Kepler-91b

Kepler-91b is a giant planet orbiting Kepler-91, a star slightly more massive than the Sun. Kepler-91 has left the main sequence and is now a red giant branch star.

Kepler-91b
Discovery
Discovery date2013
Transit (Kepler Mission)
Orbital characteristics
0.072+0.007
−0.002 AU
6.24658 d
Inclination68.5+1.6
−1
StarKepler-91
Physical characteristics
Mean radius
1.322+0.094
−0.086 RJ
Mass0.88+0.33
−0.17 MJ
Mean density
0.44 g/cm3 (0.016 lb/cu in)
Albedo0.39 [1]
Temperature2132 K

    Discovery and further confirmation

    Kepler-91b was detected by analyzing the data of Kepler spacecraft where a transit-like signal was found. Initially thought to be a false positive due to light curve variations by a self-luminous object, it was later revealed that due to low density of Kepler-91's shape is distorted to slightly ellipsoidal shape due to gravitational effects of the planet. Ellipsoidal light variations caused by Kepler-91b constitute more than the third of light variations compared to transit depth. Ellipsoidal light variations also allowed to determine the planet's mass. It was also found that Kepler-91b reflects some of the starlight from its star.[2]

    Further analysis managed to question the planetary nature of the object, suspecting that it is a self-luminous object.[3] However, the planetary nature was eventually confirmed again through both the radial velocity technique[4] and re-analysis of the light curve modulations.[5]

    Characteristics

    Kepler-91b is about 14% less massive than Jupiter while being more than 35% larger, making it less than half of the density of water. Kepler-91b orbits around the host star in about 6.25 days. Despite being one of the least edge-on orbits relative to Earth with inclination being about 68.5 degrees, transit was detected due to low semi-major axis to host star radius ratio.

    Kepler-91b is expected to be engulfed by the parent star within about 55 million years.[2][1]

    Possible trojan companion

    The possibility of a trojan planet to Kepler-91b was suggested due to the presence of a small dim in the phase-folded light curve at phase 0.68.[2] This was subsequently studied but the conclusion was that the transit-signal was a false-positive.[6]

    References
    1. Esteves, Lisa J.; De Mooij, Ernst J. W.; Jayawardhana, Ray (2014). "Changing Phases of Alien Worlds: Probing Atmospheres of Kepler Planets with High-Precision Photometry". The Astrophysical Journal. 804 (2): 150. arXiv:1407.2245. Bibcode:2015ApJ...804..150E. doi:10.1088/0004-637X/804/2/150. S2CID 117798959.
    2. Lillo-Box, J.; Barrado, D.; Moya, A.; Montesinos, B.; Montalbán, J.; Bayo, A.; Barbieri, M.; Régulo, C.; Mancini, L.; Bouy, H.; Henning, T. (2013). "Kepler-91b: A planet at the end of its life. Planet and giant host star properties via light-curve variations". Astronomy & Astrophysics. 562: A109. arXiv:1312.3943. Bibcode:2014A&A...562A.109L. doi:10.1051/0004-6361/201322001. S2CID 118486056.
    3. Sliski, David H.; Kipping, David M. (2014). "A High False Positive Rate for Kepler Planetary Candidates of Giant Stars using Asterodensity Profiling". The Astrophysical Journal. 788 (2): 148. arXiv:1401.1207. Bibcode:2014ApJ...788..148S. doi:10.1088/0004-637X/788/2/148. S2CID 118665291.
    4. Lillo-Box, J.; Barrado, D.; Henning, Th.; Mancini, L.; Ciceri, S.; Figueira, P.; Santos, N. C.; Aceituno, J.; Sánchez, S. (August 2014). "Radial velocity confirmation of Kepler-91 b". Astronomy & Astrophysics. 568: L1. arXiv:1408.1528. doi:10.1051/0004-6361/201424587. ISSN 0004-6361. S2CID 118424631.
    5. Barclay, Thomas; Endl, Michael; Huber, Daniel; Foreman-Mackey, Daniel; Cochran, William D.; MacQueen, Phillip J.; Rowe, Jason F.; Quintana, Elisa V. (2015). "Radial Velocity Observations and Light Curve Noise Modeling Confirm that Kepler-91b is a Giant Planet Orbiting a Giant Star". The Astrophysical Journal. 800 (1): 46. arXiv:1408.3149. Bibcode:2015ApJ...800...46B. doi:10.1088/0004-637X/800/1/46. ISSN 0004-637X. S2CID 118528237.
    6. Placek, Ben; Knuth, Kevin H.; Angerhausen, Daniel; Jenkins, Jon M. (2015). "Characterization of Kepler-91b and the Investigation of a Potential Trojan Companion Using EXONEST". The Astrophysical Journal. 814 (2): 147. arXiv:1511.01068. Bibcode:2015ApJ...814..147P. doi:10.1088/0004-637X/814/2/147. S2CID 118366565.
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