Browsing by Author "Reiter, Megan"
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Item A probable Keplerian disk feeding an optically revealed massive young star(Springer Nature, 2024) McLeod, Anna F.; Klaassen, Pamela D.; Reiter, Megan; Henshaw, Jonathan; Kuiper, Rolf; Ginsburg, AdamThe canonical picture of star formation involves disk-mediated accretion, with Keplerian accretion disks and associated bipolar jets primarily observed in nearby, low-mass young stellar objects (YSOs). Recently, rotating gaseous structures and Keplerian disks have been detected around several massive (M > 8 M⊙) YSOs (MYSOs)1–4, including several disk-jet systems5–7. All the known MYSO systems are in the Milky Way, and all are embedded in their natal material. Here we report the detection of a rotating gaseous structure around an extragalactic MYSO in the Large Magellanic Cloud. The gas motion indicates that there is a radial flow of material falling from larger scales onto a central disk-like structure. The latter exhibits signs of Keplerian rotation, so that there is a rotating toroid feeding an accretion disk and thus the growth of the central star. The system is in almost all aspects comparable to Milky Way high-mass YSOs accreting gas from a Keplerian disk. The key difference between this source and its Galactic counterparts is that it is optically revealed rather than being deeply embedded in its natal material as is expected of such a massive young star. We suggest that this is the consequence of the star having formed in a low-metallicity and low-dust content environment. Thus, these results provide important constraints for models of the formation and evolution of massive stars and their circumstellar disks.Item Demographics of the M-star Multiple Population in the Orion Nebula Cluster(IOP Publishing, 2022) Furio, Matthew De; Liu, Christopher; Meyer, Michael R.; Reiter, Megan; Kraus, Adam; Dupuy, Trent; Monnier, JohnWe present updated results constraining multiplicity demographics for the stellar population of the Orion Nebula Cluster (ONC, a high-mass, high-density star-forming region), across primary masses 0.08–0.7 M ⊙. Our study utilizes archival Hubble Space Telescope data obtained with the Advanced Camera for Surveys using multiple filters (GO-10246). Previous multiplicity surveys in low-mass, low-density associations like Taurus identify an excess of companions to low-mass stars roughly twice that of the Galactic field and find the mass ratio distribution consistent with the field. Previously, we found the companion frequency to low-mass stars in the ONC is consistent with the Galactic field over mass ratios = 0.6–1.0 and projected separations = 30–160 au, without placing constraints on the mass ratio distribution. In this study, we investigate the companion population of the ONC with a double point-spread function (PSF) fitting algorithm sensitive to separations larger than 10 au (0.″025) using empirical PSF models. We identified 44 companions (14 new), and with a Bayesian analysis we estimate the companion frequency to low-mass stars in the ONC = 0.13 and the index of the power-law fit to the mass ratio distribution = 2.08 over all mass ratios and projected separations of 10–200 au. We find the companion frequency in the ONC is consistent with the Galactic field population, likely from states of high transient stellar density, and a probability of 0.002 that it is consistent with that of Taurus. We also find the ONC mass ratio distribution is consistent with the field and Taurus, potentially indicative of its primordial nature, a direct outcome of the star formation process.Item Dynamics of young stellar clusters as planet-forming environments(Springer Nature, 2022) Reiter, Megan; Parker, Richard J.Most stars and thus most planetary systems do not form in isolation. The larger star-forming environment affects protoplanetary disks in multiple ways: Gravitational interactions with other stars truncate disks and alter the architectures of exoplanet systems; external irradiation from nearby high-mass stars truncates disks and shortens their lifetimes; and the remaining gas and dust in the environment affect dynamical evolution (if removed by feedback processes) and provide some shielding for disks from external irradiation. The dynamical evolution of the region regulates when and how long various feedback mechanisms impact protoplanetary disks. Density is a key parameter that regulates the intensity and duration of UV irradiation and the frequency of dynamical encounters. The evolution of larger star-forming complexes may also play an important role by mixing populations. Observations suggest that clusters are not a single-age population but multiple populations with small age differences, which may be key to resolving several timescale issues (i.e., proplyd lifetimes, enrichment). In this review, we consider stellar clusters as the ecosystems in which most stars and therefore most planets form. We review recent observational and theoretical results and highlight upcoming contributions from facilities expected to begin observations in the next 5 years. Looking further ahead, we argue that the next frontier is large-scale surveys of low-mass stars in more distant high-mass star-forming regions. The future of ecosystem studies is bright as faint low-mass stars in more distant high-mass star-forming regions will be routinely observable in the era of extremely large telescopes.Item Fast-rotating Blue Straggler Stars in the Globular Cluster NGC 3201*(IOP Publishing Ltd, 2023) Billi, Alex; Ferraro, Francesco R.; Mucciarelli, Alessio; Lanzoni, Barbara; Cadelano, Mario; Monaco, Lorenzo; Mateo, Mario; Bailey, John I.; Reiter, Megan; Olszewski, Edward W.We used high-resolution spectra acquired with the Magellan Telescope to measure radial and rotational velocities of approximately 200 stars in the Galactic globular cluster NGC 3201. The surveyed sample includes blue straggler stars (BSSs) and reference stars in different evolutionary stages (main-sequence turnoff, subgiant, red giant, and asymptotic giant branches). The average radial velocity value (〈V r 〉 = 494.5 ± 0.5 km s−1) confirms a large systemic velocity for this cluster and was used to distinguish 33 residual field interlopers. The final