| 61. |
- Hatzes, A., et al.
(author)
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A Radial Velocity Study of the Planetary System of π Mensae: Improved Planet Parameters for pi Mensae c and a Third Planet on a 125 Day Orbit
- 2022
-
In: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 163:5
-
Journal article (peer-reviewed)abstract
- π Men hosts a transiting planet detected by the Transiting Exoplanet Survey Satellite space mission and an outer planet in a 5.7 yr orbit discovered by radial velocity (RV) surveys. We studied this system using new RV measurements taken with the HARPS spectrograph on ESO's 3.6 m telescope, as well as archival data. We constrain the stellar RV semiamplitude due to the transiting planet, π Men c, as K c = 1.21 ± 0.12 m s-1, resulting in a planet mass of M c = 3.63 ± 0.38 M. A planet radius of R c = 2.145 ± 0.015 R yields a bulk density of ρ c = 2.03 ± 0.22 g cm-3. The precisely determined density of this planet and the brightness of the host star make π Men c an excellent laboratory for internal structure and atmospheric characterization studies. Our HARPS RV measurements also reveal compelling evidence for a third body, π Men d, with a minimum mass M d sin i d = 13.38 ± 1.35 M orbiting with a period of P orb,d = 125 days on an eccentric orbit (e d = 0.22). A simple dynamical analysis indicates that the orbit of π Men d is stable on timescales of at least 20 Myr. Given the mutual inclination between the outer gaseous giant and the inner rocky planet and the presence of a third body at 125 days, π Men is an important planetary system for dynamical and formation studies.
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| 62. |
- Henning, Th., et al.
(author)
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HATS-50b through HATS-53b : Four Transiting Hot Jupiters Orbiting G-type Stars Discovered by the HATSouth Survey
- 2018
-
In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 155:2
-
Journal article (peer-reviewed)abstract
- We report the discovery of four close-in transiting exoplanets (HATS-50b through HATS-53b), discovered using the HATSouth three-continent network of homogeneous and automated telescopes. These new exoplanets belong to the class of hot Jupiters and orbit G-type dwarf stars, with brightness in the range V = 12.5-14.0 mag. While HATS-53 has many physical characteristics similar to the Sun, the other three stars appear to be metal-rich ([Fe/H]= 0.2-0.3), larger, and more massive. Three of the new exoplanets, namely HATS-50b, HATS-51b, and HATS-53b, have low density (HATS-50b: 0.39 +/- 0.10 M-J, 1.130 +/- 0.075 R-J; HATS-51b: 0.768 +/- 0.045 M-J, 1.41 +/- 0.19 R-J; HATS-53b: 0.595 +/- 0.089 M-J, 1.340 +/- 0.056 R-J) and similar orbital periods (3.8297 days, 3.3489 days, 3.8538 days, respectively). Instead, HATS-52b is more dense (mass 2.24. +/- 0.15 M-J and radius 1.382 +/- 0.086 R-J) and has a shorter orbital period (1.3667 days). It also receives an intensive radiation from its parent star and, consequently, presents a high equilibrium temperature (T-eq = 1834 +/- 73 K). HATS-50 shows a marginal additional transit feature consistent with an ultra-short-period hot super Neptune (upper mass limit 0.16 M-J), which will be able to be confirmed with TESS photometry.
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| 63. |
- Hirano, T., et al.
(author)
-
An Earth-sized Planet around an M5 Dwarf Star at 22 pc
- 2023
-
In: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 165:3
-
Journal article (peer-reviewed)abstract
- We report on the discovery of an Earth-sized transiting planet (R p = 1.015 ± 0.051 R ⊕) in a P = 4.02 day orbit around K2-415 (EPIC 211414619), an M5V star at 22 pc. The planet candidate was first identified by analyzing the light-curve data obtained by the K2 mission, and it is here shown to exist in the most recent data from TESS. Combining the light curves with the data secured by our follow-up observations, including high-resolution imaging and near-infrared spectroscopy with IRD, we rule out false-positive scenarios, finding a low false-positive probability of 2 × 10−4. Based on IRD’s radial velocities of K2-415, which were sparsely taken over three years, we obtain a planet mass of 3.0 ± 2.7 M ⊕ (M p < 7.5 M ⊕ at 95% confidence) for K2-415b. Being one of the lowest-mass stars (≈0.16 M ⊙) known to host an Earth-sized transiting planet, K2-415 will be an interesting target for further follow-up observations, including additional radial velocity monitoring and transit spectroscopy.
