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  1. Free, publicly-accessible full text available January 31, 2025
  2. Abstract

    Molecular emission is used to investigate both the physical and chemical properties of protoplanetary disks. Therefore, to derive disk properties accurately, we need a thorough understanding of the behavior of the molecular probes upon which we rely. Here we investigate how the molecular line emission of N2H+, HCO+, HCN, and C18O compare to other measured quantities in a set of 20 protoplanetary disks. Overall, we find positive correlations between multiple line fluxes and the disk dust mass and radius. We also generally find strong positive correlations between the line fluxes of different molecular species. However, some disks do show noticeable differences in the relative fluxes of N2H+, HCO+, HCN, and C18O. These differences occur even within a single star-forming region. This results in a potentially large range of different disk masses and chemical compositions for systems of similar age and birth environment. While we make preliminary comparisons of molecular fluxes across different star-forming regions, more complete and uniform samples are needed in the future to search for trends with birth environment or age.

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  3. Recent research conducted in southern Sonora, Mexico provides an opportunity to revisit debates about interaction between Mesoamerica and the North American Southwest (NAS). In the borderland between these traditions, communities show few signs of cultural amalgamation, instead exhibiting either an avoidance of overt identity markers or an emphasis on more local connections. This pattern contrasts with most discussions of Mesoamerican influence on the NAS that focus on regionally atypical centers of foreign goods consumption or evidence of foreign religious traditions in distant localities. By recentering on local contexts where cultural amalgamation is expected but minimal, we raise important questions about why more distant groups found Mesoamerican societies to be worthy of emulation. The results suggest researchers should devote equal attention to cases in which distinct identities are erased or suppressed as they do to cases in which social boundaries are maintained or created anew. 
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    Free, publicly-accessible full text available September 25, 2024
  4. The Huatabampo tradition was first defined by Gordon Ekholm, in 1938, and refers to those sites in the coastal plain in northern Sinaloa and southern Sonora lacking architecture but containing well-manufactured plain ceramics with complex shapes. Recent investigations in the region are helping to refine the chronology, geographical extension, cultural attributes, and ethnicity. With 20 radiocarbon dates, we can place this tradition as spanning from 200 BC to AD 1450. The maximum geographical extension ranges from the Middle Rio Yaqui in the north to the Rio San Lorenzo in Sinaloa. The associated sites of this complex are represented by dispersed houses, indicative of ranchería-type settlements, funerary mounds, shell middens, and petroglyph sites. At about AD 1150, Aztatlán pottery and other commodities from southern Sinaloa were incorporated mostly as mortuary offerings. We also provide evidence that the Huatabampo archaeological tradition is a local culture representing the occupation of the Cahitan-speaking groups, Yoremem/Mayos and Yoemem/Yaquis, of the coastal plain. 
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    Free, publicly-accessible full text available July 11, 2024
  5. This article revises the spatial and temporal boundaries of the Casas Grandes tradition associated with northwest Chihuahua, Mexico, based on new data collected in neighboring northeastern Sonora. The Casas Grandes tradition attained its greatest extent during the Medio period (AD 1200–1450/1500) followed by a dramatic demographic and political collapse. Hunter-gatherer groups subsequently occupied most of northwest Chihuahua. Data from the Fronteras Valley, Sonora, presents an alternative scenario, with a clear pattern of cultural continuity from the eleventh century to the colonial period in which sedentary farmers occupied the same landscapes and occasionally the same villages. These observations contribute to our understanding of the spread and subsequent demise of the Casas Grandes tradition in hinterland regions. For the Fronteras Valley, we infer that immigrant groups originally introduced Casas Grandes traditions and that uneven participation in a suite of shared religious beliefs and practices was common to all the hinterlands.

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    Free, publicly-accessible full text available June 1, 2024
  6. Abstract We present Atacama Large Millimeter/submillimeter Array observations of the ∼10,000 au environment surrounding 21 protostars in the Orion A molecular cloud tracing outflows. Our sample is composed of Class 0 to flat-spectrum protostars, spanning the full ∼1 Myr lifetime. We derive the angular distribution of outflow momentum and energy profiles and obtain the first two-dimensional instantaneous mass, momentum, and energy ejection rate maps using our new approach: the pixel flux-tracing technique. Our results indicate that by the end of the protostellar phase, outflows will remove ∼2–4 M ⊙ from the surrounding ∼1 M ⊙ low-mass core. These high values indicate that outflows remove a significant amount of gas from their parent cores and continuous core accretion from larger scales is needed to replenish core material for star formation. This poses serious challenges to the concept of cores as well-defined mass reservoirs , and hence to the simplified core-to-star conversion prescriptions. Furthermore, we show that cavity opening angles, and momentum and energy distributions all increase with protostar evolutionary stage. This is clear evidence that even garden-variety protostellar outflows: (a) effectively inject energy and momentum into their environments on 10,000 au scales, and (b) significantly disrupt their natal cores, ejecting a large fraction of the mass that would have otherwise fed the nascent star. Our results support the conclusion that protostellar outflows have a direct impact on how stars get their mass, and that the natal sites of individual low-mass star formation are far more dynamic than commonly accepted theoretical paradigms. 
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  7. Abstract

    Gas mass is a fundamental quantity of protoplanetary disks that directly relates to their ability to form planets. Because we are unable to observe the bulk H2content of disks directly, we rely on indirect tracers to provide quantitative mass estimates. Current estimates for the gas masses of the observed disk population in the Lupus star-forming region are based on measurements of isotopologues of CO. However, without additional constraints, the degeneracy between H2mass and the elemental composition of the gas leads to large uncertainties in such estimates. Here, we explore the gas compositions of seven disks from the Lupus sample representing a range of CO-to-dust ratios. With Band 6 and 7 ALMA observations, we measure line emission for HCO+, HCN, and N2H+. We find a tentative correlation among the line fluxes for these three molecular species across the sample, but no correlation with13CO or submillimeter continuum fluxes. For the three disks where N2H+is detected, we find that a combination of high disk gas masses and subinterstellar C/H and O/H are needed to reproduce the observed values. We find increases of ∼10–100× previous mass estimates are required to match the observed line fluxes. This work highlights how multimolecular studies are essential for constraining the physical and chemical properties of the gas in populations of protoplanetary disks, and that CO isotopologues alone are not sufficient for determining the mass of many observed disks.

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  8. null (Ed.)