Cassiopeia Newsletter – Autumnal Equinox 2016
- reneehlozek
- Sep 20, 2016
- 23 min read
Updated: Aug 22, 2025
Date: September 21, 2016
In this Issue:
ALMA Matters
BRITE-Constellation News
CSA
JCMT Update
MSE Update
NRC Herzberg News
SKA Update
News: Canadians become members of the Euclid Consortium
News: Celebrating the history of radio astronomy in Canada
Dissertation: Behaviour of Low-mass X-ray Binaries and their Formation in Globular Clusters
Dissertation: What Governs Star Formation in Galaxies? A Modern Statistical Approach
Dissertation: Monitoring Broad Absorption-line Quasar Variability
Dissertation: X-ray Populations in The Local Group: Insights with Hubble and Chandra
Editor: Magdalen Normandeau & Joanne Rosvick
Cassiopeia is CASCA’s quarterly Newsletter, published on or near the solstices and equinoxes (March 21, June 21, September 21 and December 21).
To submit a contribution please email cassiopeia.editors@gmail.com. All submissions must be received by the due date (usually 2 weeks in advance of publication) to be published in the next edition. I accept plain text and Word documents. Note that the formatting of your document will not be preserved. Please include any images as attachments in your email, not embedded in the text. Please include URLs in parentheses next to the word or phrase that you wish to act as link anchors.
ALMA Matters
From Gerald Schieven (Cassiopeia – Autumn 2016)
Cycle 4 Observing Begins October 1
Since the last issue of this newsletter, the results for the Cycle 4 call for proposals were released. Of the 1571 submitted proposals, 31 had PIs from Canadian institutions, and 153 had some Canadian participation. Of these, 9 proposals with Canadian PIs were awarded time (grade A, B or C) requesting 92 hours, or 5.2% of the time allocated to the North American queue. Cycle 4 observations will begin October 1.
Two Canadian ALMA Development Studies Funded
To maintain ALMA on the forefront of science in the long term, the ALMA Observatory through its Regional Centers provides funding to explore and develop new ideas, techniques, and technology that may have substantial impact on the science capabilities of the facility. Recently six North American projects were granted Development Study funding, among them two projects led by Canadians. The full list of projects can be viewed in the August NRAO e-News. NRAO expects to issue a new Call for Proposals for Development Projects on 10 October 2016. Please see the September NRAO e-News for further information. The deadline for proposals will be at the end of January 2017.
“Cleaning Up Interactive Cleaning” (Rosolowsky (UAlberta), & Kern (NRAO))
The ALMA Development Program is supporting a Study in “Cleaning up Interactive Cleaning” for the CASA software package, led by Erik Rosolowsky (U. Alberta). In many cases, the results from ALMA imaging can be significantly improved by defining regions which contain emission in the deconvolution process. This project will develop a new GUI tool to manage supervised deconvolution, which will enable it to be used in large ALMA data sets. The tool will be built in the new CARTA image viewer, allowing the new viewer to have the same set of functionality as the current CASA viewer.
“Prototype of a Complete Dual-Linear 2SB Block and a Single-Polarization Balanced 2SB Block” (Henke, Naranjanan, & Knee (NRC-HAA))
As part of the Cycle 4 ALMA Development study, we will explore the feasibility of integrating the OMT into the sideband-separating (2SB) waveguide block. We propose to machine and test two prototypes: (1) a dual-linear polarization 2SB block assembly, and, (2) a single polarization balanced 2SB block assembly. Prototype #1 will be used to explore possible improvements in image rejection, narrowband noise temperature, and integration. Prototype #2 will extend the results further to evaluate the added advantages of a balanced receiver, namely reduced signal reflections and LO sideband noise. Measurements will be completed using a spare ALMA Band 3 receiver cartridge and test set currently available at NRC Herzberg. Each prototype piece uses a turnstile as the first element which integrates the OMT into the block and provides the initial power division required for sideband separation. We intend to explore hole couplers as an alternative to branch-guide couplers which are used in most ALMA receiver cartridges. Broad-wall hole couplers are very high-quality couplers that are broadband and exhibit high directivity.