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| 64. |
- Hirano, Teruyuki, et al.
(author)
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Exoplanets around Low-mass Stars Unveiled by K2
- 2018
-
In: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 155:3, s. 127-
-
Journal article (peer-reviewed)abstract
- We present the detection and follow-up observations of planetary candidates around low-mass stars observed by the K2 mission. Based on light-curve analysis, adaptive-optics imaging, and optical spectroscopy at low and high resolution (including radial velocity measurements), we validate 16 planets around 12 low-mass stars observed during K2 campaigns 5–10. Among the 16 planets, 12 are newly validated, with orbital periods ranging from 0.96 to 33 days. For one of the planets (K2-151b), we present ground-based transit photometry, allowing us to refine the ephemerides. Combining our K2 M-dwarf planets together with the validated or confirmed planets found previously, we investigate the dependence of planet radius R p on stellar insolation and metallicity [Fe/H]. We confirm that for periods P ≲ 2 days, planets with a radius Rp≳ 2 R⊕ are less common than planets with a radius between 1–2 R⊕. We also see a hint of the “radius valley” between 1.5 and 2 R⊕, which has been seen for close-in planets around FGK stars. These features in the radius/period distribution could be attributed to photoevaporation of planetary envelopes by high-energy photons from the host star, as they have for FGK stars. For the M dwarfs, though, the features are not as well defined, and we cannot rule out other explanations such as atmospheric loss from internal planetary heat sources or truncation of the protoplanetary disk. There also appears to be a relation between planet size and metallicity: the few planets larger than about 3 R⊕ are found around the most metal-rich M dwarfs.
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| 65. |
- Hirano, T., et al.
(author)
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K2-155: A Bright Metal-poor M Dwarf with Three Transiting Super-Earths
- 2018
-
In: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 155:3
-
Journal article (peer-reviewed)abstract
- We report on the discovery of three transiting super-Earths around K2-155 (EPIC 210897587), a relatively bright early M dwarf (V = 12.81 mag) observed during Campaign 13 of the NASA K2 mission. To characterize the system and validate the planet candidates, we conducted speckle imaging and high-dispersion optical spectroscopy, including radial velocity measurements. Based on the K2 light curve and the spectroscopic characterization of the host star, the planet sizes and orbital periods are 1.55 -0.17 +0.20 R ⊕ and 6.34365 ±0.00028 days for the inner planet; 1.95 -0.22 +0.27 R ⊕ and 13.85402 ±0.00088 days for the middle planet; and 1.64 -0.17 +0.18 R ⊕ and 40.6835 ±0.0031 days for the outer planet. The outer planet (K2-155d) is near the habitable zone, with an insolation 1.67 ±0.38 times that of the Earth. The planet's radius falls within the range between that of smaller rocky planets and larger gas-rich planets. To assess the habitability of this planet, we present a series of three-dimensional global climate simulations, assuming that K2-155d is tidally locked and has an Earth-like composition and atmosphere. We find that the planet can maintain a moderate surface temperature if the insolation proves to be smaller than ∼1.5 times that of the Earth. Doppler mass measurements, transit spectroscopy, and other follow-up observations should be rewarding, as K2-155 is one of the optically brightest M dwarfs known to harbor transiting planets.
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| 66. |
- Hirao, Yuki, et al.
