Person:

Goodman, Alyssa

We present two Very Large Array observations of the pre-main-sequence star PV Cephei, taken with a separation of 10.5 years. These data show that the proper motions of this star are (\mu_{\alpha} = +10.9 \pm 3.0 \ mas \ yr^{-1}); (\mu_{\delta} +0.2 \pm 1.8 \ mas \ yr^{-1}), very similar to those – previously known – of HD 200775, the B2Ve star that dominates the illumination of the nearby reflection nebula NGC 7023. This result suggests that PV Cephei is not a rapidly moving run-away star as suggested by previous studies. The large velocity of PV Cephei had been inferred from the systematic eastward displacement of the bisectors of successive pairs of Herbig Haro knots along its flow. These systematic shifts might instead result from an intrinsic dissymmetry in the ejection mechanisms, or from an asymmetric distribution of the circumstellar material.

In this work, we present a detailed study of the rotational properties of magnetized and self-gravitating dense molecular cloud cores formed in a set of two very high resolution three-dimensional molecular cloud simulations with decaying turbulence. The simulations have been performed using the adaptative mesh refinement code RAMSES with an effective resolution of (4096^3) grid cells. One simulation represents a mildly magnetically-supercritical cloud and the other a strongly magnetically-supercritical cloud. We identify dense cores at a number of selected epochs in the simulations at two density thresholds which roughly mimick the excitation densities of the (NH_{3} (J − K)=(1,1)) transition and the (N_{2}H^{+}(1-0)) emission line. A noticeable global difference between the two simulations is the core formation efficiency (CFE) of the high density cores. In the strongly supercritical simulations the CFE is 33 percent per unit free-fall time of the cloud ((t_{ff,cl})), whereas in the mildly supercritical simulations this value goes down to (\sim 6) percent per unit (t_{ff,cl}). A comparison of the intrinsic specific angular momentum ((j_{3D})) distributions of the cores with the specific angular momentum derived using synthetic two-dimensional velocity maps of the cores ((j_{3D})) , shows that the synthetic observations tend to overestimate the true value of the specific angular momentum by a factor of (\sim 8−10). We find that the distribution of the ratio (j_{3D}/j_{2D}) of the cores peaks at around (\sim 0.1). The origin of this discrepancy lies in the fact that contrary to the intrinsic determination of j which sums up the individual gas parcels contributions to the angular momentum, the determination of the specific angular momentum using the standard observational procedure which is based on a measurement on the global velocity gradient under the hypothesis of uniform rotation smoothes out the complex fluctuations present in the three-dimensional velocity field. Our results may well provide a natural explanation for the discrepancy by a factor ∼ 10 observed between the intrinsic three-dimensional distributions of the specific angular momentum and the corresponding distributions derived in real observations. We suggest that previous and future measurements of the specific angular momentum of dense cores which are based on the measurement of the observed global velocity gradients may need to be reduced by a factor of (\sim 10) in order to derive a more accurate estimate of the true specific angular momentum in the cores. We also show that the exponent of the size-specific angular momentum relation are smaller ((\sim 1.4)) in the synthetic observations than their values derived in the three-dimensional space ((\sim 1.8)).

We present a study of dense structures in the L1495 filament in the Taurus Molecular Cloud and examine its star-forming properties. In particular we construct a dust extinction map of the filament using deep near-infrared observations, exposing its small-scale structure in unprecedented detail. The filament shows highly fragmented substructures and a high mass-per-length value of (M_{line} = 17 M \odot \ pc^{-1}), reflecting star-forming potential in all parts of it. However, a part of the filament, namely B211, is remarkably devoid of young stellar objects. We argue that in this region the initial filament collapse and fragmentation is still taking place and star formation is yet to occur. In the star-forming part of the filament, we identify 39 cores with masses from (0.4 to 10 M \odot) and preferred separations in agreement with the local Jeans length. Most of these cores exceed the Bonnor-Ebert critical mass, and are therefore likely to collapse and form stars. The Dense Core Mass Function follows a power law with exponent (\lceil = 1.2 \pm 0.2), a form commonly observed in star-forming regions.

We utilize the extensive datasets available for the Perseus molecular cloud to analyze the relationship between the kinematics of small-scale dense cores and the larger structures in which they are embedded. The kinematic measures presented here can be used in conjunction with those discussed in our previous work as strong observational constraints that numerical simulations (or analytic models) of star formation should match. We find that dense cores have small motions with respect to the (^{13}CO) gas, about one third of the (^{13}CO) velocity dispersion along the same line of sight. Within each extinction region, the core- to-core velocity dispersion is about half of the total ((^{13}CO)) velocity dispersion seen in the region. Large-scale velocity gradients account for roughly half of the total velocity dispersion in each region, similar to what is predicted from large-scale turbulent modes following a power spectrum of (P(k) \alpha \ k^{−4}).