BRITE-Constellation News
From Jaymie Matthews, BEST member (Cassiopeia – Autumn 2016)
The mission has matured to the point where it continues in full science operations, several data releases to BRITE target PIs have already taken place, and some data will soon enter the public domain when the 1-year proprietary period expires.
More information about the mission is available on our website. General inquiries about BRITE-Constellation should be directed to the BEST Chair, Andrzej Pigulski, Univ. Wroclaw, Poland: pigulski@astro.uni.wroc.pl.
Operations
There are five operating BRITE satellites in the Constellation, collecting data on various sky fields in a coordinated programme to obtain well-sampled, long light curves in two bandpasses. As this issue of Cassiopeia went to press, here was the status of the sky assignments for the BRITE cubesats:
BRITE Toronto (Canada) was collecting red-filter photometry of stars in a field which includes Cygnus and Lyra, with trial observations of the Ara-Scorpius field. There were 31 stars in the Ara-Sco trial, several of which turned out to be interesting variables. In mid-September, BRITE Toronto began monitoring the Ara-Sco field full-time. BRITE Toronto’s performance continues to make it the ‘flagship’ of the BRITE photometric fleet.
UniBRITE (Austria) is monitoring the Cygnus-Lyra field in the red bandpass. The goal is switch it to the Cassiopeia field, but this may present some challenges due to startracker problems when the telescope is pointing in the Cas direction, and possible downlink interruptions due to stormy weather at the ground station in Graz (Austria). BRITE Austria is obtaining blue photometry of the Sagittarius and Cassiopeia fields.
Hevelius (Poland) has obtained beautiful red-filter data on stars in the Sagittarius field. In mid-September, it will switch to the Auriga-Perseus field. The other Polish BRITE satellite, Lem (equipped with a blue filter) was dormant for six weeks due to on-board software problems. At press time, it is collecting data in the Cygnus-Lyra field, but will move to Auriga-Perseus in mid-September to join its Polish twin to enable two-colour photometry of this field.
The BRITE Constellation observing programme from early 2017 through mid-2018 is currently being planned by the BRITE Executive Science Team (BEST).
Conferences, Resources and Social Media
The 2nd BRITE Constellation Science Conference was held at the University of Innsbruck, Austria, during 22 – 26 August 2016. Nearly 60 scientists took part, and there was a chance for them to interact with Austrian amateur astronomers. The Canadian Trade Commissioner from the Embassy in Vienna was one of the officials to open the meeting, and she attended the first two days of scientific sessions. For details on the programmes, you can visit the conference website. The Conference Proceedings will appear in early 2017.
The 3rd BRITE Constellation Science Conference will be hosted in Canada in August 2017. The most likely venue will be a lodge in rural Quebec near Montreal.
There will be a BRITE Spectropolarimetric Workshop in Meudon, France during 14 – 18 Nov.
Work is underway on a Public Data Archive, based in Warsaw, Poland at the Nikolaus Copernicus Astronomical Center.
BRITE Constellation is now on Facebook, at @briteconstellation. There is a mission Wiki (including information on past, current and future fields) at http://brite.craq-astro.ca/.
Update from the Canadian Space Agency
From Denis Laurin, Senior Program Scientist, Space astronomy, Space Exploration development CSA (Cassiopeia – Autumn 2016)
Canadian Space Exploration Workshop – CSEW 2016
The CSA will host a consultation workshop on November 24-25 in downtown Montreal to update the space sciences priorities, looking at opportunities for the next decade and beyond. This includes space astronomy, planetary exploration and space health disciplines. Ideas will be welcomed from the community (academia & industry) to help shape future of Canadian space activities. The workshop is a forum for the current space exploration Topical Teams (described in Cassiopeia March 2016) to present and discuss their interim results.
Participation by a broad representation of the community in space sciences is thus important to ensure that the set of objectives of the Canadian Exploration communities are being fully and accurately captured.
More details are presented on the CSEW webpage. There is no fee to participate, but registration is required. For any questions about the workshop please contact: asc.aces-csew.csa@canada.ca.