(author)
-
OGLE-2017-BLG-0406 : Spitzer Microlens Parallax Reveals Saturn-mass Planet Orbiting M-dwarf Host in the Inner Galactic Disk
- 2020
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 160:2
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Journal article (peer-reviewed)abstract
- We report the discovery and analysis of the planetary microlensing event OGLE-2017-BLG-0406, which was observed both from the ground and by the Spitzer satellite in a solar orbit. At high magnification, the anomaly in the light curve was densely observed by ground-based-survey and follow-up groups, and it was found to be explained by a planetary lens with a planet/host mass ratio of q = 7.0 x 10(-4) from the light-curve modeling. The ground-only and Spitzer-only data each provide very strong one-dimensional (1D) constraints on the 2D microlens parallax vector pi(E). When combined, these yield a precise measurement of pi(E) and of the masses of the host M-host = 0.56 +/- 0.07 M-circle dot and planet M-planet = 0.41 +/- 0.05 M-Jup. The system lies at a distance D-L = 5.2 +/- 0.5 kpc from the Sun toward the Galactic bulge, and the host is more likely to be a disk population star according to the kinematics of the lens. The projected separation of the planet from the host is a(perpendicular to) = 3.5 +/- 0.3 au (i.e., just over twice the snow line). The Galactic-disk kinematics are established in part from a precise measurement of the source proper motion based on OGLE-IV data. By contrast, the Gaia proper-motion measurement of the source suffers from a catastrophic 10 sigma error.
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| 67. |
- Hoard, D. W., et al.
(author)
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Multiwavelength Ground and Space Observations of the Variable White Dwarf BOKS 53856 : Nonuniform Metal Absorption in Dark Spots
- 2018
-
In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 156:3
-
Journal article (peer-reviewed)abstract
- We analyze extensive ground- and space-based ultraviolet-infrared observations of the variable white dwarf BOKS 53856. Photometry and spectroscopy were obtained from the Hubble Space Telescope, Spitzer Space Telescope, Kepler and Swift satellites, Palomar Observatory, and Kitt Peak National Observatory. Time series data spanning the entire four-year Kepler mission are used to refine the photometric rotation period of the white dwarf to 0.2557292(9) days. The associated periodic variability, with full (minimum to maximum) amplitudes of approximate to 5% and approximate to 10% in the optical and ultraviolet, respectively, is consistent with the presence of several dark spots on the white dwarf surface. A fit to the observed ultraviolet-infrared spectral energy distribution of BOKS 53856 using a grid of non-LTE synthetic spectra gives best values of effective temperature, T-WD = 31,056(19) K, surface gravity, log g = 7.913(5), mass, M-WD = 0.603(2) M-circle dot, radius, R-WD = 0.0142(4) R-circle dot, reddening, Eb-v = 0.0533(1), and distance, d = 277(10) pc. The Hubble ultraviolet spectrum does not show a detectable signature of accreted metals, and the Spitzer infrared photometry does not reveal an excess attributable to a circumstellar dust disk. Nonetheless, the ground-based optical spectra show a very weak, variable Ca II K absorption line that is phased with the Kepler light curve, being strongest at minimum brightness. We discuss BOKS 53856 and similar objects in the context of a localized enhancement of absorption from metals in dark (possibly magnetic) spots on the white dwarf surface.
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| 68. |
- Hodapp, Klaus W., et al.
