2020

Catherine Zucker, Joshua S. Speagle, Edward F. Schlafly, Gregory M. Green, Douglas P. Finkbeiner, Alyssa Goodman, and João Alves. 1/2020. “A Compendium of Distances to Molecular Clouds in the Star Formation Handbook.” Astronomy and Astrophysics, 633, Pp. A51.Abstract
Accurate distances to local molecular clouds are critical for understanding the star and planet formation process, yet distance measurements are often obtained inhomogeneously on a cloud-by-cloud basis. We have recently developed a method that combines stellar photometric data with Gaia DR2 parallax measurements in a Bayesian framework to infer the distances of nearby dust clouds to a typical accuracy of ∼5%. After refining the technique to target lower latitudes and incorporating deep optical data from DECam in the southern Galactic plane, we have derived a catalog of distances to molecular clouds in Reipurth (2008, Star Formation Handbook, Vols. I and II) which contains a large fraction of the molecular material in the solar neighborhood. Comparison with distances derived from maser parallax measurements towards the same clouds shows our method produces consistent distances with ≲10% scatter for clouds across our entire distance spectrum (150 pc-2.5 kpc). We hope this catalog of homogeneous distances will serve as a baseline for future work. Table A.1 is also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/633/A51. It is also available on the Harvard Dataverse at http://https://doi.org/1 0.7910/DVN/07L7YZ An interactive 3D version of Fig. 2 is available at http://https://www.aanda.org
Che-Yu Chen, Erica A. Behrens, Jasmin E. Washington, Laura M. Fissel, Rachel K. Friesen, Zhi-Yun Li, Jaime E. Pineda, and alia. 2020. “Relative Alignment between Dense Molecular Cores and Ambient Magnetic Field: The Synergy of Numerical Models and Observations.” arXiv E-Prints.Abstract

The role played by magnetic field during star formation is an important topic in astrophysics. We investigate the correlation between the orientation of star-forming cores (as defined by the core major axes) and ambient magnetic field directions in 1) a 3D MHD simulation, 2) synthetic observations generated from the simulation at different viewing angles, and 3) observations of nearby molecular clouds. We find that the results on relative alignment between cores and background magnetic field in synthetic observations slightly disagree with those measured in fully 3D simulation data, which is partly because cores identified in projected 2D maps tend to coexist within filamentary structures, while 3D cores are generally more rounded. In addition, we examine the progression of magnetic field from pc- to core-scale in the simulation, which is consistent with the anisotropic core formation model that gas preferably flow along the magnetic field toward dense cores. When comparing the observed cores identified from the GBT Ammonia Survey (GAS) and Planck polarization-inferred magnetic field orientations, we find that the relative core-field alignment has a regional dependence among different clouds. More specifically, we find that dense cores in the Taurus molecular cloud tend to align perpendicular to the background magnetic field, while those in Perseus and Ophiuchus tend to have random (Perseus) or slightly parallel (Ophiuchus) orientations with respect to the field. We argue that this feature of relative core-field orientation could be used to probe the relative significance of the magnetic field within the cloud.

João Alves, Catherine Zucker, Alyssa A. Goodman, Joshua S. Speagle, Stefan Meingast, Thomas Robitaille, Douglas P. Finkbeiner, Edward F. Schlafly, and Gregory M. Green. 2020. “A Galactic-Scale Gas Wave in the Solar Neighbourhood.” Nature, 578, Pp. 237–239. Publisher's VersionAbstract
For the past 150 years, the prevailing view of the local interstellar medium has been based on a peculiarity known as the Gould Belt1-4, an expanding ring of young stars, gas and dust, tilted about 20 degrees to the Galactic plane. However, the physical relationship between local gas clouds has remained unknown because the accuracy in distance measurements to such clouds is of the same order as, or larger than, their sizes5-7. With the advent of large photometric surveys8 and the astrometric survey9, this situation has changed10. Here we reveal the three- dimensional structure of all local cloud complexes. We find a narrow and coherent 2.7-kiloparsec arrangement of dense gas in the solar neighbourhood that contains many of the clouds thought to be associated with the Gould Belt. This finding is inconsistent with the notion that these clouds are part of a ring, bringing the Gould Belt model into question. The structure comprises the majority of nearby star-forming regions, has an aspect ratio of about 1:20 and contains about three million solar masses of gas. Remarkably, this structure appears to be undulating, and its three-dimensional shape is well described by a damped sinusoidal wave on the plane of the Milky Way with an average period of about 2 kiloparsecs and a maximum amplitude of about 160 parsecs.
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Professors Offer Insights From Their Fields Amid COVID

July 10, 2020

In this time of profound uncertainty, society can be sure of one thing: more uncertainty. The seemingly opaque path forward for us, individually and collectively, was the Gazette’s topic with three Harvard professors, including Robert Wheeler Willson Professor of Applied Astronomy, Dr. Alyssa Goodman, who shared insights into how uncertainty is viewed in their fields, and the surprising ways in which it’s not necessarily a bad thing. ...

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Radcliffe Fellow Dr. João Alves On Discovering the "Radcliffe Wave"

June 30, 2020

Astronomer João Alves came to the Radcliffe Institute for Advanced Study to create a 3D map of the sky, but what he discovered overturned the common conception of how stars are born and compelled scientists to rethink the framework of the galaxy.

A professor of stellar astrophysics at the University of Vienna, Alves focuses on understanding how natural processes change large interplanetary clouds of gas into stars and planets, and ultimately form life. He chose to pursue his research at Radcliffe because of its creative, multidisciplinary approach to collaboration. ...

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New Perspectives on Star Formation, the Milky Way, and Isaac Newton, at University of Connecticut, Storrs, CT, Friday, January 17, 2020:

slide screenshotThese are Alyssa Goodman's presentation slides from the 6th annual New England Star Formation Meeting, held at the University Connecticut on January 18, 2020.

These are Alyssa Goodman's presentation slides from the 6th annual New England Star...

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American Astronomical Society Announces First Class of AAS Fellows

February 27, 2020

The American Astronomical Society (AAS) has established a new accolade, Fellow of the AAS, to honor members for extraordinary achievement and service. AAS Fellows will be recognized for original research and publication, innovative contributions to astronomical techniques or instrumentation, significant contributions to education and public outreach, and noteworthy service to astronomy and to the Society itself.

An ...

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The Racliffe Wave

Largest Gaseous Structure Ever Seen In Our Galaxy Is Discovered

January 7, 2020

Astronomers at Harvard University have discovered a monolithic, wave-shaped gaseous structure — the largest ever seen in our galaxy — made up of interconnected stellar nurseries. Dubbed the “Radcliffe Wave” in honor of the collaboration’s home base, the Radcliffe Institute for Advanced Study, the discovery transforms a 150-year-old vision of nearby stellar nurseries as an expanding ring into one featuring an undulating, star-forming filament that reaches trillions of...

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