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Title: Long-Term Transit Timing Monitoring and Refined Light Curve Parameters of HAT-P-13b
Authors: Benjamin J. Fulton, Avi Shporer, Joshua N. Winn, Matthew J. Holman, András Pál, J. Zachary Gazak
 
We present 10 new transit light curves of the transiting hot Jupiter HAT-P-13b, obtained during two observational seasons by three different telescopes. When combined with 12 previously published light curves, we have a sample consisting of 22 transit light curves, spanning 1,041 days across 4 observational seasons. We use this sample to examine the recently observed large-amplitude transit timing variations (Pal et al. 2011), and give refined system parameters. We find that the transit times are consistent with a linear ephemeris, with the exception of a single transit time, from UT 2009 Nov 5, for which the measured mid transit time significantly deviates from our linear ephemeris. The nature of this deviation is not clear, and the rest of the data does not show any significant transit timing variation.

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Title: TASTE. II. A new observational study of transit time variations in HAT-P-13b
Authors: V. Nascimbeni, G. Piotto, L. R. Bedin, M. Damasso, L. Malavolta, L. Borsato

TASTE (The Asiago Search for Transit timing variations of Exoplanets) project is collecting high-precision, short-cadence light curves for a selected sample of transiting exoplanets. The hot jupiter HAT-P-13b has been claimed to have suddenly deviated from a linear ephemeris by ~20 min, suggesting the presence of a perturber in the system. Using five new transits, we discuss the plausibility of this transit time variation (TTV), and show that a periodic signal should not be excluded. More follow-up observations are required to constrain the mass and the orbit of the hypotetical perturber.

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Title: An Analysis of Jitter and Transit Timing Variations in the HAT-P-13 System
Authors: Matthew J. Payne, Eric B. Ford

If the two planets in the HAT-P-13 system are coplanar, the orbital states provide a probe of the internal planetary structure. Previous analyses of radial velocity and transit timing data of the system suggested that the observational constraints on the orbital states were rather small. We reanalyse the available data, treating the jitter as an unknown MCMC parameter, and find that a wide range of jitter values are plausible, hence the system parameters are less well constrained than previously suggested. For slightly increased levels of jitter (~ 4.5\,m\,s^{-1}) the eccentricity of the inner planet can be in the range 0<e_{inner}<0.07, the period and eccentricity of the outer planet can be 440<P_{outer}<470 days and 0.55<e_{outer}<0.85 respectively, while the relative pericenter alignment, \eta, of the planets can take essentially any value -180°<\eta<+180°. It is therefore difficult to determine whether e_{inner} and \eta have evolved to a fixed-point state or a limit cycle, or to use e_{inner} to probe the internal planetary structure. We perform various transit timing variation (TTV) analyses, demonstrating that current constraints merely restrict e_{outer}<0.85, and rule out relative planetary inclinations within ~ 2° of i_{rel}=90°, but that future observations could significantly tighten the restriction on both these parameters. We demonstrate that TTV profiles can readily distinguish the theoretically favored inclinations of i_{rel}=0°\,&\,45°, provided that sufficiently precise and frequent transit timing observations of HAT-P-13b can be made close to the pericenter passage of HAT-P-13c. We note the relatively high probability that HAT-P-13c transits and suggest observational dates and strategies.

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Title: Transit timing variations in the HAT-P-13 planetary system
Authors: András Pál (1,2), Krisztián Sárneczky (1), Gyula M. Szabó (1,3), Attila Szing (1), László L. Kiss (1,4), György Mezö (1), Zsolt Regály (1) ((1) Konkoly Observatory of the Hungarian Academy of Sciences, (2) Department of Astronomy, Loránd Eötvös University, (3) Department of Experimental Physics and Astronomical Observatory, (4) Sydney Institute for Astronomy)

In this Letter we present observations of recent HAT-P-13b transits. The combined analysis of published and newly obtained transit epochs shows evidence for significant transit timing variations since the last publicly available ephemerides. Variation of transit timings result in a sudden switch of transit times. The detected full range of TTV spans ~0.015 days, which is significantly more than the known TTV events exhibited by hot Jupiters. If we have detected a periodic process, its period should be at least ~3 years because there are no signs of variations in the previous observations. This argument makes unlikely that the measured TTV is due to perturbations by HAT-P-13c.

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HAT-P-13 Exoplanetary System
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Title: The HAT-P-13 Exoplanetary System: Evidence for Spin-Orbit Alignment and a Third Companion
Authors: Joshua N. Winn, John Asher Johnson, Andrew W. Howard, Geoffrey W. Marcy, Gaspar A. Bakos, Joel Hartman, Guillermo Torres, Simon Albrecht, Norio Narita
(Version v2)

We present new radial-velocity measurements of HAT-P-13, a star with two previously known companions: a transiting giant planet "b" with an orbital period of 3 days, and a more massive object "c" on a 1.2 yr, highly eccentric orbit. For this system, dynamical considerations would lead to constraints on planet b's interior structure, if it could be shown that the orbits are coplanar and apsidally locked. By modelling the Rossiter-McLaughlin effect, we show that planet b's orbital angular momentum vector and the stellar spin vector are well-aligned on the sky (lambda = -0.9 ±8.5 deg), suggesting that the planetary orbits are also well-aligned. The refined orbital solution favours a slightly eccentric orbit for planet b (e = 0.0142_{-0.0044}^{+0.0052}), although it is not clear whether it is apsidally locked with c's orbit (\Delta\omega = 48_{-38}^{+25} deg). We find a long-term trend in the star's radial velocity and interpret it as evidence for an additional body "d", which may be another planet or a low-mass star. The next inferior conjunction of c, when a transit may happen, is expected on JD 2,455,315.2 ±1.9 (centred on UT 17h 2010 April 28).