JCMT Update
By Chris Wilson (Cassiopeia – Autumn 2016)
This update contains three main points:
an update on current programs at the JCMT, particularly the new large programs;
the endorsement by the Long Range Plan Implementation Committee (LRPIC) of continued university involvement in the JCMT; and
plans for how to continue this university involvement.
(1) Current programs at the JCMT: The past 18 months have been a busy and exciting time for the JCMT. As many of you may know, the operation of the JCMT was taken over by East Asian Observatories (EAO) in March 2015. A consortium of 6 Canadian universities has been contributing a small amount of funding (~2% of the total JCMT operations costs) under a two-year agreement with EAO in return for access to observing time and participation in the new large programs. The JCMT archive also continues to reside at the CADC. A consortium of universities in the U.K. has a similar three-year agreement that contributes roughly 20% of JCMT operations costs.
Since the EAO took over JCMT operations, they have issued a call for Large Programs as well as four regular calls for PI programs and have also completed commissioning of the Canadian built polarimeter on SCUBA-2. There are seven large programs approved and running on the JCMT at the moment, most with substantial Canadian leadership and participation. These programs include a transient search for variable protostars, mapping magnetic fields in star-forming regions (BISTRO), a large survey of dust and gas in nearby galaxies from the H-ATLAS and MaNGA surveys (JINGLE, see Figure 1), and a deep continuum map of high redshift sources in the COSMOS field. Observations have been progressing extremely well in this past year and some of the large programs may have obtained all their data by the end of this calendar year. More details on the current large programs can be found here and in the recent JCMT newsletter.
There will be a JCMT User's Meeting in Nanjing, China February 13-14, 2017. A primary focus of this meeting is to discuss the current Large Programs on the JCMT as well as the potential for new Large Programs that will be included in the 17B call for proposals in March 2017. More information about the User's Meeting is available on the JCMT web page.
(2) Open letter to the LRPIC and their response: After the CASCA meeting this past June in Winnipeg, a group of interested astronomers held a short meeting to discuss the status and future of Canadian submillimetre astronomy. This resulted in an open letter to the LRPIC about our discussions that concluded with three broad principles: the need for continued access to the JCMT beyond the January 2017 end of the current agreement and the intention of individual astronomers to seek the necessary funding; the intent of individual community members to seek to participate in CCAT-p, a planned 6 m telescope on the proposed CCAT site; and the intent of the submillimetre community to defer the question of how to achieve access to a next generation submillimetre telescope to the next LRP process that will begin in 2019. This statement of priorities has been fully endorsed by the LRPIC, who stated “Given the uncertain way forward for the CCAT, we agree that access to the JCMT will remain very important to the community for some time to come, and likely for the rest of the current LRP decade. We applaud the efforts of the Universities who have negotiated the present arrangement, and hope that it will continue to provide access to JCMT. We also support continued Canadian involvement as the CCAT plans evolve.” The full letter and the LRPIC's response are posted in the LRPIC area of the CASCA web site.
(3) Extending Canadian JCMT access beyond January 2017: The current Canadian consortium consists of the universities of Alberta, Lethbridge, McMaster, Waterloo, Western, and Saint Mary's. The initial two year agreement with EAO consisted of a financial contribution of $107,000 (Cdn) per year, with the money contributed by the individual universities and/or individuals in amounts ranging from $5,000 to $30,000 per year. We are exploring a number of options for extending this agreement, including an additional round of cash contributions from individual universities and up to three proposals to the NSERC RTI program to purchase small pieces of equipment for the JCMT. We will also be submitting a request for operations funding to NSERC under the newly announced pilot RTI program for Operations and Maintenance Support for Research Equipment. Continued access to the JCMT by Canadians depends on our success in one or more of these options. If anyone is interested in contributing to these efforts, for example by joining the university consortium, I urge you to get in touch with me as soon as possible.
Maunakea Spectroscopic Explorer (MSE) Update
By Patrick Hall, MSE Advisory Group Member (Cassiopeia – Autumn 2016)
MSE is on course for numerous conceptual design reviews to be conducted in Waimea this coming winter. Conceptual design contracts have been signed for the Enclosure with Empire Dynamic Systems (Port Coquitlam, BC) and for the Telescope Structure with IDOM (Spain).
