X-Shooter observations of low-mass stars in the Eta Chamaeleontis association

The nearby Eta Chamaeleontis association is a collection of 4-10 Myr old stars with a disk fraction of 35-45%. In this study, the broad wavelength coverage of VLT/X-Shooter is used to measure the stellar and mass accretion properties of 15 low mass stars in the Eta Chamaeleontis association. For each star, the observed spectrum is fitted with a non-accreting stellar template and an accretion spectrum obtained from assuming a plane-parallel hydrogen slab. Five of the eight stars with an IR disk excess show excess UV emission, indicating ongoing accretion. The accretion rates measured here are similar to those obtained from previous measurements of excess UV emission, but tend to be higher than past measurements from H-alpha modeling. The mass accretion rates are consistent with those of other young star forming regions.Comment: Accepted for publication in Astronomy & Astrophysic

On the formation and destruction of molecular clouds with the Galactic plane survey THOR

This thesis investigates the properties of molecular clouds with THOR (The HI, OH and Radio Recombination Line (RRL) survey of the Milky Way). We analyze OH absorption at 18 cm within THOR and follow-up observations. We derive the abundance with respect to molecular hydrogen and the total number of hydrogen nuclei: 1) We find a decreasing OH abundance with increasing column density of molecular hydrogen. 2) Due to significant column densities of atomic hydrogen at low N_OH, the OH abundance with respect to N_H is approximately constant. 3) We detect OH components which are associated with gas that is not predominantly molecular or even CO-dark. We conclude that OH is a potential tracer for diffuse gas. Regarding the impact of star clusters on molecular clouds, we detect signatures of feedback in RRL emission in the star forming region W49A. A comparison to the WARPFIELD models (one-dimensional models of feedback-driven shells) indicates that feedback is not yet strong enough to disperse its molecular cloud and that the shell is either in process of re-collapsing to initiate a new event of star formation or has already re-collapsed. This suggests that at least parts of the star formation in W49A is regulated by feedback

Confirmation Of Two Galactic Supernova Remnant Candidates Discovered By THOR

Anderson et al. (2017) identified seventy six candidate supernova remnants (SNRs) using data from The HI, OH, Recombination line survey of the Milky Way (THOR). The spectral index and polarization properties can help distinguish between SNRs and H II regions, which are often confused. We confirm two SNR candidates using spectral index data and morphology. However, we observe that the fractional linear polarization cannot distinguish between SNRs and H II regions, likely due to contamination by diffuse Galactic synchrotron emission. We also comment on the association of SNR candidates with pulsars through geometric and age considerations.Comment: 12 pages, 4 figures; Accepted for publication in Ap

Metrewave Galactic Plane with the uGMRT (MeGaPluG) Survey: Lessons from the Pilot Study

Context. The advent of wide-band receiver systems on interferometer arrays enables one to undertake high-sensitivity and high-resolution radio continuum surveys of the Galactic plane in a reasonable amount of telescope time. However, to date, there are only a few such studies of the first quadrant of the Milky Way that have been carried out at frequencies below 1 GHz. The Giant Metrewave Radio Telescope (GMRT) has recently upgraded its receivers with wide-band capabilities (now called the uGMRT) and provides a good opportunity to conduct high resolution surveys, while also being sensitive to the extended structures. Aims. We wish to assess the feasibility of conducting a large-scale snapshot survey, the Metrewave Galactic Plane with the uGMRT Survey (MeGaPluG), to simultaneously map extended sources and compact objects at an angular resolution lower than $10''$ and a point source sensitivity of 0.15 mJy/beam. Methods. We performed an unbiased survey of a small portion of the Galactic plane, covering the W43/W44 regions ($l=29^\circ-35^\circ$ and $|b|<1^\circ$) in two frequency bands: 300$-$500 MHz and 550$-$750 MHz. The 200 MHz wide-band receivers on the uGMRT are employed to observe the target field in several pointings, spending nearly 14 minutes on each pointing in two separate scans. We developed an automated pipeline for the calibration, and a semi-automated self-calibration procedure is used to image each pointing using multi-scale CLEAN and outlier fields. Results. We produced continuum mosaics of the surveyed region at a final common resolution of $25''$ in the two bands that have central frequencies of 400 MHz and 650 MHz, with a point source sensitivity better than 5 mJy/beam. We plan to cover a larger footprint of the Galactic plane in the near future based on the lessons learnt from this study. (Abridged)Comment: To be published in A&A. 13 pages, 10 figure

