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Register a new userA New Spectroscopic and Photometric Analysis of the Transiting Planet Systems TrES-3 and TrES-4
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Alessandro Sozzetti
Publication date
2008
fields
Physics
and research's language is
English
Authors
A. Sozzetti
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We report new spectroscopic and photometric observations of the parent stars of the recently discovered transiting planets TrES-3 and TrES-4. A detailed abundance analysis based on high-resolution spectra yields [Fe/H] $= -0.19pm 0.08$, $T_mathrm{eff} = 5650pm 75$ K, and $log g = 4.4pm 0.1$ for TrES-3, and [Fe/H] $= +0.14pm 0.09$, $T_mathrm{eff} = 6200pm 75$ K, and $log g = 4.0pm0.1$ for TrES-4. The accuracy of the effective temperatures is supported by a number of independent consistency checks. The spectroscopic orbital solution for TrES-3 is improved with our new radial-velocity measurements of that system, as are the light-curve parameters for both systems based on newly acquired photometry for TrES-3 and a reanalysis of existing photometry for TrES-4. We have redetermined the stellar parameters taking advantage of the strong constraint provided by the light curves in the form of the normalized separation $a/R_star$ (related to the stellar density) in conjunction with our new temperatures and metallicities. The masses and radii we derive are $M_star=0.928_{-0.048}^{+0.028} M_{sun}$,$R_star = 0.829_{-0.022}^{+0.015} R_{sun}$, and $M_star = 1.404_{-0.134}^{+0.066} M_{sun}$, $R_star=1.846_{-0.087}^{+0.096} R_{sun}$ for TrES-3 and TrES-4, respectively. With these revised stellar parameters we obtain improved values for the planetary masses and radii. We find $M_p = 1.910_{-0.080}^{+0.075} M_mathrm{Jup}$, $R_p=1.336_{-0.036}^{+0.031} R_mathrm{Jup}$ for TrES-3, and $M_p=0.925 pm 0.082 M_mathrm{Jup}$, $R_p=1.783_{-0.086}^{+0.093} R_mathrm{Jup}$ for TrES-4. We confirm TrES-4 as the planet with the largest radius among the currently known transiting hot Jupiters.
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We report the detection of a transiting Jupiter-sized planet orbiting a relatively bright (V=11.79) K0V star. We detected the transit light-curve signature in the course of the TrES multi-site transiting planet survey, and confirmed the planetary nature of the companion via multicolor photometry and precise radial velocity measurements. We designate the planet TrES-1; its inferred mass is 0.75 +/- 0.07 Jupiter masses, its radius is 1.08 (+0.18/-0.04) Jupiter radii, and its orbital period is 3.030065 +/- 0.000008 days. This planet has an orbital period similar to that of HD 209458b, but about twice as long as those of the OGLE transiting planets. Its mass is indistinguishable from that of HD 209458b, but its radius is significantly smaller and fits the theoretical models without the need for an additional source of heat deep in the atmosphere, as has been invoked by some investigators for HD 209458b.
The aim of this work is a detailed analysis of transit light curves from TrES-1 and TrES-2, obtained over a period of three to four years, in order to search for variabilities in observed mid-transit times and to set limits for the presence of additional third bodies. Using the IAC 80cm telescope, we observed transits of TrES-1 and TrES-2 over several years. Based on these new data and previously published work, we studied the observed light curves and searched for variations in the difference between observed and calculated (based on a fixed ephemeris) transit times. To model possible transit timing variations, we used polynomials of different orders, simulated O-C diagrams corresponding to a perturbing third mass and sinusoidal fits. For each model we calculated the chi-squared residuals and the False Alarm Probability (FAP). For TrES-1 we can exclude planetary companions (>1 M_earth) in the 3:2 and 2:1 MMRs having high FAPs based on our transit observations from ground. Additionally, the presence of a light time effect caused by e. g. a 0.09 M_sun mass star at a distance of 7.8 AU is possible. As for TrES-2, we found a better ephemeris of Tc = 2,453,957.63512(28) + 2.4706101(18) x Epoch and a good fit for a sine function with a period of 0.2 days, compatible with a moon around TrES-2 and an amplitude of 57 s, but it was not a uniquely low chi-squared value that would indicate a clear signal. In both cases, TrES-1 and TrES-2, we were able to put upper limits on the presence of additional perturbers masses. We also conclude that any sinusoidal variations that might be indicative of exomoons need to be confirmed with higher statistical significance by further observations, noting that TrES-2 is in the field-of-view of the Kepler Space Telescope.
