Browsing by Author "Sedaghati, Elyar"

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    HATS-38 b and WASP-139 b Join a Growing Group of Hot Neptunes on Polar Orbits
    (2024) Espinoza-Retamal, Juan I.; Stefansson, Gudmundur; Petrovich, Cristobal; Brahm, Rafael; Jordan, Andres; Sedaghati, Elyar; Lucero, Jennifer P.; Pinto, Marcelo Tala; Munoz, Diego J.; Boyle, Gavin; Leiva, Rodrigo; Suc, Vincent
    We constrain the sky-projected obliquities of two low-density hot Neptune planets, HATS-38 b and WASP-139 b, orbiting nearby G and K stars using Rossiter-McLaughlin (RM) observations with VLT/ESPRESSO, yielding lambda=-108(-16)(+11) deg and -85.6(-4.2)(+7.7) deg, respectively. To model the RM effect, we use a new publicly available code, ironman, which is capable of jointly fitting transit photometry, Keplerian radial velocities, and RM effects. WASP-139 b has a residual eccentricity e=0.103(-0.041)(+0.050) while HATS-38 b has an eccentricity of e=0.112(-0.070)(+0.072), which is compatible with a circular orbit given our data. Using the obliquity constraints, we show that they join a growing group of hot and low-density Neptunes on polar orbits. We use long-term radial velocities to rule out companions with masses similar to 0.3-50 M-J within similar to 10 au. We show that the orbital architectures of the two Neptunes can be explained with high-eccentricity migration from greater than or similar to 2 au driven by an unseen distant companion. If HATS-38b has no residual eccentricity, its polar and circular orbit can also be consistent with a primordial misalignment. Finally, we performed a hierarchical Bayesian modeling of the true obliquity distribution of Neptunes and found suggestive evidence for a higher preponderance of polar orbits of hot Neptunes compared to Jupiters. However, we note that the exact distribution is sensitive to the choice of priors, highlighting the need for additional obliquity measurements of Neptunes to robustly compare the hot Neptune obliquity distribution to Jupiters.
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    HD 2685 b: a hot Jupiter orbiting an early F-type star detected by TESS
    (2019) Jones, Matias, I; Brahm, Rafael; Espinoza, Nestor; Wang, Songhu; Shporer, Avi; Henning, Thomas; Jordan, Andres; Sarkis, Paula; Paredes, Leonardo A.; Hodari-Sadiki, James; Henrys, Todd; Cruz, Bryndis; Nielsen, Louise D.; Bouchy, Francois; Pepe, Francesco; Segransan, Damien; Turner, Oliver; Udry, Stephane; Marmier, Maxime; Lovis, Christophe; Bakos, Gaspar; Osip, David; Suc, Vincent; Ziegler, Carl; Tokovinin, Andrei; Law, Nick M.; Mann, Andrew W.; Relles, Howard; Collins, Karen A.; Bayliss, Daniel; Sedaghati, Elyar; Latham, David W.; Seager, Sara; Winn, Joshua N.; Jenkins, Jon M.; Smith, Jeffrey C.; Davies, Misty; Tenenbaum, Peter; Dittmann, Jason; Vanderburg, Andrew; Christiansen, Jessie L.; Haworth, Kari; Doty, John; Furesz, Gabor; Laughlin, Greg; Matthews, Elisabeth; Crossfield, Ian; Howell, Steve; Ciardi, David; Gonzales, Erica; Matson, Rachel; Beichman, Charles; Schlieder, Joshua
    We report on the confirmation of a transiting giant planet around the relatively hot (T-eff = 6801 +/- 76 K) star HD 2685, whose transit signal was detected in Sector 1 data of NASA's TESS mission. We confirmed the planetary nature of the transit signal using Doppler velocimetric measurements with CHIRON, CORALIE, and FEROS, as well as using photometric data obtained with the Chilean-Hungarian Automated Telescope and the Las Cumbres Observatory. From the joint analysis of photometry and radial velocities, we derived the following parameters for HD 2685 b: P =4.12688(-0.00004)(+0.00005) days, e =0.091(-0.047)(+0.039), Mp = 1.17 +/- 0.12 M-J, and R-p =1.44 +/- 0.05 R-J. This system is a typical example of an inflated transiting hot Jupiter in a low-eccentricity orbit. Based on the apparent visual magnitude (V = 9.6 mag) of the host star, this is one of the brightest known stars hosting a transiting hot Jupiter, and it is a good example of the upcoming systems that will be detected by TESS during the two-year primary mission. This is also an excellent target for future ground- and space-based atmospheric characterization as well as a good candidate for measuring the projected spin-orbit misalignment angle through the Rossiter-McLaughlin effect.