Accelerator mass spectrometry measurement of the reaction 35Cl(n,γ)36Cl at keV energies

The nuclide 35Cl can act as a minor “neutron poison” in the stellar slow neutron capture process

A global view on star formation: the GLOSTAR Galactic plane survey III. 6.7 GHz methanol maser survey in Cygnus X

The Cygnus X complex is covered by the Global View of Star Formation in the Milky Way (GLOSTAR) survey, an unbiased radio-wavelength Galactic plane survey, in 4–8 GHz continuum radiation and several spectral lines. The GLOSTAR survey observed the 6.7 GHz transition of methanol (CH$_3$OH), an exclusive tracer of high-mass young stellar objects. Using the Very Large Array in both the B and D configurations, we observed an area in Cygnus X of 7° × 3° in size and simultaneously covered the methanol line and the continuum, allowing cross-registration. We detected thirteen sources with Class II methanol maser emission and one source with methanol absorption. Two methanol maser sources are newly detected; in addition, we found four new velocity components associated with known masers. Five masers are concentrated in the DR21 ridge and W75N. We determined the characteristics of the detected masers and investigated the association with infrared, (sub)millimeter, and radio continuum emission. All maser sources are associated with (sub)millimeter dust continuum emission, which is consistent with the picture of masers tracing regions in an active stage of star formation. On the other hand, only five masers (38 ± 17%) have radio continuum counterparts seen with GLOSTAR within ~1″, testifying to their youth. Comparing the distributions of the bolometric luminosity and the luminosity-to-mass ratio of cores that host 6.7 GHz methanol masers with those of the full core population, we identified lower limits L$_{Bol}$ ~ 200 L$_⊙$ and L$_{Bol}$/M$_{core}$ ~ 1 L$_⊙$M$_⊙^{−1}$ for a dust source to host maser emission

The JWST Galactic Center Survey -- A White Paper

The inner hundred parsecs of the Milky Way hosts the nearest supermassive black hole, largest reservoir of dense gas, greatest stellar density, hundreds of massive main and post main sequence stars, and the highest volume density of supernovae in the Galaxy. As the nearest environment in which it is possible to simultaneously observe many of the extreme processes shaping the Universe, it is one of the most well-studied regions in astrophysics. Due to its proximity, we can study the center of our Galaxy on scales down to a few hundred AU, a hundred times better than in similar Local Group galaxies and thousands of times better than in the nearest active galaxies. The Galactic Center (GC) is therefore of outstanding astrophysical interest. However, in spite of intense observational work over the past decades, there are still fundamental things unknown about the GC. JWST has the unique capability to provide us with the necessary, game-changing data. In this White Paper, we advocate for a JWST NIRCam survey that aims at solving central questions, that we have identified as a community: i) the 3D structure and kinematics of gas and stars; ii) ancient star formation and its relation with the overall history of the Milky Way, as well as recent star formation and its implications for the overall energetics of our galaxy's nucleus; and iii) the (non-)universality of star formation and the stellar initial mass function. We advocate for a large-area, multi-epoch, multi-wavelength NIRCam survey of the inner 100\,pc of the Galaxy in the form of a Treasury GO JWST Large Program that is open to the community. We describe how this survey will derive the physical and kinematic properties of ~10,000,000 stars, how this will solve the key unknowns and provide a valuable resource for the community with long-lasting legacy value.Comment: This White Paper will be updated when required (e.g. new authors joining, editing of content). Most recent update: 24 Oct 202

