ORCID Profile
0000-0001-9982-1332
Current Organisation
The University of Texas at Austin
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Publisher: American Astronomical Society
Date: 04-04-2017
Publisher: American Astronomical Society
Date: 11-08-2017
Publisher: American Astronomical Society
Date: 07-12-2017
Publisher: American Astronomical Society
Date: 08-2021
Publisher: American Astronomical Society
Date: 12-2022
Abstract: Young stellar populations provide a record of past star formation, and by establishing their members’ dynamics and ages, it is possible to reconstruct the full history of star formation events. Gaia has greatly expanded the number of accessible stellar populations, with one of the most notable recently discovered associations being Cepheus Far North (CFN), a population containing hundreds of members spanning over 100 pc. With its proximity ( d ≲ 200 pc), apparent substructure, and relatively small population, CFN represents a manageable population to study in depth, with enough evidence of internal complexity to produce a compelling star formation story. Using Gaia astrometry and photometry combined with additional spectroscopic observations, we identify over 500 candidate CFN members spread across seven subgroups. Combining ages from isochrones, asteroseismology, dynamics, and lithium depletion, we produce well-constrained ages for all seven subgroups, revealing a largely continuous 10 Myr star formation history in the association. By tracing back the present-day populations to the time of their formation, we identify two spatially and dynamically distinct nodes in which stars form, one associated with β Cephei, which shows mostly co-spatial formation, and one associated with EE Draconis with a more dispersed star formation history. This detailed view of star formation demonstrates the complexity of the star formation process, even in the smallest of regions.
Publisher: American Astronomical Society
Date: 14-11-2017
Publisher: American Astronomical Society
Date: 15-10-2018
Publisher: American Astronomical Society
Date: 12-06-2019
Publisher: American Astronomical Society
Date: 09-03-2022
Abstract: Mature super-Earths and sub-Neptunes are predicted to be ≃ Jovian radius when younger than 10 Myr. Thus, we expect to find 5–15 R ⊕ planets around young stars even if their older counterparts harbor none. We report the discovery and validation of TOI 1227b, a 0.85 ± 0.05 R J (9.5 R ⊕ ) planet transiting a very-low-mass star (0.170 ± 0.015 M ⊙ ) every 27.4 days. TOI 1227's kinematics and strong lithium absorption confirm that it is a member of a previously discovered subgroup in the Lower Centaurus Crux OB association, which we designate the Musca group. We derive an age of 11 ± 2 Myr for Musca, based on lithium, rotation, and the color–magnitude diagram of Musca members. The TESS data and ground-based follow-up show a deep (2.5%) transit. We use multiwavelength transit observations and radial velocities from the IGRINS spectrograph to validate the signal as planetary in nature, and we obtain an upper limit on the planet mass of ≃0.5 M J . Because such large planets are exceptionally rare around mature low-mass stars, we suggest that TOI 1227b is still contracting and will eventually turn into one of the more common R ⊕ planets.
Publisher: American Astronomical Society
Date: 24-06-2020
Publisher: American Astronomical Society
Date: 10-01-2017
Publisher: American Astronomical Society
Date: 18-08-2016
Publisher: American Astronomical Society
Date: 04-02-2020
Publisher: American Astronomical Society
Date: 11-2021
Abstract: HIP 67522 b is a 17 Myr old, close-in ( P orb = 6.96 days), Jupiter-sized ( R = 10 R ⊕ ) transiting planet orbiting a Sun-like star in the Sco–Cen OB association. We present our measurement of the system’s projected orbital obliquity via two spectroscopic transit observations using the CHIRON spectroscopic facility. We present a global model that accounts for large surface brightness features typical of such young stars during spectroscopic transit observations. With a value of ∣ λ ∣ = 5.8 − 5.7 + 2.8 ° it is unlikely that this well-aligned system is the result of a high-eccentricity-driven migration history. By being the youngest planet with a known obliquity, HIP 67522 b holds a special place in contributing to our understanding of giant planet formation and evolution. Our analysis shows the feasibility of such measurements for young and very active stars.