sample of member stars has 67 BSSs and 114 reference stars. Similarly to what is found in other clusters, the totality of the reference stars has negligible rotation (< 20 km s−1), while the BSS rotational velocity distribution shows a long tail extending up to ∼200 km s−1, with 19 BSSs (out of 67) spinning faster than 40 km s−1. This sets the percentage of fast-rotating BSSs to ∼28%. Such a percentage is roughly comparable to that measured in other loose systems (ω Centauri, M4, and M55) and significantly larger than that measured in high-density clusters (as 47 Tucanae, NGC 6397, NGC 6752, and M30). This evidence supports a scenario where recent BSS formation (mainly from the evolution of binary systems) is occurring in low-density environments. We also find that the BSS rotational velocity tends to decrease for decreasing luminosity and surface temperature, similarly to what is observed in main-sequence stars. Hence, further investigations are needed to understand the impact of BSS internal structure on the observed rotational velocities.Item INSTILL: Instructor Network to Support Teaching Innovation and eLevate Learning, 2023-2024(Rice University, 2024) Beason-Abmayr, Beth; Bennaji, Charla; Emami, Maryam; Ferguson, Todd; Gallant, Denva; Houlik-Ritchey, Emily; Powers, Scott; Reiter, Megan; Takayama, Hiromi; Center for Teaching ExcellenceItem The population of young low-mass stars in Trumpler 14(edp Sciences, 2024) Itrich, Dominika; Testi, Leonardo; Beccari, Giacomo; Manara, Carlo F.; Reiter, Megan; Preibisch, Thomas; McLeod, Anna F.; Rosotti, Giovanni; Klessen, Ralf; Molinari, Sergio; Hennebelle, PatrickMassive star-forming regions are thought to be the most common birth environments in the Galaxy and the only birth places of very massive stars. Their presence in the stellar cluster alters the conditions within the cluster, impacting at the same time the evolution of other cluster members. In principle, copious amounts of ultraviolet radiation produced by massive stars can remove material from outer parts of the protoplanetary discs around low- and intermediate-mass stars in the process of external photoevaporation, effectively reducing the planet formation capabilities of those discs. Here, we present deep VLT/MUSE observations of low-mass stars in Trumpler 14, one of the most massive, young, and compact clusters in the Carina Nebula Complex. We provide spectral and stellar properties of 717 sources and based on the distribution of stellar ages, derive the cluster age of ∼1 Myr. The majority of the stars in our sample have masses ≤1 M⊙, which makes our spectroscopic catalogue the deepest to date in term of mass and proves that detailed investigations of low-mass stars are possible in the massive but distant regions. Spectroscopic studies of low-mass members of the whole Carina Nebula Complex are missing. Our work marks an important step forward towards filling this gap and sets the stage for follow-up investigations of accretion properties in Trumpler 14.Item The VLT MUSE NFM view of outflows and externally photoevaporating discs near the orion bar★(Oxford University Press, 2023) Haworth, Thomas J; Reiter, Megan; O’Dell, C Robert; Zeidler, Peter; Berne, Olivier; Manara, Carlo F; Ballabio, Giulia; Kim, Jinyoung S; Bally, John; Goicoechea, Javier R; Aru, Mari-Liis; Gupta, Aashish; Miotello, AnnaWe present Very Large Telescope/Multi-Unit Spectroscopic Explorer Narrow Field Mode observations of a pair of disc-bearing young stellar objects towards the Orion Bar: 203–504 and 203–506. Both of these discs are subject to external photoevaporation, where winds are launched from their outer regions due to environmental irradiation. Intriguingly, despite having projected separation from one another of only 1.65 arcsec(660 au at 400 pc), 203–504 has a classic teardrop shaped ‘proplyd’ morphology pointing towards θ2 Ori A (indicating irradiation by the EUV of that star, rather than $\rm \theta ^1$ Ori C) but 203–506 has no ionization front, indicating it is not irradiated by stellar EUV at all. However, 203–506 does show [C i] 8727 Å and [O i] 6300 Å in emission, indicating irradiation by stellar FUV. This explicitly demonstrates the importance of FUV irradiation in driving mass loss from discs. We conclude that shielding of 203–506 from EUV is most likely due to its position on the observers side of an ionized layer lying in the foreground of the Huygens Region. We demonstrate that the outflow HH 519, previously thought to be emanating from 203–504 is actually an irradiated cloud edge and identify a new compact outflow from that object approximately along our line of sight with a velocity ∼130 km s−1.Item Why Are (Almost) All the Protostellar Outflows Aligned in Serpens Main?(IOP Publishing, 2024) Green, Joel D.; Pontoppidan, Klaus M.; Reiter, Megan; Watson, Dan M.; Shenoy, Sachindev S.; Manoj, P.; Narang, MayankWe present deep 1.4–4.8 μm JWST-NIRCam imaging of the Serpens Main star-forming region and identify 20 candidate protostellar outflows, most with bipolar structure and identified driving sources. The outflow position angles (PAs) are strongly correlated, and they are aligned within ±24° of the major axis of the Serpens filament. These orientations are further aligned with the angular momentum vectors of the two disk shadows in this region. We estimate that the probability of this number of young stars being coaligned if sampled from a uniform PA distribution is 10−4. This in turn suggests that the aligned protostars, which seem to be at similar evolutionary stages based on their outflow dynamics, formed at similar times with a similar spin inherited from a local cloud filament. Further, there is tentative evidence for a systematic change in average PA between the northwestern and southeastern cluster, as well as increased scatter in the PAs of the southeastern protostars. SOFIA-HAWC+ archival dust polarization observations of Serpens Main at 154 and 214 μm are perpendicular to the dominant jet orientation in the northwestern region in particular. We measure and locate shock knots and edges for all of the outflows and provide an identifying catalog. We suggest that Serpens main is a cluster that formed from an isolated filament and due to its youth retains its primordial outflow alignment.