Meanwhile, scientists and engineers from five Canadian universities, along with industry partners, continue to prepare a CFI application for construction of a prototype high-resolution spectrograph and design and development of integrated observational and operational databases and software.
Detailed Science Case on arXiv
A reminder that the 210-page MSE Detailed Science Case has been finalized and published online here. A ten-page concise overview is also available here.
The Detailed Science Case illustrates the breadth of scientific areas in which MSE will have a transformative impact. Detailed Science Case white papers and other background science and technical documents are now posted here.
NRC Herzberg News
From Dennis Crabtree (NRC-Herzberg)(Cassiopeia – Autumn 2016)
These reports will appear in each issue of Cassiopeia with the goal of informing the Canadian astronomical community on the activities at NRC Herzberg.
Feedback is welcome from community members about how NRC Herzberg is doing in fulfilling our mandate to “operate and administer any astronomical observatories established or maintained by the Government of Canada” (NRC Act).
Friends of the DAO
On May 13 of this year NRC signed a License To Occupy (LTO) with the Friends of the DAO Society (FDAO) for use of the Centre of the Universe building. As mentioned in the September, 2016 E-Cass, the FDAO’s main purposes are to “promote interest and awareness of the DAO” and to restart the public education and outreach activities previously provided by the Centre of the Universe. A second LTO was signed providing limited access to the Plaskett Telescope for their outreach activities.
These two agreements are an important step for the FDAO in their public outreach efforts.
Saturday Night Star Parties
The Victoria chapter of the Royal Astronomical Society of Canada (RASC) had a very successful season of Saturday night Star Parties at the DAO. The tradition of opening the DAO’s 1.8-m telescope to the public dates back to the official opening of the telescope in 1918. These events are very popular and this year the RASC instituted a ticketing system (no charge) to alleviate congestion problems at the entrance to DAO at the beginning of the evening. This season, the RASC hosted 13 events (May – August) and had 2222 visitors. Visitors enjoyed viewing through amateur telescopes, public lectures, planetarium shows and viewing through the Plaskett telescope.
Lieutenant Governor of British Columbia
The Honourable Judith Guichon, Lieutenant Governor of British Columbia, paid two visits to the DAO in August. On August 10, Her Honour visited the offices and labs of the DAO. Her Honour was given a presentation on the formation of the DAO, highlighting the provincial contributions, and an overview of NRC Herzberg’s current activities. Following the presentations, Her Honour was given a tour of the laboratories and machine shop.
Her Honour returned for the RASC Saturday night Star Party on August 13. She spent a couple of hours enjoying the events available on Saturday evenings.
SKA Update
By Bryan Gaensler, Canadian SKA Science Director
(Cassiopeia – Autumn 2016)
For more information on the SKA, subscribe to the Canadian SKA email list, and visit the Canadian SKA WWW site.
SKA Science and Science Engagement
An SKA lunch event was held in June 2016 at the CASCA annual meeting in Winnipeg. Speakers were Gary Davis (SKA overview), Séverin Gaudet (Canadian technology activities) and Bryan Gaensler on behalf of Stefi Baum (SKA pathfinder science), with significant time for questions and discussions. Copies of the presentations made at this session are available here.
The SKA project maintains 11 international science working groups and another 2 focus groups. Membership of science working groups and focus groups is open to all qualified astronomers. If you are interested in joining one of these groups, please contact Bryan Gaensler.
The Murchison Widefield Array (MWA) is the precursor of SKA-Low. Construction for MWA phase 2, which will improve the sensitivity of the array by an order of magnitude, is now nearing completion. Canada is now a member of the MWA project, with representation from the University of Toronto on the MWA Board. Any Canadian astronomers wishing to join the MWA Consortium and to consequently gain access to MWA data, software tools and science collaborations should contact Bryan Gaensler.
The main outcome from the ACURA-funded “Canada and the SKA” meeting (held in Toronto in December 2015) was the decision to begin developing the tools and infrastructure needed to support a Canadian SKA Regional Centre. The platform for this is being laid via a funding proposal to the 2017 round of the CFI Innovation program. The proposal, entitled “Unlocking the Radio Sky with Next-Generation Survey Astronomy”, is a partnership between U. Toronto (lead), U. Alberta, UBC, U. Manitoba, Queen’s U. and McGill U. The proposal’s total budget is $9M, which will be used to derive and archive advanced data products for major new surveys with the VLA, CHIME and ASKAP.