Publisher: American Astronomical Society
Date: 03-08-2016
Publisher: American Astronomical Society
Date: 03-08-2016
Publisher: American Astronomical Society
Date: 31-03-2020
Publisher: American Astronomical Society
Date: 02-01-2020
Publisher: American Astronomical Society
Date: 25-01-2019
Publisher: American Astronomical Society
Date: 22-06-2020
Publisher: American Astronomical Society
Date: 29-04-2019
Publisher: American Astronomical Society
Date: 29-03-2018
Publisher: American Astronomical Society
Date: 22-01-2019
Publisher: American Astronomical Society
Date: 30-06-2017
Publisher: Zenodo
Date: 2016
DOI: 10.5281/ZENODO.58758
Publisher: American Astronomical Society
Date: 14-01-2021
Publisher: American Astronomical Society
Date: 12-10-2018
Publisher: American Astronomical Society
Date: 16-12-2019
Publisher: American Astronomical Society
Date: 22-06-2017
Publisher: Oxford University Press (OUP)
Date: 04-02-2022
Abstract: Planet formation is often considered in the context of one circumstellar disc around one star. Yet, stellar binary systems are ubiquitous, and thus a substantial fraction of all potential planets must form and evolve in more complex, dynamical environments. We present the results of a 5 yr astrometric monitoring c aign studying 45 binary star systems that host Kepler planet candidates. The planet-forming environments in these systems would have literally been shaped by the binary orbits that persist to the present day. Crucially, the mutual inclinations of star–planet orbits can only be addressed by a statistical s le. We describe in detail our s le selection and Keck/NIRC2 laser guide star adaptive optics observations collected from 2012 to 2017. We measure orbital arcs, with a typical accuracy of ∼0.1 mas yr−1, that test whether the binary orbits tend to be aligned with the edge-on transiting planet orbits. We rule out randomly distributed binary orbits at 4.7σ, and we show that low mutual inclinations are required to explain the observed orbital arcs. If the stellar orbits have a field binary-like eccentricity distribution, then the best match to our observed orbital arcs is a distribution of mutual inclinations ranging from 0° to 30°. We discuss the implications of such widespread planet–binary alignment in the theoretical context of planet formation and circumstellar disc evolution.
Publisher: American Astronomical Society
Date: 06-07-2018
Publisher: American Astronomical Society
Date: 09-03-2021
Abstract: The detection and characterization of young planetary systems offer a direct path to study the processes that shape planet evolution. We report on the discovery of a sub-Neptune-sized planet orbiting the young star HD 110082 (TOI-1098). Transit events we initially detected during TESS Cycle 1 are validated with time-series photometry from Spitzer. High-contrast imaging and high-resolution, optical spectra are also obtained to characterize the stellar host and confirm the planetary nature of the transits. The host star is a late-F dwarf ( M ⋆ = 1.2 M ⊙ ) with a low-mass, M dwarf binary companion ( M ⋆ = 0.26 M ⊙ ) separated by nearly one arcminute (∼6200 au). Based on its rapid rotation and Lithium absorption, HD 110082 is young, but is not a member of any known group of young stars (despite proximity to the Octans association). To measure the age of the system, we search for coeval, phase-space neighbors and compile a s le of candidate siblings to compare with the empirical sequences of young clusters and to apply quantitative age-dating techniques. In doing so, we find that HD 110082 resides in a new young stellar association we designate MELANGE-1, with an age of Myr. Jointly modeling the TESS and Spitzer light curves, we measure a planetary orbital period of 10.1827 days and radius of R p = 3.2 ± 0.1 R ⊕ . HD 110082 b’s radius falls in the largest 12% of field-age systems with similar host-star mass and orbital period. This finding supports previous studies indicating that young planets have larger radii than their field-age counterparts.
