Penev, Kaloyan

Permanent URI for this collectionhttps://hdl.handle.net/10735.1/6247

Kaloyan Penev joined the UTD faculty as an Assistant Professor of Physics in 2017. His research interests include:

Extrasolar planet detection and orbital dynamics
Searching for transiting extrasolar planets using small robotic telescopes
High precision photometry from space and from the ground
Orbital dynamics of extrasolar planetary systems
Astrophysical probes of tidal dissipation in giant planets and low mass stars

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Kelt-19Ab: A P ~ 4.6-day Hot Jupiter Transiting a Likely Am Star with a Distant Stellar Companion
(IOP Publishing Ltd, 2018-11-05) Siverd, Robert J.; Collins, Karen A.; Zhou, George; Quinn, Samuel N.; Gaudi, B. Scott; Stassun, Keivan G.; Johnson, Marshall C.; Penev, Kaloyan; Penev, Kaloyan
We present the discovery of the giant planet KELT-19Ab, which transits the moderately bright (V similar to 9.9) A8V star TYC 764-1494-1 with an orbital period of 4.61 days. We confirm the planetary nature of the companion via a combination of. radial velocities, which limit the mass to less than or similar to 4.1 M-J (3 sigma), and a clear Doppler tomography signal, which indicates a retrograde projected spin-orbit misalignment of lambda = -179.7(-3.7)(+3.8) degrees. Global modeling indicates that the T-eff=7500. 110 K host star has M-star = 1.62(-0.20)(+0.25) M-star and R-star = 1.83 +/- 0.10 R-circle dot. The planet has a radius of R-P = 1.91 +/- 0.11 R-J and receives a stellar insolation flux of similar to 3.2 x 10(9) erg s(-1) cm(-2), leading to an inferred equilibrium temperature of T-eq similar to 1935 K assuming zero albedo and complete heat redistribution. With a v sin I-* = 84.8 +/- 2.0 km s(-1), the host. is relatively slowly rotating compared to other stars with similar effective temperatures, and it appears to be enhanced in metallic elements but deficient in calcium, suggesting that it is likely an Am star. KELT-19A would be the first detection of an Am host of a transiting planet of which we are aware. Adaptive optics observations of the system reveal the existence of a companion with late-G9V/early-K1V spectral type at a projected separation of approximate to 160 au. Radial velocity measurements indicate that this companion is bound. Most Am stars are known to have stellar companions, which are often invoked to explain the relatively slow rotation of the primary. In this case, the stellar companion is unlikely to have caused the tidal braking of the primary. However, it may have emplaced the transiting planetary companion via the Kozai-Lidov mechanism.
Hats-70b: A 13 MJ Brown Dwarf Transiting an A Star
(IOP Publishing Ltd, 2019-01-02) Zhou, G.; Bakos, G. A.; Bayliss, D.; Bento, J.; Bhatti, W.; Brahm, R.; Csubry, Z.; Espinoza, N.; Hartman, J. D.; Henning, T.; Jordan, A.; Mancini, L.; Penev, Kaloyan; Rabus, M.; Sarkis, P.; Suc, V.; de Val-Borro, M.; Rodriguez, J. E.; Osip, D.; Kedziora-Chudczer, L.; Bailey, J.; Tinney, C. G.; Durkan, S.; Lazar, J.; Papp, I.; Sari, P.; 0000-0003-4464-1371 (Penev, K); Penev, Kaloyan
We report the discovery of HATS-70b, a transiting brown dwarf at the deuterium burning limit. HATS-70b has a mass of M_{p} = 12.9{{-1.6}^{+1.8} M_{Jup} and a radius of R_{p} = 1.384_{{-0.074} {+0.079}} R_{Jup}, residing in a close-in orbit with a period of 1.89 days. The host star is a M⁎ = 1.78 ± 0.12 M_⊙ A star rotating at v sin I⁎ = 40.61{_{-0.35}}^{+0.32}} km s⁻¹ , enabling us to characterize the spectroscopic transit of the brown dwarf via Doppler tomography. We find that HATS-70b, like other massive planets and brown dwarfs previously sampled, orbits in a low projected-obliquity orbit with λ = {_{8.9}^{5.6°}}. The low obliquities of these systems is surprising given all brown dwarf and massive planets with obliquities measured orbit stars hotter than the Kraft break. This trend is tentatively inconsistent with dynamically chaotic migration for systems with massive companions, though the stronger tidal influence of these companions makes it difficult to draw conclusions on the primordial obliquity distribution of this population. We also introduce a modeling scheme for planets around rapidly rotating stars, accounting for the influence of gravity darkening on the derived stellar and planetary parameters.
