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Title: Planet-induced Stellar Pulsations in HAT-P-2's Eccentric System

Abstract

Extrasolar planets on eccentric short-period orbits provide a laboratory in which to study radiative and tidal interactions between a planet and its host star under extreme forcing conditions. Studying such systems probes how the planet’s atmosphere redistributes the time-varying heat flux from its host and how the host star responds to transient tidal distortion. Here, we report the insights into the planet–star interactions in HAT-P-2's eccentric planetary system gained from the analysis of ∼350 hr of 4.5 μ m observations with the Spitzer Space Telescope . The observations show no sign of orbit-to-orbit variability nor of orbital evolution of the eccentric planetary companion, HAT-P-2 b. The extensive coverage allows us to better differentiate instrumental systematics from the transient heating of HAT-P-2 b’s 4.5 μ m photosphere and yields the detection of stellar pulsations with an amplitude of approximately 40 ppm. These pulsation modes correspond to exact harmonics of the planet’s orbital frequency, indicative of a tidal origin. Transient tidal effects can excite pulsation modes in the envelope of a star, but, to date, such pulsations had only been detected in highly eccentric stellar binaries. Current stellar models are unable to reproduce HAT-P-2's pulsations, suggesting that our understanding of the interactionsmore » at play in this system is incomplete.« less

Authors:
 [1];  [2]; ;  [3];  [4];  [5];  [6];  [7];  [8];  [9];  [10];  [11];  [12];  [13];  [14];  [15]
  1. Department of Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)
  2. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
  3. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States)
  4. TAPIR, Walter Burke Institute for Theoretical Physics, Mailcode 350-17, California Institute of Technology, Pasadena, CA 91125 (United States)
  5. Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark)
  6. Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States)
  7. Department of Astronomy, Yale University, New Haven, CT 06511 (United States)
  8. Department of Astronomy, University of Maryland at College Park, College Park, MD 20742 (United States)
  9. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91009 (United States)
  10. Department of Physics, Department of Earth and Planetary Sciences, McGill University, 3550 rue University, Montreal, QC H3A 2A7 (Canada)
  11. Department of Astronomy, University of Washington, Seattle, WA 98195 (United States)
  12. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
  13. Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
  14. Department of Physics, Principia College, Elsah, IL 62028 (United States)
  15. Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States)
Publication Date:
OSTI Identifier:
22654539
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 836; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; APPROXIMATIONS; DETECTION; EVOLUTION; GAIN; HEAT; HEAT FLUX; HEATING; INTERACTIONS; ORBITS; PHOTOSPHERE; PLANETS; PULSATIONS; SATELLITE ATMOSPHERES; SATELLITES; SPACE; STABILITY; STARS; TELESCOPES