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HAT-P-13
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Title: The HAT-P-13 Exoplanetary System: Evidence for Spin-Orbit Alignment and a Third Companion
Authors: Joshua N. Winn, John Asher Johnson, Andrew W. Howard, Geoffrey W. Marcy, Gaspar A. Bakos, Joel Hartman, Guillermo Torres, Simon Albrecht, Norio Narita

We present new radial-velocity measurements of HAT-P-13, a star with two previously known companions: a transiting giant planet "b" with an orbital period of 3 days, and a more massive object "c" on a 1.2 yr, highly eccentric orbit. For this system, dynamical considerations would lead to constraints on planet b's interior structure, if it could be shown that the orbits are coplanar and apsidally locked. By modelling the Rossiter-McLaughlin effect, we show that planet b's orbital angular momentum vector and the stellar spin vector are well-aligned on the sky (lambda = -0.9 ±8.5 deg), suggesting that the planetary orbits are also well-aligned. The refined orbital solution favours a slightly eccentric orbit for planet b (e = 0.0142_{-0.0044}^{+0.0052}), although it is not clear whether it is apsidally locked with c's orbit (\Delta\omega = 48_{-38}^{+25} deg). We find a long-term trend in the star's radial velocity and interpret it as evidence for an additional body "d", which may be another planet or a low-mass star. The next inferior conjunction of c, when a transit may happen, is expected on JD 2,455,315.2 ±1.9 (centred on UT 17h 2010 April 28).

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New Extrasolar System Allows Planetary 'X-Ray'
The discovery of two extrasolar planets orbiting the star HAT-P-13 will allow scientists to use one of them to "x-ray" the other to determine if it's got a rocky core.
Astronomers plan to use a large outer planet, HAT-P-13C, that transits the face of its sun, can be used to probe the internal structure of the smaller HAT-P-13B.
As the two planets pull on each other, they warp each other's orbits. By measuring how eccentric the orbits of the planets are, they can use some fancy, old-school math to determine how much of the interior planet's mass is located at its center. It's like a planetary laboratory 700 light-years away.

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Title: HAT-P-13b,c: a transiting hot Jupiter with a massive outer companion on an eccentric orbit
Authors: G. A. Bakos (1,2), A. W. Howard (3), R. W. Noyes (1), J. Hartman (1), G. Torres (1), Geza Kovacs (4), D. A. Fischer (5), D. W. Latham (1), J. A. Johnson (6), G. W. Marcy (3), D. D. Sasselov (1), R. P. Stefanik (1), B. Sipocz (1,7), Gabor Kovacs (1), G. A. Esquerdo (1), A. Pal (4,1), J. Lazar (8), I. Papp (8) ((1) CfA, (2) NSF Fellow, (3) UCB, (4) Konkoly Observatory, (5) SFSU, (6) IfA, (7) Department of Astronomy, ELTE, (8) Hungarian Astronomical Association.)
(Version v2)

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Title: HAT-P-13b,c: a transiting hot Jupiter with a massive outer companion on an eccentric orbit
Authors: G. A. Bakos (1,2), A. W. Howard (3), R. W. Noyes (1), J. Hartman (1), G. Torres (1), Geza Kovacs (4), D. A. Fischer (5), D. W. Latham (1), J. A. Johnson (6), G. W. Marcy (3), D. D. Sasselov (1), R. P. Stefanik (1), B. Sipocz (1,7), Gabor Kovacs (1), G. A. Esquerdo (1), A. Pal (4,1), J. Lazar (8), I. Papp (8) ((1) CfA, (2) NSF Fellow, (3) UCB, (4) Konkoly Observatory, (5) SFSU, (6) IfA, (7) Department of Astronomy, ELTE, (8) Hungarian Astronomical Association.)

We report on the discovery of a planetary system with a close-in transiting hot Jupiter on a near circular orbit and a massive outer planet on a highly eccentric orbit. The inner planet, HAT-P-13b, transits the bright V=10.622 G4 dwarf star GSC 3416-00543 every P = 2.916260 ±0.000010 days, with transit epoch Tc = 2454779.92979 ±0.00038 (BJD) and duration 0.1345 ±0.0017 d. The outer planet, HAT-P-13c orbits the star with P2 = 428.5 ±3.0 days and nominal transit center (assuming zero impact parameter) of T2c = 2454870.4 ±1.8 (BJD) or time of periastron passage T2,peri= 2454890.05 ±0.48 (BJD). Transits of the outer planet have not been observed, and may not be present. The host star has a mass of 1.22+0.05-0.10Msun, radius of 1.56 ±0.08 Rsun, effective temperature 5638 ±90K, and is rather metal rich with [Fe/H] = +0.43±0.08. The inner planetary companion has a mass of 0.851+/0.029-/0.046 Mjup, and radius of 1.280±0.079 Rjup yielding a mean density of 0.499+/0.103-/0.069 gcm-3 . The outer companion has m_2sini_2 = 15.2±1.0 Mjup, and orbits on a highly eccentric orbit of e2 = 0.691 ±0.018. While we have not detected significant transit timing variations of HAT-P-13b, due to gravitational and light-travel time effects, future observations will constrain the orbital inclination of HAT-P-13c, along with its mutual inclination to HAT-P-13b. The HAT-P-13 (b,c) double-planet system may prove extremely valuable for theoretical studies of the formation and dynamics of planetary systems.

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