KELT-22Ab: A Massive, Short-Period Hot Jupiter Transiting a Near-Solar Twin
(IOP Publishing Ltd, 2019-01-21) Labadie-Bartz, Jonathan; Rodriguez, Joseph E.; Stassun, Keivan G.; Ciardi, David R.; Penev, Kaloyan; Johnson, Marshall C.; Gaudi, B. Scott; 0000-0003-4464-1371 (Penev, K); Penev, Kaloyan
We present the discovery of KELT-22Ab, a hot Jupiter from the KELT-South survey. KELT-22Ab transits the moderately bright (V ~ 11.1) Sun-like G2V star TYC 7518-468-1. The planet has an orbital period of P = 1.3866529 ± 0.0000027 days, a radius of R_{P} = 1.285{_{-0.071}^{+0.12}} R_{J}, and a relatively large mass of M_{P} = 3.47{_{-0.14}^{+0.15}}, M_{J}. The star has R_{⋆} = 1.099{_{-0.046}^{0.079}} R_{⊙}, M_{⋆} = 1.092{_{-0.041}^{+0.045}} M_{⊙}, T_{eff} = 5767{_{-49}^{+50}} K, log g_{⋆} = 4.393{_{-0.060}^{+0.039}} (cgs), and [m/H] = +0.259{_{-0.083}^{+0.085}}; thus other than its slightly super-solar metallicity, it appears to be a near-solar twin. Surprisingly, KELT-22A exhibits kinematics and a Galactic orbit that are somewhat atypical for thin-disk stars. Nevertheless, the star is rotating rapidly for its estimated age, and shows evidence of chromospheric activity. Imaging reveals a slightly fainter companion to KELT-22A that is likely bound, with a projected separation of 6 '' (similar to 1400 au). In addition to the orbital motion caused by the transiting planet, we detect a possible linear trend in the radial velocity of KELT-22A, suggesting the presence of another relatively nearby body that is perhaps non-stellar. KELT-22Ab is highly irradiated (as a consequence of the small semimajor axis of a/R_{⋆}, and is mildly inflated. At such small separations, tidal forces become significant. The configuration of this system is optimal for measuring the rate of tidal dissipation within the host star. Our models predict that, due to tidal forces, the semimajor axis is decreasing rapidly, and KELT-22Ab is predicted to spiral into the star within the next Gyr.
HATS-60b-HATS-69b: 10 Transiting Planets from HATSouth
(IOP Publishing Ltd, 2019-02) Hartman, J. D.; Bakos, G. A.; Bayliss, D.; Bento, J.; Bhatti, W.; Brahm, R.; Csubry, Z.; Espinoza, N.; Penev, Kaloyan; Penev, Kaloyan
We report the discovery of 10 transiting extrasolar planets by the HATSouth survey. The planets range in mass from the super-Neptune HATS-62b, with Mₚ < 0.179 Mⱼ, to the super-Jupiter HATS-66b, with Mₚ = 5.33 Mⱼ, and in size from the Saturn HATS-69b, with Rₚ = 0.94 Rⱼ, to the inflated Jupiter HATS-67b, with Rₚ = 1.69 Rⱼ. The planets have orbital periods between 1.6092 days (HATS-67b) and 7.8180 days (HATS-61b). The hosts are dwarf stars with masses ranging from 0.89 M⊙(HATS-69) to 1.56 M⊙ (HATS-64) and have apparent magnitudes between V = 12.276 ± 0.020 mag (HATS-68) and V = 14.095 ± 0.030 mag (HATS-66). The super-Neptune HATS-62b is the least massive planet discovered to date with a radius larger than Jupiter. Based largely on the Gaia DR2 distances and broadband photometry, we identify three systems (HATS-62, HATS-64, and HATS-65) as having possible unresolved binary star companions. We discuss in detail our methods for incorporating the Gaia DR2 observations into our modeling of the system parameters and into our blend analysis procedures.
An Eccentric Massive Jupiter Orbiting a Subgiant on a 9.5-day Period Discovered in the Transiting Exoplanet Survey Satellite Full Frame Images
(Institute of Physics Publishing, 2019-05) Rodriguez, J. E.; Quinn, S. N.; Huang, C. X.; Vanderburg, A.; Penev, Kaloyan; Brahm, R.; Jordán, A.; 0000-0003-4464-1371 (Penev, K); Penev, Kaloyan
We report the discovery of TOI-172 b from the Transiting Exoplanet Survey Satellite (TESS) mission, a massive hot Jupiter transiting a slightly evolved G star with a 9.48-day orbital period. This is the first planet to be confirmed from analysis of only the TESS full frame images, because the host star was not chosen as a two-minute cadence target. From a global analysis of the TESS photometry and follow-up observations carried out by the TESS Follow-up Observing Program Working Group, TOI-172 (TIC 29857954) is a slightly evolved star with an effective temperature of T_{eff} = 5645 ± 50 K, a mass of M_{∗} = 1.128_{-0.061} ^{+0.065} M ⊙, radius of R_{∗} = 1.777_{-0.044} ^{+0.047} R ⊙, a surface gravity of log g_{∗} = 3.993 _{-0.028} ^{+0.027}, and an age of 7.4 _{-1.5} ^{+1.6}. Its planetary companion (TOI-172 b) has a radius of R _{P} = 0.965 _{-0.029} ^{+0.032} R_{J}, a mass of M _{P} = 5.42 _{-0.20} ^{+0.22} M _{J}, and is on an eccentric orbit (e = 0.3806 _{-0.0090} ^{+0.0093} ). TOI-172 b is one of the few known massive giant planets on a highly eccentric short-period orbit. Future study of the atmosphere of this planet and its system architecture offer opportunities to understand the formation and evolution of similar systems. © 2019. The American Astronomical Society. All rights reserved..