Citation Formats

Wit, Julien de, Lewis, Nikole K., Knutson, Heather A., Batygin, Konstantin, Fuller, Jim, Antoci, Victoria, Fulton, Benjamin J., Laughlin, Gregory, Deming, Drake, Shporer, Avi, Cowan, Nicolas B., Agol, Eric, Burrows, Adam S., Fortney, Jonathan J., Langton, Jonathan, and Showman, Adam P.. Planet-induced Stellar Pulsations in HAT-P-2's Eccentric System. United States: N. p., 2017. Web. doi:10.3847/2041-8213/836/2/L17.
Wit, Julien de, Lewis, Nikole K., Knutson, Heather A., Batygin, Konstantin, Fuller, Jim, Antoci, Victoria, Fulton, Benjamin J., Laughlin, Gregory, Deming, Drake, Shporer, Avi, Cowan, Nicolas B., Agol, Eric, Burrows, Adam S., Fortney, Jonathan J., Langton, Jonathan, & Showman, Adam P.. Planet-induced Stellar Pulsations in HAT-P-2's Eccentric System. United States. doi:10.3847/2041-8213/836/2/L17.
Wit, Julien de, Lewis, Nikole K., Knutson, Heather A., Batygin, Konstantin, Fuller, Jim, Antoci, Victoria, Fulton, Benjamin J., Laughlin, Gregory, Deming, Drake, Shporer, Avi, Cowan, Nicolas B., Agol, Eric, Burrows, Adam S., Fortney, Jonathan J., Langton, Jonathan, and Showman, Adam P.. Mon . "Planet-induced Stellar Pulsations in HAT-P-2's Eccentric System". United States. doi:10.3847/2041-8213/836/2/L17.
@article{osti_22654539,
title = {Planet-induced Stellar Pulsations in HAT-P-2's Eccentric System},
author = {Wit, Julien de and Lewis, Nikole K. and Knutson, Heather A. and Batygin, Konstantin and Fuller, Jim and Antoci, Victoria and Fulton, Benjamin J. and Laughlin, Gregory and Deming, Drake and Shporer, Avi and Cowan, Nicolas B. and Agol, Eric and Burrows, Adam S. and Fortney, Jonathan J. and Langton, Jonathan and Showman, Adam P.},
abstractNote = {Extrasolar planets on eccentric short-period orbits provide a laboratory in which to study radiative and tidal interactions between a planet and its host star under extreme forcing conditions. Studying such systems probes how the planet’s atmosphere redistributes the time-varying heat flux from its host and how the host star responds to transient tidal distortion. Here, we report the insights into the planet–star interactions in HAT-P-2's eccentric planetary system gained from the analysis of ∼350 hr of 4.5 μ m observations with the Spitzer Space Telescope . The observations show no sign of orbit-to-orbit variability nor of orbital evolution of the eccentric planetary companion, HAT-P-2 b. The extensive coverage allows us to better differentiate instrumental systematics from the transient heating of HAT-P-2 b’s 4.5 μ m photosphere and yields the detection of stellar pulsations with an amplitude of approximately 40 ppm. These pulsation modes correspond to exact harmonics of the planet’s orbital frequency, indicative of a tidal origin. Transient tidal effects can excite pulsation modes in the envelope of a star, but, to date, such pulsations had only been detected in highly eccentric stellar binaries. Current stellar models are unable to reproduce HAT-P-2's pulsations, suggesting that our understanding of the interactions at play in this system is incomplete.},
doi = {10.3847/2041-8213/836/2/L17},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 836,
place = {United States},
year = {Mon Feb 20 00:00:00 EST 2017},
month = {Mon Feb 20 00:00:00 EST 2017}
}
  • We present observations spanning 355 orbital phases of HAT-P-7 observed by Kepler from 2009 May to 2011 March (Q1-9). We find a shallower secondary eclipse depth than initially announced, consistent with a low optical albedo and detection of nearly exclusively thermal emission, without a reflected light component. We find an approximately 10 ppm perturbation to the average transit light curve near phase -0.02 that we attribute to a temperature decrease on the surface of the star, phased to the orbit of the planet. This cooler spot is consistent with planet-induced gravity darkening, slightly lagging the sub-planet position due to themore » finite response time of the stellar atmosphere. The brightness temperature of HAT-P-7b in the Kepler bandpass is T{sub B} = 2733 {+-} 21 K and the amplitude of the deviation in stellar surface temperature due to gravity darkening is approximately -0.18 K. The detection of the spot is not statistically unequivocal due its small amplitude, though additional Kepler observations should be able to verify the astrophysical nature of the anomaly.« less
  • We present the measured projected obliquity-the sky-projected angle between the stellar spin axis and orbital angular momentum-of the inner planet of the HAT-P-17 multi-planet system. We measure the sky-projected obliquity of the star to be {lambda}=19{sup +14}{sub -16} deg by modeling the Rossiter-McLaughlin effect in Keck/HIRES radial velocities (RVs). The anomalous RV time series shows an asymmetry relative to the midtransit time, ordinarily suggesting a nonzero obliquity-but in this case at least part of the asymmetry may be due to the convective blueshift, increasing the uncertainty in the determination of {lambda}. We employ the semi-analytical approach of Hirano et al.more » that includes the effects of macroturbulence, instrumental broadening, and convective blueshift to accurately model the anomaly in the net RV caused by the planet eclipsing part of the rotating star. Obliquity measurements are an important tool for testing theories of planet formation and migration. To date, the measured obliquities of {approx}50 Jovian planets span the full range, from prograde to retrograde, with planets orbiting cool stars preferentially showing alignment of stellar spins and planetary orbits. Our results are consistent with this pattern emerging from tidal interactions in the convective envelopes of cool stars and close-in planets. In addition, our 1.8 yr of new RVs for this system show that the orbit of the outer planet is more poorly constrained than previously thought, with an orbital period now in the range of 10-36 yr.« less