SKA Technology Development
NRC Herzberg continues to be a major participant in pre-construction efforts across several of the SKA design consortia. Canada’s main contribution to SKA is in leadership of the Central Signal Processor (CSP) consortium. The down-select process for CSP has taken place, and the package is now proceeding into final design. As previously reported, NRC is no longer designing the reflectors for SKA1-Mid, and is also not pursuing the option to design the sub-reflectors. NRC will be contributing the digitisers and low-noise amplifiers to SKA1-Mid.
ACURA Advisory Council on the SKA
The Association of Canadian Universities for Research in Astronomy (ACURA) coordinates activities and discussion on the SKA through the ACURA Advisory Council on the SKA (AACS); see here for a listing of AACS membership. AACS meets several times per year, with its next meeting on December 12, 2016. For further information or to propose AACS agenda items, please contact the AACS Chair, Bryan Gaensler.
International SKA Activities
Canada is one of 10 member countries of the SKA Organisation, and is represented on the SKA Board of Directors by Greg Fahlman (NRC) and Bryan Gaensler (University of Toronto). The Board most recently met in April 2016 (Cape Town) and July 2016 (Jodrell Bank). Notable outcomes from these two meetings included:
Finalisation of SKA policies on equity and diversity, and of an SKA code of conduct.
Revision and expansion of membership of the SKA Science and Engineering Advisory Committee (SEAC).
Discussion of costing, construction plans and operations plans, with the aim of having construction approval in Dec 2018.
Adoption of the recommendations of the SKA Data Flow Advisory Panel, including establishment of an SKA Regional Centre Coordination Group.
Finalisation of the technical annex to the SKA Observatory Convention (i.e., the text that actually describes the SKA).
Approval of an SKA Engagement Strategy for engagement of new partners and organisations.
Approval of a global SKA Communications Strategy for the next 2 years.
Approval of an SKA Spectrum Management Policy.
Ongoing overviews of the SKA Headquarters and Site Hosting agreements, and of the design and construction of the SKA Headquarters.
Assessment of the SKA Management team.
Establishment of an SKA Management Review Panel, and adoption of this panel’s recommendations.
Election of Bryan Gaensler as science representative to the SKA Board Executive Committee.
The next SKA Board meeting will be held on November 24-25, 2016 (Jodrell Bank).
The SKA Board has recently endorsed the concept of SKA Regional Centres (SRCs) as its preferred model for meeting and managing the challenges posed by the extremely high data rates, data volumes and data analysis requirements of SKA Phase 1. Currently, the project is limited to the basic data products created by the Science Data Processor, stored locally in data processing facilities in the host countries. The scientific success of the SKA is dependent on a viable data management plan for the long-term (50+ years) curation and exploitation of the data products and the infrastructure necessary to achieve this.
The SKA Office has now established an SKA Regional Centre Coordination Group (SRCCG), with responsibilities that include defining a minimum set of requirements for individual SRCs, developing an accreditation process for the SRCS, developing a process to ensure that software tools are interoperable across the SRC network, and investigating models for the future governance of the collaborative network of SRCs. Séverin Gaudet has been appointed as the Canadian representative on the SRCCG.
The annual international SKA Engineering and SKA Science meetings will both be held in the coming months. The SKA Engineering meeting (“Towards Construction”) will take place over October 1-6, 2016, in Stellenbosch, while the SKA Science meeting (“Science for the SKA Generation”) will take place over November 7-11, 2016, in Goa. See https://www.skatelescope.org/events/ for more information.
The University of Toronto and the University of Cape Town will jointly host a major conference, “Fundamental Physics with the Square Kilometre Array”, over May 1-5, 2017,in Mauritius. The goal is to attract the theoretical physics community to the SKA project. See http://www.skatelescope.ca/physics for further details.
For further information on international SKA activities, see the latest SKA Newsletter and the bi-monthly SKA Organisation Bulletin.