Publisher: American Astronomical Society
Date: 29-08-2023
Abstract: Young stellar populations provide a powerful record that traces millions of years of star formation history in the solar neighborhood. Using a revised form of the SPYGLASS young star identification methodology, we produce an expanded census of nearby young stars (age 50 Myr). We then use the HDBSCAN clustering algorithm to produce a new SPYGLASS Catalog of Young Associations, which reveals 116 young associations within 1 kpc. More than 25% of these groups are largely new discoveries, as 20 are substantively different from any previous definition, and 10 have no equivalent in the literature. The new associations reveal a yet undiscovered demographic of small associations with little connection to larger structures. Some of the groups we identify are especially unique for their high transverse velocities, which can differ from the solar velocity by 30–50 km s −1 , and for their positions, which can reach up to 300 pc above the galactic plane. These features may suggest a unique origin, matching existing evidence of infalling gas parcels interacting with the disk interstellar medium. Our clustering also suggests links between often-separated populations, hinting to direct structural connections between Orion Complex and Perseus OB2, and between the subregions of Vela. The ∼30 Myr old Cepheus-Hercules association is another emerging large-scale structure, with a size and population comparable to Sco-Cen. Cep-Her and other similarly aged structures are also found clustered along extended structures perpendicular to known spiral arm structure, suggesting that arm-aligned star formation patterns have only recently become dominant in the solar neighborhood.
Publisher: American Astronomical Society
Date: 19-09-2019
Abstract: Planets occur most frequently around cool dwarfs, but only a handful of specific ex les are known to orbit the latest-type M stars. Using TESS photometry, we report the discovery of two planets transiting the low-mass star called LP 791-18 (identified by TESS as TOI 736). This star has spectral type M6V, effective temperature 2960 K, and radius 0.17 R ⊙ , making it the third-coolest star known to host planets. The two planets straddle the radius gap seen for smaller exoplanets they include a 1.1 R ⊕ planet on a 0.95 day orbit and a 2.3 R ⊕ planet on a 5 day orbit. Because the host star is small the decrease in light during these planets’ transits is fairly large (0.4% and 1.7%). This has allowed us to detect both planets’ transits from ground-based photometry, refining their radii and orbital ephemerides. In the future, radial velocity observations and transmission spectroscopy can both probe these planets’ bulk interior and atmospheric compositions, and additional photometric monitoring would be sensitive to even smaller transiting planets.
Publisher: American Astronomical Society
Date: 28-09-2017
Publisher: American Astronomical Society
Date: 24-09-2020
Publisher: American Astronomical Society
Date: 18-08-2021
Publisher: American Astronomical Society
Date: 12-2022
Abstract: The study of young associations is essential for building a complete record of local star formation processes. The Fornax–Horologium association (FH), including the χ 1 Fornacis cluster, represents one of the nearest young stellar populations to the Sun. This association has recently been linked to the Tuc-Hor, Carina, and Columba associations, building an extensive “Austral Complex” almost entirely within 150 pc. Using Gaia astrometry and photometry in addition to new spectroscopic observations, we perform the deepest survey of FH to date, identifying over 300 candidate members, nearly doubling the known population. By combining this s le with literature surveys of the other constituent populations, we produce a contiguous stellar population covering the entire Austral Complex, allowing the definitions of subpopulations to be reassessed along with connections to external populations. This analysis recovers new definitions for FH, Tuc-Hor, Columba, and Carina, while also revealing a connection between the Austral complex and the Sco-Cen-affiliated Platais 8 cluster. This suggests that the Austral complex may be just a small component of a much larger and more erse star formation event. Computing ages and tracing stellar populations back to formation reveals two distinct nodes of cospatial and continuous formation in the Austral Complex, one containing Tuc-Hor, and the other containing FH, Carina, and Columba. This mirrors recent work showing similar structure elsewhere, suggesting that these nodes, which only emerge through the use of traceback, may represent the clearest discrete unit of local star formation, and a key building block needed to reconstruct larger star-forming events.
Publisher: American Astronomical Society
Date: 23-07-2019
No related grants have been discovered for Aaron Rizzuto.