  • We report the discovery of HAT-P-16b, a transiting extrasolar planet orbiting the V = 10.8 mag F8 dwarf GSC 2792-01700, with a period P = 2.775960 {+-} 0.000003 days, transit epoch T{sub c} = 2455027.59293 {+-} 0.00031 (BJD{sup 10}), and transit duration 0.1276 {+-} 0.0013 days. The host star has a mass of 1.22 {+-} 0.04 M{sub sun}, radius of 1.24 {+-} 0.05 R{sub sun}, effective temperature 6158 {+-} 80 K, and metallicity [Fe/H] = +0.17 {+-} 0.08. The planetary companion has a mass of 4.193 {+-} 0.094 M{sub J} and radius of 1.289 {+-} 0.066 R {sub J}, yieldingmore » a mean density of 2.42 {+-} 0.35 g cm{sup -3}. Comparing these observed characteristics with recent theoretical models, we find that HAT-P-16b is consistent with a 1 Gyr H/He-dominated gas giant planet. HAT-P-16b resides in a sparsely populated region of the mass-radius diagram and has a non-zero eccentricity of e = 0.036 with a significance of 10{sigma}.« less
  • We present the first secondary eclipse and phase curve observations for the highly eccentric hot Jupiter HAT-P-2b in the 3.6, 4.5, 5.8, and 8.0 {mu}m bands of the Spitzer Space Telescope. The 3.6 and 4.5 {mu}m data sets span an entire orbital period of HAT-P-2b (P = 5.6334729 d), making them the longest continuous phase curve observations obtained to date and the first full-orbit observations of a planet with an eccentricity exceeding 0.2. We present an improved non-parametric method for removing the intrapixel sensitivity variations in Spitzer data at 3.6 and 4.5 {mu}m that robustly maps position-dependent flux variations. Wemore » find that the peak in planetary flux occurs at 4.39 {+-} 0.28, 5.84 {+-} 0.39, and 4.68 {+-} 0.37 hr after periapse passage with corresponding maxima in the planet/star flux ratio of 0.1138% {+-} 0.0089%, 0.1162% {+-} 0.0080%, and 0.1888% {+-} 0.0072% in the 3.6, 4.5, and 8.0 {mu}m bands, respectively. Our measured secondary eclipse depths of 0.0996% {+-} 0.0072%, 0.1031% {+-} 0.0061%, 0.071%{sub -0.013%}{sup +0.029,} and 0.1392% {+-} 0.0095% in the 3.6, 4.5, 5.8, and 8.0 {mu}m bands, respectively, indicate that the planet cools significantly from its peak temperature before we measure the dayside flux during secondary eclipse. We compare our measured secondary eclipse depths to the predictions from a one-dimensional radiative transfer model, which suggests the possible presence of a transient day side inversion in HAT-P-2b's atmosphere near periapse. We also derive improved estimates for the system parameters, including its mass, radius, and orbital ephemeris. Our simultaneous fit to the transit, secondary eclipse, and radial velocity data allows us to determine the eccentricity (e = 0.50910 {+-} 0.00048) and argument of periapse ({omega} = 188. Degree-Sign 09 {+-} 0. Degree-Sign 39) of HAT-P-2b's orbit with a greater precision than has been achieved for any other eccentric extrasolar planet. We also find evidence for a long-term linear trend in the radial velocity data. This trend suggests the presence of another substellar companion in the HAT-P-2 system, which could have caused HAT-P-2b to migrate inward to its present-day orbit via the Kozai mechanism.« less
  • We report the discovery by the HATNet survey of three new transiting extrasolar planets orbiting moderately bright (V = 13.2, 12.8, and 11.9) stars. The planets have orbital periods of 4.3012, 3.1290, and 4.4631 days, masses of 0.35, 0.89, and 0.49 M {sub J}, and radii of 1.24, 1.43, and 1.28 R {sub J}. The stellar hosts have masses of 0.94, 1.26, and 1.28 M {sub ☉}. Each system shows significant systematic variations in its residual radial velocities, indicating the possible presence of additional components. Based on its Bayesian evidence, the preferred model for HAT-P-44 consists of two planets, includingmore » the transiting component, with the outer planet having a period of 872 days, eccentricity of 0.494 ± 0.081, and a minimum mass of 4.0 M {sub J}. Due to aliasing we cannot rule out alternative solutions for the outer planet having a period of 220 days or 438 days. For HAT-P-45, at present there is not enough data to justify the additional free parameters included in a multi-planet model; in this case a single-planet solution is preferred, but the required jitter of 22.5 ± 6.3 m s{sup –1} is relatively high for a star of this type. For HAT-P-46 the preferred solution includes a second planet having a period of 78 days and a minimum mass of 2.0 M {sub J}, however the preference for this model over a single-planet model is not very strong. While substantial uncertainties remain as to the presence and/or properties of the outer planetary companions in these systems, the inner transiting planets are well characterized with measured properties that are fairly robust against changes in the assumed models for the outer planets. Continued radial velocity monitoring is necessary to fully characterize these three planetary systems, the properties of which may have important implications for understanding the formation of hot Jupiters.« less