SKA Intergovernmental Organisation (IGO) Progress
Negotiations to form an intergovernmental treaty organisation (IGO) to replace the current SKA Organisation are ongoing. Negotiation meetings have taken place in Rome in October 2015, January 2016 and April 2016, and a final meeting is scheduled for September 27-29, 2016. Canada has not participated in these negotiations, but Gilles Joncas (ACURA) and Greg Fahlman / Sean Dougherty (NRC) have attended the first three meetings as observers.
After the final negotiation meeting, the intent is that the convention be “initialed” and sent back to the respective governments for their internal ratification processes. Ratification by five parties, including the three host countries (UK, Australia, South Africa), is required to bring the SKA IGO into existence. This is anticipated to happen by early 2018 in order to initiate procurement activities for the subsequent SKA construction phase.
The principle issues for the Canadian observers are to ensure scientific access to the facility, with opportunities to influence science priorities and to protect the substantial investment made in developing technology that would be applicable to the SKA. The SKA negotiating parties are aware of Canada’s position and conscious of the need to provide alternatives for countries unable to sign the Treaty to maintain engagement in the project.
News: Canadians become members of the Euclid Consortium
By Ray Carlberg
(Cassiopeia – Autumn 2016)
Recently CFHT approved the Canada-France Imaging Survey as a Large Program for 271 nights. The Canadian PI is Alan McConnachie, and Rodrigo Ibata for France. The survey will give slightly deeper than u~24 and r~24 imaging over a (highly approximate) 10,000 and 5,000 square degrees, respectively. CFIS has a range of standalone science goals. As announced in a CASCA email in July, the Euclid Consortium offered a number of memberships in return for access to the data. Euclid is a ESA mission to measure the geometry of the universe and test gravitation theory on large scales using a combination of photometric measurements of clustering, infall velocities from low resolution spectra, and weak gravitational lensing measurements. The satellite will provide a large legacy dataset in the YJH bands, at roughly 0.3” resolution, and a wide visible (riz) band, at 0.1” resolution. The Euclid survey area is approximately 15,000 square degrees of high galactic latitude sky. The mission is described at http://sci.esa.int/euclid/.
Euclid is of interest from other telescopes. On the ground a Spanish telescope will cover the northern (CFIS) area in the g band and there is interest from Subaru in doing some redder bands. Spitzer recently approved 5286 hours for the Euclid/WFIRST Spitzer Legacy Survey (PI: Peter Capak, a Canadian).
Euclid has approved membership for the following people: Michael Balogh, Dick Bond, Jo Bovy, Raymond Carlberg, Scott Chapman, Patrick Cote, Nicolas Cowan, Sebastien Fabbro, Laura Ferrarese, Renee Hlozek, Mike Hudson, JJ Kavelaars, Dustin Lang, Alan McConnachie, Adam Muzzin, Laura Parker, Chris Pritchet, Marcin Sawicki, David Schade, Douglas Scott, Kendrick Smith, Kristine Spekkens, James Taylor, Chris Willott. John Hutchings and Denis Laurin are ex officio members for CSA. Carlberg will be the initial ECB member for Canada and is the contact point in Canada for Euclid matters. It has been a somewhat winding road to participation in this important mission. Although CSA helped start the process it needed to step away a few years ago. No direct funding is attached to our participation, although the obligation to provide the data is of interest to CADC/CANFAR. As resignations occur new memberships may become available in the future.
Celebrating the History of Radio Astronomy in Canada
By Tim Robishaw, DRAO (Cassiopeia – Autumn 2016)
A workshop on the history of Canadian radio astronomy was held July 25 and 26 at the Dominion Radio Astrophysical Observatory (DRAO).
Workshop participants under the John A. Galt 26-m telescope.
A major motivation for the event was the work of the late Richard Jarrell (York University), the author of “The Cold Light of Dawn: A History of Canadian Astronomy”. Richard collected an extensive archive on the history of Canadian radio astronomy, including many interviews with all the original players. Richard had just begun writing a book on this topic at the time of his passing in late 2013. A group of Canadian radio astronomers hopes to finish writing this book following the outline Richard provided and using his archival material. To this end, in addition to topics of worldwide importance to the history of radio astronomy, contributions were solicited on topics pertaining to the development of radio astronomy in Canada. Richard’s wife, Martha, attended the workshop and hand-delivered Richard’s archives and interviews to DRAO where they will be housed.