We investigate the origin of a flux increase found during a transit of TrES-1, observed with the HST. This feature in the HST light curve cannot be attributed to noise and is supposedly a dark area on the stellar surface of the host star eclipsed by TrES-1 during its transit. We investigate the likeliness of two possible hypothesis for its origin: A starspot or a second transiting planet. We made use of several transit observations of TrES-1 from space with the HST and from ground with the IAC-80 telescope. On the basis of these observations we did a statistical study of flux variations in each of the observed events, to investigate if similar flux increases are present in other parts of the data set. The HST observation presents a single clear flux rise during a transit whereas the ground observations led to the detection of two such events but with low significance. In the case of having observed a starspot in the HST data, assuming a central impact between the spot and TrES-1, we would obtain a lower limit for the spot radius of 42000 km. For this radius the spot temperature would be 4690 K, 560 K lower then the stellar surface of 5250 K. For a putative second transiting planet we can set a lower limit for its radius at 0.37 R$_J$ and for periods of less than 10.5 days, we can set an upper limit at 0.72 R$_J$. Assuming a conventional interpretation, then this HST observation constitutes the detection of a starspot. Alternatively, this flux rise might also be caused by an additional transiting planet. The true nature of the origin can be revealed if a wavelength dependency of the flux rise can be shown or discarded with a higher certainty. Additionally, the presence of a second planet can also be detected by radial velocity measurements.
With an equilibrium temperature of 1200 K, TrES-1 is one of the coolest hot Jupiters observed by {Spitzer}. It was also the first planet discovered by any transit survey and one of the first exoplanets from which thermal emission was directly observed. We analyzed all {Spitzer} eclipse and transit data for TrES-1 and obtained its eclipse depths and brightness temperatures in the 3.6 {micron} (0.083 % {pm} 0.024 %, 1270 {pm} 110 K), 4.5 {micron} (0.094 % {pm} 0.024 %, 1126 {pm} 90 K), 5.8 {micron} (0.162 % {pm} 0.042 %, 1205 {pm} 130 K), 8.0 {micron} (0.213 % {pm} 0.042 %, 1190 {pm} 130 K), and 16 {micron} (0.33 % {pm} 0.12 %, 1270 {pm} 310 K) bands. The eclipse depths can be explained, within 1$sigma$ errors, by a standard atmospheric model with solar abundance composition in chemical equilibrium, with or without a thermal inversion. The combined analysis of the transit, eclipse, and radial-velocity ephemerides gives an eccentricity $e = 0.033^{+0.015}_{-0.031}$, consistent with a circular orbit. Since TrES-1s eclipses have low signal-to-noise ratios, we implemented optimal photometry and differential-evolution Markov-chain Monte Carlo (MCMC) algorithms in our Photometry for Orbits, Eclipses, and Transits (POET) pipeline. Benefits include higher photometric precision and sim10 times faster MCMC convergence, with better exploration of the phase space and no manual parameter tuning.
We observed nine primary transits of the hot Jupiter TrES-3b in several optical and near-UV photometric bands from 2009 June to 2012 April in an attempt to detect its magnetic field. Vidotto, Jardine and Helling suggest that the magnetic field of TrES-3b can be constrained if its near-UV light curve shows an early ingress compared to its optical light curve, while its egress remains unaffected. Predicted magnetic field strengths of Jupiter-like planets should range between 8 G and 30 G. Using these magnetic field values and an assumed B_star of 100 G, the Vidotto et al. method predicts a timing difference of 5-11 min. We did not detect an early ingress in our three nights of near-UV observations, despite an average cadence of 68 s and an average photometric precision of 3.7 mmag. However, we determined an upper limit of TrES-3bs magnetic field strength to range between 0.013 and 1.3 G (for a 1-100 G magnetic field strength range for the host star, TrES-3) using a timing difference of 138 s derived from the Nyquist-Shannon sampling theorem. To verify our results of an abnormally small magnetic field strength for TrES-3b and to further constrain the techniques of Vidotto et al., we propose future observations of TrES-3b with other platforms capable of achieving a shorter near-UV cadence. We also present a refinement of the physical parameters of TrES-3b, an updated ephemeris and its first published near-UV light curve. We find that the near-UV planetary radius of Rp = 1.386+0.248-0.144 RJup is consistent with the planets optical radius.
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