The Arecibo Galaxy Environment Survey VIII : Discovery of an Isolated Dwarf Galaxy in the Local Volume

The Arecibo Galaxy Environment Survey (AGES) has detected a nearby HI source at a heliocentric velocity of +363 km/s . The object was detected through its neutral hydrogen emission and has an obvious possible optical counterpart in Sloan Digital Sky Survey (SDSS) data (though it does not have an optical redshift measurement). We discuss three possible scenarios for the object : 1) It is within the Local Group, in which case its HI properties are comparable with recently discovered ultra-compact high velocity clouds; 2) It is just behind the Local Group, in which case its optical characteristics are similar to the newly discovered Leo P galaxy; 3) It is a blue compact dwarf galaxy within the local volume but not associated with the Local Group. We find the third possibility to be the most likely, based on distance estimates from the Tully-Fisher relation and its velocity relative to the Local Group.Comment: 5 pages, 6 figures, accepted for publication in MNRAS. Minor correction to institution and addres

The Rotation of Young Low-Mass Stars and Brown Dwarfs

We review the current state of our knowledge concerning the rotation and angular momentum evolution of young stellar objects and brown dwarfs from a primarily observational view point. Periods are typically accurate to 1% and available for about 1700 stars and 30 brown dwarfs in young clusters. Discussion of angular momentum evolution also requires knowledge of stellar radii, which are poorly known for pre-main sequence stars. It is clear that rotation rates at a given age depend strongly on mass; higher mass stars (0.4-1.2 M$_\odot$) have longer periods than lower mass stars and brown dwarfs. On the other hand, specific angular momentum is approximately independent of mass for low mass pre-main sequence stars and young brown dwarfs. A spread of about a factor of 30 is seen at any given mass and age. The evolution of rotation of solar-like stars during the first 100 Myr is discussed. A broad, bimodal distribution exists at the earliest observable phases ($\sim$1 Myr) for stars more massive than 0.4 M$_\odot$. The rapid rotators (50-60% of the sample) evolve to the ZAMS with little or no angular momentum loss. The slow rotators continue to lose substantial amounts of angular momentum for up to 5 Myr, creating the even broader bimodal distribution characteristic of 30-120 Myr old clusters. Accretion disk signatures are more prevalent among slowly rotating PMS stars, indicating a connection between accretion and rotation. Disks appear to influence rotation for, at most, $\sim$5 Myr, and considerably less than that for the majority of stars. If the dense clusters studied so far are an accurate guide, then the typical solar-like star may have only $\sim$1 Myr for this task. It appears that both disk interactions and stellar winds are less efficient at braking these objects.Comment: Review chapter for Protostars and Planets V. 15 page and 8 figure

Age spreads in star forming regions?

Rotation periods and projected equatorial velocities of pre-main-sequence (PMS) stars in star forming regions can be combined to give projected stellar radii. Assuming random axial orientation, a Monte-Carlo model is used to illustrate that distributions of projected stellar radii are very sensitive to ages and age dispersions between 1 and 10 Myr which, unlike age estimates from conventional Hertzsprung-Russell diagrams, are relatively immune to uncertainties due to extinction, variability, distance etc. Application of the technique to the Orion Nebula cluster reveals radius spreads of a factor of 2--3 (FWHM) at a given effective temperature. Modelling this dispersion as an age spread suggests that PMS stars in the ONC have an age range larger than the mean cluster age, that could be reasonably described by the age distribution deduced from the Hertzsprung-Russell diagram. These radius/age spreads are certainly large enough to invalidate the assumption of coevality when considering the evolution of PMS properties (rotation, disks etc.) from one young cluster to another.Comment: To appear in "The Ages of Stars", E.E. Mamajek, D.R. Soderblom, R.F.G. Wyse (eds.), IAU Symposium 258, CU

The Arecibo Galaxy Environment Survey VII : A Dense Filament With Extremely Long HI Streams

We present completed observations of the NGC 7448 galaxy group and background volume as part of the blind neutral hydrogen Arecibo Galaxy Environment Survey (AGES). Our observations cover a region spanning 5x4 degrees, over a redshift range of approximately -2,000 < cz < 20,000 km/s. A total of 334 objects are detected, mostly in three overdensities at cz $\sim$7,500, cz $\sim$9,600 and cz $\sim$ 11,400 km/s. The galaxy density is extremely high (15 per square degree) and many ($\sim$24%) show signs of extended HI emission, including some features as much as 800 kpc in projected length. We describe the overall characteristics of this environment : kinematics, typical galaxy colours and mass to light ratios, and substructure. To aid in the cataloguing of this data set, we present a new FITS viewer (FRELLED : Fits Realtime Explorer of Low Latency in Every Dimension). This incorporates interactive source cataloguing tools which increase our source extraction speed by approximately a factor of 50.Comment: 15 pages, 13 figures, accepted for publication in MNRA

Testing the Disk-Locking Paradigm: An Association Between U-V Excess and Rotation in NGC 2264

We present some results from a UVI photometric study of a field in the young open cluster NGC 2264 aimed, in part, at testing whether accretion in pre-main sequence stars is linked to rotation. We confirm that U-V excess is well correlated with H-alpha equivalent width for the stars in our sample. We show that for the more massive stars in the cluster sample (roughly 0.4-1.2 M_sun) there is also a significant association between U-V excess and rotation, in the sense that slow rotators are more likely to show excess U-band emission and variability. This constitutes significant new evidence in support of the disk-locking paradigm.Comment: Accepted by ApJ Letter

Program evaluation of a community-based model for driver off-road assessment in post-acute ABI