The workshop included 27 talks covering a breadth of stories about the development of radio astronomy at Canada’s universities and observatories. The nearly 50 attendees took part in a discussion about practicing history led by Woody Sullivan (University of Washington), Miller Goss (NRAO)—both active historians of radio astronomy—and NRAO Archivist, Ellen Bouton.
A website containing videos of the talks and photos from the workshop can be found here. And thanks to Joseph Fletcher (NRC, retired) and Bob Hayward (NRAO, retired), we now have video of a 1987 NRC workshop entitled “Radio Astronomy and Canada: Fifty Years of Progress”. These videos can also be found at the above website.If you prefer to view the videos directly, the Youtube links to the workshop playlists are below:
Dissertation: Behavior of Low-mass X-ray Binaries and their Formation in Globular Clusters
(Cassiopeia – Autumn 2016)
by Arash Bahramian
Thesis defended on June 22, 2016
Department of Physics, University of Alberta
Thesis advisor: Dr. Craig O. Heinke
Abstract:
Low mass X-ray binaries (LMXBs) are systems of compact stellar remnants accreting from a low mass companion star. These systems show various levels of mass transfer on various timescales. Many aspects of accretion in these systems are still not fully understood, specifically the emission processes involved in various states of mass transfer. The population of LMXBs has been found to be orders of magnitude higher (per unit mass) in globular clusters (GCs) compared to the Galactic field. This overabundance has been explained as due to the formation of LMXBs by stellar encounters in GCs. In this thesis, we study GC LMXB populations, and the details of accretion in these systems. First, we focus on the population of LMXBs and the role of stellar encounters in their formation in GCs. We calculate model-independent stellar encounter rates for 124 Galactic GCs, and show that core-collapsed clusters tend to have lower numbers of LMXBs compared to other clusters with similar values of the stellar encounter rate. Then, we focus on studying accretion in LMXBs in various classes of systems (quiescent, transient, ultra-compact and symbiotic). We provide evidence for the presence of low-level accretion in the rise and decay of outbursts in transient LMXBs, and the absence of low-level accretion in many quiescent neutron star LMXBs. Finally we study two peculiar LMXBs, and show that one is an ultra-compact X-ray binary, and another one is a symbiotic X-ray binary.
Dissertation: What Governs Star Formation in Galaxies? A Modern Statistical Approach
(Cassiopeia – Autumn 2016)
By Sahar Rahmani
Thesis defended on August 23, 2016
Department of Physics and Astronomy, Western University
Thesis advisor: Dr. Pauline Barmby
Abstract:
Understanding the process of star formation is one of the key steps in understanding the formation and evolution of galaxies. In this thesis, I address the empirical star formation laws, and study the properties of galaxies that can affect the star formation rate.
The Andromeda galaxy (M31) is the nearest large spiral galaxy, and therefore, high resolution images of this galaxy are available. These images provide data from various regions with different physical properties. Star formation rate and gas mass surface densities of M31 have been measured using three different methods, and have been used to compare different star formation laws over the whole galaxy and in spatially-resolved regions. Using hierarchical Bayesian regression analysis, I conclude that there is a correlation between surface density of star formation and the stellar mass surface density. A weak correlation between star formation rate, stellar mass and metallicity is also found.
To study the effect of other properties of a galaxy on the star formation rate, I utilize an unsupervised data mining method (specifically the self-organizing map) on measurements of both nearby and high-redshift galaxies.Both observed data and derived quantities (e.g. star formation rate, stellar mass) of star-forming regions in M31 and the nearby spiral galaxy M101 are used as inputs to the self-organizing map. Clustering the M31 regions in the feature space reveals some (anti)-correlations between the properties of the galaxy, which are not apparent when considering data from all regions in the galaxy. The self-organizing map can be used to predict star formation rates for spatially-resolved regions in galaxies using other properties of those regions.
