Astrophysical Journal Pub Date: January 1986 DOI: 10.1086/163804 Bibcode: 1986ApJ...300..304L Keywords: Eclipsing Binary Stars; Light Curve; Starspots; Stellar Atmospheres; Stellar Color; Stellar Models; Hot Stars; Stellar Envelopes; Astrophysics; STARS: ATMOSPHERES; STARS: ECLIPSING BINARIES; STARS: W URSAE MAJORIS full text sources ADS | data products SIMBAD (4) Related Materials (2) Part 1: 1984ApJS...54...17L Part 3: 1989ApJ...342..449L
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