We give a brief overview of some key features of WorldWide Telescope and its Ambassadors Program, and we describe two goals for expanding the program in the coming year: scaling up training efforts; and developing “plug and play” Visualization Lab modules that teach key Earth and Space Science concepts to students while emphasizing important scientific processes and skills. We discuss several different ways that members of the astronomy education and outreach community can incorporate WWT-based materials into their work.

We report preliminary results from an NSF-funded project to build, test, and research the impact of a WorldWide Telescope Visualization Lab (WWT Vizlab), meant to offer learners a deeper physical understanding of the causes of the Moon's phases. The Moon Phases VizLab is designed to promote accurate visualization of the complex, three dimensional Earth-Sun-Moon relationships required to understand the Moon's phases, while also providing opportunities for middle school students to practice critical science skills, like using models, making predictions and observations, and linking them in evidence-based explanations. In the VizLab, students use both computer-based models and lamp + ball physical models. We present findings from the first two phases of the study---one in which we compared learning gains from the WWT VizLab with a traditional two dimensional Moon phases simulator, and another in which we experimented with different ways of blending physical and virtual models in the classroom.

We present Brut, an algorithm to identify bubbles in infrared images of the Galactic midplane. Brut is based on the Random Forest algorithm, and uses bubbles identified by >35,000 citizen scientists from the Milky Way Project to discover the identifying characteristics of bubbles in images from the Spitzer Space Telescope. We demonstrate that Brut's ability to identify bubbles is comparable to expert astronomers. We use Brut to re-assess the bubbles in the Milky Way Project catalog, and find that 10%-30% of the objects in this catalog are non-bubble interlopers. Relative to these interlopers, high-reliability bubbles are more confined to the mid-plane, and display a stronger excess of young stellar objects along and within bubble rims. Furthermore, Brut is able to discover bubbles missed by previous searches—particularly bubbles near bright sources which have low contrast relative to their surroundings. Brut demonstrates the synergies that exist between citizen scientists, professional scientists, and machine learning techniques. In cases where "untrained" citizens can identify patterns that machines cannot detect without training, machine learning algorithms like Brut can use the output of citizen science projects as input training sets, offering tremendous opportunities to speed the pace of scientific discovery. A hybrid model of machine learning combined with crowdsourced training data from citizen scientists can not only classify large quantities of data, but also address the weakness of each approach if deployed alone.

The ADS All-Sky Survey (ADSASS) is an ongoing effort aimed at turning the NASA Astrophysics Data System (ADS), widely known for its unrivaled value as a literature resource for astronomers, into a data resource. The ADS is not a data repository per se, but it implicitly contains valuable holdings of astronomical data, in the form of images, tables and object references contained within articles. The objective of the ADSASS effort is to extract these data and make them discoverable and available through existing data viewers. The resulting ADSASS data layer promises to greatly enhance workflows and enable new research by tying astronomical literature and data assets into one resource.

The WorldWide Telescope computer program, released to researchers and the public as a free resource in 2008 by Microsoft Research, has changed the way the ever-growing Universe of online astronomical data is viewed and understood. The WWT program can be thought of as a scriptable, interactive, richly visual browser of the multi-wavelength Sky as we see it from Earth, and of the Universe as we would travel within it. In its web API format, WWT is being used as a service to display professional research data. In its desktop format, WWT works in concert (thanks to SAMP and other IVOA standards) with more traditional research applications such as ds9, Aladin and TOPCAT. The WWT Ambassadors Program (founded in 2009) recruits and trains astrophysically-literate volunteers (including retirees) who use WWT as a teaching tool in online, classroom, and informal educational settings. Early quantitative studies of WWTA indicate that student experiences with WWT enhance science learning dramatically. Thanks to the wealth of data it can access, and the growing number of services to which it connects, WWT is now a key linking technology in the Seamless Astronomy environment we seek to offer researchers, teachers, and students alike.

Classical T Tauri stars (CTTS) are low-mass pre-main sequence objects surrounded by an accretion disk and still partially embedded in the parent circumstellar cloud. We observed a sample of 20 CTTS covering different ages and evolutionary stages with VLT/X-Shooter. Its wide wavelength coverage allows to simultaneously observe H I lines in the Balmer, Paschen, and Brackett series, which supposedly originate mainly from the accretion funnel. We present the results of our study of reddening in CTTS using ratios of common upper level lines. We determine new extinction values AV for several objects, but cannot find deviations from the standard parametrisation A=AV*lambda^-1.84 (Martin & Whittet 1990) of the reddening at infrared wavelengths.