I also apply the self-organizing map method to spectral energy distributions of high-redshift galaxies. Template spectra made from galaxies with known morphological type are used to train self-organizing maps. The trained maps are used to classify a sample of galaxy spectral energy distributions derived from fitting models to photometry data of 142 high-redshift galaxies. The grouped properties of the classified galaxies are found to be more tightly correlated in mean values of age, specific star formation rate, stellar mass, and far-UV extinction than in previous studies.
Dissertation: Monitoring Broad Absorption-line Quasar Variability
(Cassiopeia – Autumn 2016)
By Jesse Rogerson
Thesis defended on April 18, 2016
Department of Physics and Astronomy, York University
Thesis advisor: Dr. Patrick Hall
Abstract:
Winds generated by an accreting super massive black hole may provide feedback to the host galaxy and offer an explanation for the co-evolution of galaxies with their super massive black holes that has been reported in the literature. Some outflows are manifested as broad absorption line (BAL) troughs in quasar spectra, and are measured at velocities as high as ~60,000 km s−1 at ultra-violet wavelengths. These BAL troughs have been observed to vary on both long (years) and short (weeks) rest-frame time-scales and can emerge in a quasar that had none, or disappear completely. By monitoring the variability of absorption in BAL quasars, constraints can be placed on outflow models and the structure of quasars in general.
In this study, we isolate a set of quasars that exhibit emergent CIV BALs in their spectra, by comparing archival data in the SDSS Data Release 7 to the BOSS Data Release 9 and 10. After visually defining a set of emergent BALs, follow-up observations were obtained with the Gemini Observatory for 105 quasars. BALs were formally detected in all but two of the quasars in the dataset, and we report 219 absorption complexes in the entire set. After a BAL has emerged, we find it is equally likely to continue increasing as it is to start decreasing in a subsequent observation. Based on the range of time between our observations, this indicates the coherence time-scale of BALs is less than 100 days. There is a strong signal of coordinated variability among two troughs in the same quasar. Further, coordination is stronger if the velocity separation between the two troughs is smaller. We conclude the variability is likely due to changes in the ionizing flux incident on the absorbing cloud, which agrees with the results of Filiz Ak et al. (2013).
In this work we also test two competing models of BAL variability (bulk motion and ionization changes) in the context of a case study of the quasar SDSS J023011.28+005913.6, which had two high-velocity emergent troughs. Both models yield plausible results.
Dissertation: X-ray Populations in The Local Group: Insights with Hubble and Chandra
(Cassiopeia – Autumn 2016)
By Neven Vulic
Thesis defended on June 21, 2016
University of Maryland, College Park
Thesis advisors: Dr. Pauline Barmby and Dr. Sarah C. Gallagher
Abstract:
X-ray observations provide a unique perspective on the most energetic processes in the Universe. In particular, Low-mass X-ray binaries (LMXBs) found in globular clusters have been shown to depend on the mass, radius, and metallicity of the cluster. This thesis focuses on the impact environmental parameters have on X-ray sources and the underlying physical explanations for them. I studied the X-ray binary population in M31 using 1 Ms of Chandra ACIS data and 6-filter photometry from the Panchromatic Hubble Andromeda Treasury Survey. From a sample of 83 star clusters we found the brightest and most compact star clusters preferentially hosted an X-ray source. An investigation of 1566 H II regions found that neither radius nor H-alpha luminosity was a predictor of an H II region hosting an X-ray source. To study the faintest X-ray sources a stacking analysis of star clusters and H II regions was completed. Non-detections throughout resulted in upper limits of ~10×1032 erg/s. I produced the most sensitive Chandra X-ray point source catalogue of M31, detecting 795 X-ray sources in an area of ~0.6 deg2, to a limiting unabsorbed 0.5-8.0 keV luminosity of ~10×1034 erg/s. The flatter completeness-corrected X-ray luminosity function of the bulge compared to the disk, consistent with previous work, indicated a lack of bright high-mass X-ray binaries in the disk and an aging population of LMXBs in the bulge. I also investigated the origin of the relationship between the metallicity of 109 Galactic globular clusters and LMXB formation by studying the number density of red giant branch (RGB) stars. A Spearman Rank test between the RGB star density and metallicity [Fe/H] confirmed the data could not have been drawn from a random distribution.
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