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    Orbital Alignment of the Eccentric Warm Jupiter TOI-677 b
    (2023) Sedaghati, Elyar; Jordan, Andres; Brahm, Rafael; Munoz, Diego J.; Petrovich, Cristobal; Hobson, Melissa J.
    Warm Jupiters lay out an excellent laboratory for testing models of planet formation and migration. Their separation from the host star makes tidal reprocessing of their orbits ineffective, which preserves the orbital architectures that result from the planet-forming process. Among the measurable properties, the orbital inclination with respect to the stellar rotational axis, stands out as a crucial diagnostic for understanding the migration mechanisms behind the origin of close-in planets. Observational limitations have made the procurement of spin-orbit measurements heavily biased toward hot Jupiter systems. In recent years, however, high-precision spectroscopy has begun to provide obliquity measurements for planets well into the warm Jupiter regime. In this study, we present Rossiter-McLaughlin (RM) measurements of the projected obliquity angle for the warm Jupiter TOI-677 b using ESPRESSO at the VLT. TOI-677 b exhibits an extreme degree of alignment (lambda = 0.3 +/- 1.3 deg), which is particularly puzzling given its significant eccentricity (e approximate to 0.45). TOI-677 b thus joins a growing class of close-in giants that exhibit large eccentricities and low spin-orbit angles, which is a configuration not predicted by existing models. We also present the detection of a candidate outer brown dwarf companion on an eccentric, wide orbit (e approximate to 0.4 and P approximate to 13 yr). Using simple estimates, we show that this companion is unlikely to be the cause of the unusual orbit of TOI-677 b. Therefore, it is essential that future efforts prioritize the acquisition of RM measurements for warm Jupiters.
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    The Aligned Orbit of the Eccentric Proto Hot Jupiter TOI-3362b
    (2023) Espinoza Retamal, Juan; Brahm, Rafael; Petrovich, Cristobal; Jordán, Andrés; Stefánsson, Guðmundur; Sedaghati, Elyar; Hobson, Melissa J.; Muñoz, Diego J.; Boyle, Gavin; Leiva, Rodrigo; Suc, Vincent
    High-eccentricity tidal migration predicts the existence of highly eccentric proto-hot Jupiters on the "tidal circularization track," meaning that they might eventually become hot Jupiters, but that their migratory journey remains incomplete. Having experienced moderate amounts of the tidal reprocessing of their orbital elements, proto-hot Jupiters systems can be powerful test-beds for the underlying mechanisms of eccentricity growth. Notably, they may be used for discriminating between variants of high-eccentricity migration, each predicting a distinct evolution of misalignment between the star and the planet's orbit. We constrain the spin-orbit misalignment of the proto-hot Jupiter TOI-3362b with high-precision radial velocity observations using ESPRESSO at VLT. The observations reveal a sky-projected obliquity $\lambda = 1.2_{-2.7}^{+2.8}$ deg and constrain the orbital eccentricity to $e=0.720 \pm 0.016$, making it one of the most eccentric gas giants for which the obliquity has been measured. The large eccentricity and the striking orbit alignment of the planet suggest that ongoing coplanar high-eccentricity migration driven by a distant companion is a likely explanation for the system's architecture. This distant companion would need to reside beyond 5 au at 95% confidence to be compatible with the available radial velocity observations....