Background: Social conditions from the pandemic forced changes to outpatient rehabilitation programs, necessitating pre-driving assessment be administered via telehealth, an alternative model of OT service-delivery. As a result, Shepherd Pathways adapted the clinical pre-driving program for telehealth service delivery. Program outcomes had not been formally assessed. Purpose: The purpose of this Capstone project was to conduct a formal program evaluation to collect, analyze, and use data to evaluate effectiveness and efficiency of a clinical return to drive program delivered via telehealth (CDC, n.d.; The university of Kansas toolbox, n.d.). The program evaluation examined the OT process and scope of services for driver off-road assessment at Shepherd Pathways, in Atlanta, Georgia, and addressed the following objectives. Does Shepherd Pathways clinical pre-driving program meet the needs of acquired brain injury (ABI) clients in a traditional, hybrid, or telehealth model? What are the current practices (assessments and interventions) used within an OT led clinical pre-driving program delivered via telehealth? Does an OT clinical pre-driving program delivered via telehealth result in an on-road driving evaluation (ORDE) outcome of unrestricted driving for ABI clients? Theoretical Framework. A pragmatic research approach (Creswell & Creswell, 2018) and Canadian model of occupational performance-engagement (CMOP-E) and the Ecology of Human Performance (EHP) (Dunn, 1984) influenced the approach. Methods. Program evaluation identified outcomes of a telehealth approach for return to driving. A logic model was used to identify main components of the program and showed relationships among the telehealth pre-driving program goals, objectives, activities, and outcome measurements (Adu, 2017). Results. Research questions were answered-the needs of individuals with ABI were met in the program. OT telehealth clinical standards of practice for the pre-driving program were identified and successful ORDE outcomes indicated a positive relationship between use of telehealth and return to drive after ABI. Conclusions: A logic model illustrated the processes developed for OT driver-off road assessment during the COVID-19 pandemic from March 2020 - December 2020 at Shepherd Pathways. Results indicated a high percentage of program effectiveness, ORDE referrals, and ORDE passing rates for participants with ABI

The Mass Dependence of Stellar Rotation in the Orion Nebula Cluster

We have determined new rotation periods for 404 stars in the Orion Nebula Cluster using the Wide Field Imager attached to the MPG/ESO 2.2 m telescope on La Silla, Chile. Mass estimates are available for 335 of these and most have M < 0.3 M_sun. We confirm the existence of a bimodal period distribution for the higher mass stars in our sample and show that the median rotation rate decreases with increasing mass for stars in the range 0.1 < M <0.4 M_sun. While the spread in angular momentum (J) at any given mass is more than a factor of 10, the majority of lower mass stars in the ONC rotate at rates approaching 30% of their critical break-up velocity, as opposed to 5-10% for solar-like stars. This is a consequence of both a small increase in observed specific angular momentum (j=J/M) and a larger decrease in the critical value of j with decreasing mass. Perhaps the most striking fact, however, is that j varies by so little - less than a factor of two - over the interval 0.1-1.0 M_sun. The distribution of rotation rates with mass in the ONC (age ~ 1 My) is similar in nature to what is found in the Pleiades (age ~ 100 My). These observations provide a significant new guide and test for models of stellar angular momentum evolution during the proto-stellar and pre-main sequence phases.Comment: 11 pages, 3 figure

The Sensitivity of Gas-Phase Chemical Models of Interstellar Clouds to C and O Elemental Abundances and to a New Formation Mechanism for Ammonia

The effects of variations in the gas-phase carbon-to-oxygen elemental abundance ratio (0.42 ≤ C/O ≤ 1.2) and the absolute gas-phase carbon and oxygen elemental abundances on calculated molecular concentrations have been studied for three gas-phase chemical models of dense interstellar clouds. Both the C and O elemental abundances were varied from their "low metal" values, in which C/O = 0.42. The results were compared with observations of the dark interstellar clouds TMC-1 and L134N, the latter being chosen because TMC-1, with its singularly rich component of large hydrocarbons and cyanopolyynes, may not represent dense cores universally. In general, variations in the gas-phase C and O elemental abundances have a large and time-dependent effect on calculated molecular concentrations for all three models. For the "new standard" model, which does not contain many rapid neutral-neutral reactions, excellent "early-time" agreement with TMC-1 occurs for a variety of C/O ratios obtained by depleting the low metal O abundance, but the time of best agreement tends to increase with increasing C/O ratio. At these early times, approx 80% of the calculated abundances are within an order of magnitude of the observed values. Agreement at this level also occurs at steady state if the C and O abundances are first depleted by a factor of 5 and then O is additionally depleted so that C/O ≥ 0.80. In general, a factor of 5 depletion of both C and O increases the production efficiency of large molecules. When the new standard model is applied to L134N, the early-time agreement is not as good as for TMC-1 unless both C and O are first depleted by factors of 5 from their low metal values and the C/O ratio is then maintained at a value less than 0.80. Under these conditions, the steady state results are only slightly worse. The other two models, containing fast neutral-neutral reactions, have their best agreement with TMC-1 when C/O ≥ 1, although the level of agreement is typically worse than with the new standard model, and factor of 5 depletions have little effect. For L134N, on the other hand, the early-time agreement with these latter two models for a wide range of C/O values is almost as good as with the new standard model if factor of 5 depletions in C and O are utilized and is actually superior for most cases when C/O ≥ 1. In general, the negative conclusions concerning models with rapid neutral-neutral reactions may therefore be overly harsh. When the newly studied rapid reaction H+_3+N→NH+_2 + H is included in our model calculations, the abundances of some N-containing species are in better agreement with observed values, but this effect decreases as C/O is increased