Beyond the Normalized Difference Vegetation Index (NDVI) : Developing a Natural Space Index for population-level health research

Background: Natural spaces can provide psychological benefits to individuals, but population-level epidemiologic studies have produced conflicting results. Refining current exposure-assessment methods is necessary to advance our understanding of population health and to guide the design of health-promoting urban forms. Objectives: The aim of this study was to develop a comprehensive Natural Space Index that robustly models potential exposure based on the presence, form, accessibility, and quality of multiple forms of greenspace (e.g., parks and street trees) and bluespace (e.g., oceans and lakes). Material and methods: The index was developed for greater Vancouver, Canada. Greenness presence was derived from remote sensing (NDVI/EVI); forms were extracted from municipal and private databases; and accessibility was based on restrictions such as private ownership. Quality appraisals were conducted for 200 randomly sampled parks using the Public Open Space Desktop Appraisal Tool (POSDAT). Integrating these measures in GIS, exposure was assessed for 60,242 postal codes using 100- to 1,600-meter buffers based on hypothesized pathways to mental health. A single index was then derived using principal component analysis (PCA). Results: Comparing NDVI with alternate approaches for assessing natural space resulted in widely divergent results, with quintile rankings shifting for 22-88% of postal codes, depending on the measure. Overall park quality was fairly low (mean of 15 on a scale of 0-45), with no significant difference seen by neighborhood-level household income. The final PCA identified three main sets of variables, with the first two components explaining 68% of the total variance. The first component was dominated by the percentages of public and private greenspace and bluespace and public greenspace within 250 meters, while the second component was driven by lack of access to bluespace within 1 kilometer. Conclusions: Many current approaches to modeling natural space may misclassify exposures and have limited specificity. The Natural Space Index represents a novel approach at a regional scale with application to urban planning and policy-making.Arts, Faculty ofMedicine, Faculty ofPopulation and Public Health (SPPH), School ofSocial Work, School ofReviewedFacult

Exposure to natural space, sense of community belonging, and adverse mental health outcomes across an urban region

In a rapidly urbanizing world, identifying evidence-based strategies to support healthy design is essential. Although urban living offers increased access to critical resources and can help to mitigate climate change, densely populated neighborhood environments are often higher in many of the physical and psychological stressors that are detrimental to health, and lower in the social capital that is beneficial to health. One component of urban form that can reduce these stressors and improve social capital is nature: greenspace, such as parks and street trees, and bluespace, such as rivers and oceans. In this project, we applied measures from a Natural Space Index previously developed for the Vancouver, Canada census metropolitan area to explore the relationship between distinct measures of natural space and prevalence of (1) major depressive disorder, (2) negative mental health, and (3) psychological distress. In addition, we examined direct associations between natural space exposure and neighborhood social capital, as measured via self-reported sense of community belonging (SoC), as well as the potential mental health benefits of natural space mediated via SoC. Using data from the population-based, cross-sectional 2012 Canadian Community Health Survey-Mental Health (weighted n=1,930,048), we found no direct associations between any measure of natural space and mental health in models adjusted for 11 demographic, socioeconomic, household arrangement, health, and urban design variables. However, publicly accessible neighborhood nature was associated with increased odds of higher SoC. A 1% increase in the percentage of natural space (combined greenspace and bluespace) within 500m had an odds ratio [95% confidence interval] of 1.05 [1.00, 1.10] for very strong vs. very weak SoC and 1.04 [1.01, 1.08] for somewhat strong vs. very weak SoC. In addition, higher levels of SoC were associated with improvements in all three mental health outcomes. Mediation tests indicated significant indirect effects of both publicly accessible neighborhood nature variables on reductions in psychological distress and reduced odds of negative mental health via increased sense of SoC. This suggests that natural space has the potential to address the pressing issue of social isolation and, in turn, poor mental health faced by residents of dense urban environments.Medicine, Faculty ofNon UBCPopulation and Public Health (SPPH), School ofReviewedFacult