HAT-TR-318-007: A Double-Lined M Dwarf Binary with Total Secondary Eclipses Discovered by HATNet and Observed by K2
(Institute of Physics Publishing) Hartman, J. D.; Quinn, S. N.; Bakos, G. A.; Torres, G.; Kovács, G.; Latham, D. W.; Noyes, R. W.; Shporer, A.; Fulton, B. J.; Esquerdo, G. A.; Everett, M. E.; Penev, Kaloyan; Bhatti, W.; Csubry, Z.; 0000-0003-4464-1371 (Penev, K); Penev, Kaloyan
We report the discovery by the HATNet survey of HAT-TR-318-007, a P = 3.34395390 ± 0.00000020 day period detached double-lined M dwarf binary with total secondary eclipses. We combine radial velocity (RV) measurements from TRES/FLWO 1.5 m and time-series photometry from HATNet, FLWO 1.2 m, BOS 0.8 m, and NASA K2 Campaign 5, to determine the masses and radii of the component stars: MA = 0.448 ± 0.011M⊙ N, MB 0.2721-0.0042 +0.0041 M⊙ N, RA 0.4548-0.0036 +0.0035R⊙ N, and RB 0.2913-0.0024 +0.0023R⊙ N. We obtained a FIRE/Magellan near-infrared spectrum of the primary star during a total secondary eclipse, and we use this to obtain disentangled spectra of both components. We determine spectral types of STA = M3.71 ± 0.69 and STB = M5.01 ± 0.73 and effective temperatures of Teff,A = 3190 ± 110 K and Teff,B = 3100 ± 110 K for the primary and secondary star, respectively. We also measure a metallicity of Fe/H]= +0.298 ± 0.080 for the system. We find that the system has a small, but significant, nonzero eccentricity of 0.0136 ± 0.0026. The K2 light curve shows a coherent variation at a period of 3.41315-0.00032 +0.00030 days, which is slightly longer than the orbital period, and which we demonstrate comes from the primary star. We interpret this as the rotation period of the primary. We perform a quantitative comparison between the Dartmouth stellar evolution models and the seven systems, including HATTR-318-007, that contain M dwarfs with 0.2M⊙ N < M < 0.5M⊙ N, have metallicity measurements, and have masses and radii determined to better than 5% precision. Discrepancies between the predicted and observed masses and radii are found for three of the systems. © 2018. The American Astronomical Society. All rights reserved.
HATS-39b, HATS-40b, HATS-41b, and HATS-42b: Three Inflated Hot Jupiters and a Super-Jupiter Transiting F Stars
(Oxford Univ Press) Bento, J.; Hartman, J. D.; Bakos, G. A.; Bhatti, W.; Csubry, Z.; Penev, Kaloyan; Bayliss, D.; de Val-Borro, M.; Zhou, G.; Brahm, R.; Espinoza, N.; Rabus, M.; Jordan, A.; Suc, V.; Ciceri, S.; Sarkis, P.; Henning, T.; Mancini, L.; Tinney, C. G.; Wright, D. J.; Durkan, S.; Tan, T. G.; Lazar, J.; Papp, I.; Sari, P.; 0000-0003-4464-1371 (Penev, K); Penev, Kaloyan
We report the discovery of four transiting hot Jupiters from the HATSouth survey: HATS39b, HATS-40b, HATS-41b, and HATS-42b. These discoveries add to the growing number of transiting planets orbiting moderately bright (12.5 ≲ V ≲ 13.7) F dwarf stars on short (2-5 d) periods. The planets have similar radii, ranging from 1.33{_{0.20}^{+0.29}} R_J for HATS-41b to 1.58{_{-0.12} ^{+0.16}} R_J for HATS-40b. Their masses and bulk densities, however, span more than an order of magnitude. HATS-39b has a mass of 0.63 ± 0.13M(J), and an inflated radius of 1.57 ± 0.12 R-J, making it a good target for future transmission spectroscopic studies. HATS41b is a very massive 9.7 ± 1.6M_J planet and one of only a few hot Jupiters found to date with a mass over 5 M_J. This planet orbits the highest metallicity star ([Fe/H] = 0.470 ± 0.010) known to host a transiting planet and is also likely on an eccentric orbit. The high mass, coupled with a relatively young age (1.34{_{-0.51} ^{+0.31}} Gyr) for the host star, is a factor that may explain why this planet's orbit has not yet circularized.

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