(author)
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The New EXor Outburst of ESO-H alpha 99 Observed by Gaia ATLAS and TESS
- 2019
-
In: Astronomical Journal. - : IOP PUBLISHING LTD. - 0004-6256 .- 1538-3881. ; 158:6
-
Journal article (peer-reviewed)abstract
- We report photometry and spectroscopy of the outburst of the young stellar object ESO-H?99. The outburst was first noticed in Gaia alert Gaia18dvc and later by the Asteroid Terrestrial-impact Last Alert System (ATLAS). We have established the outburst light curve with archival ATLAS orange filter photometry, Gaia data, new V-band photometry, and J, H, and K-s photometry from the Infrared Imaging System (IRIS) and the United Kingdom Infrared Telescope (UKIRT). The brightness has fluctuated several times near the light curve maximum. The Transiting Exoplanet Survey Satellite (TESS) satellite observed ESO-H99 with high cadence during one of these minor minima and found brightness fluctuations on timescales of days and hours. Imaging with UKIRT shows the outline of an outflow cavity, and we find one knot of emission, now named MHO 1520, on the symmetry axis of this nebula, indicating recent collimated outflow activity from ESO-H99. Its pre-outburst SED shows a flat far-infrared spectrum, confirming its early evolutionary state and its similarity to other deeply embedded objects in the broader EXor class. The pre-outburst luminosity is 34 L, a much higher luminosity than typical EXors, indicating that ESO-H alpha 99 may be a star of intermediate mass. Infrared and optical spectroscopy show a rich emission-line spectrum, including H i lines, strong red Ca ii emission, as well as infrared CO bandhead emission, all characteristic EXors in the broadest sense. Comparison of the present spectra with an optical spectrum obtained in 1993, presumably in the quiescent state of the object, shows that during the present outburst the continuum component of the spectrum has increased notably more than the emission lines. The H alpha equivalent width during the outburst is down to one-half of its 1993 level, and shock-excited emission lines are much less prominent.
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| 69. |
- Hunter, Deidre A., et al.
(author)
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A Comparison of Young Star Properties with Local Galactic Environment for LEGUS/LITTLE THINGS Dwarf Irregular Galaxies
- 2018
-
In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 156:1
-
Journal article (peer-reviewed)abstract
- We have explored the role environmental factors play in determining characteristics of young stellar objects in nearby dwarf irregular and blue compact dwarf galaxies. Star clusters are characterized by concentrations, masses, and formation rates; OB associations by mass and mass surface density; O stars by their numbers and near-ultraviolet absolute magnitudes; and H II regions by H alpha surface brightnesses. These characteristics are compared to surrounding galactic pressure, stellar mass density, H I surface density, and star formation rate (SFR) surface density. We find no trend of cluster characteristics with environmental properties, implying that larger-scale effects are more important in determining cluster characteristics or that rapid dynamical evolution erases any memory of the initial conditions. On the other hand, the most massive OB associations are found at higher pressure and H I surface density, and there is a trend of higher H II region H alpha surface brightness with higher pressure, suggesting that a higher concentration of massive stars and gas is found preferentially in regions of higher pressure. At low pressures we find massive stars but not bound clusters and OB associations. We do not find evidence for an increase of cluster formation efficiency as a function of SFR density. However, there is an increase in the ratio of the number of clusters to the number of O stars with increasing pressure, perhaps reflecting an increase in clustering properties with SFR.
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| 70. |
- Johnson, Owen A., et al.
(author)
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A Simultaneous Dual-site Technosignature Search Using International LOFAR Stations
- 2023
-
In: Astronomical Journal. - 1538-3881 .- 0004-6256. ; 166:5
-
Journal article (peer-reviewed)abstract
- The Search for Extraterrestrial Intelligence aims to find evidence of technosignatures, which can point toward the possible existence of technologically advanced extraterrestrial life. Radio signals similar to those engineered on Earth may be transmitted by other civilizations, motivating technosignature searches across the entire radio spectrum. In this endeavor, the low-frequency radio band has remained largely unexplored; with prior radio searches primarily above 1 GHz. In this survey at 110-190 MHz, observations of 1,631,198 targets from TESS and Gaia are reported. Observations took place simultaneously with two international stations (noninterferometric) of the Low Frequency Array in Ireland and Sweden. We can reject the presence of any Doppler drifting narrowband transmissions in the barycentric frame of reference, with equivalent isotropic radiated power of 1017 W, for 0.4 million (or 1.3 million) stellar systems at 110 (or 190) MHz. This work demonstrates the effectiveness of using multisite simultaneous observations for rejecting anthropogenic signals in the search for technosignatures.
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