Category Archives: News and Announcements

By Doug Johnstone, Associate Director JCMT

Countdown! September has arrived and I am now in the last month of my secondment to the Joint Astronomy Centre as Associate Director JCMT. It is hard to believe that two years have passed so very quickly, and of course, there still seems to be a great deal left to accomplish before the end of the month, including this Newsletter piece.

As usual, in this update I will describe recent events at the JCMT, including progress within the JCMT Legacy Surveys, a recap of Semester 14A, and the present status of the JCMT Science Archive. For details on the on-going efforts to transfer the JCMT to an East Asian consortium, please refer to the article in the Summer Solstice edition (June 2014) on the ‘Continuing Evolution of the JCMT’, by Gary Davis, Director of the JAC.

The showcase science programme at the JCMT remains the JCMT Legacy Survey (JLS), covering debris disks, star formation near and far within our Galaxy, nearby Galaxies, and cosmology. Over the last nine months we have managed to increase the completion fraction of the survey, from about 50% to over 75%, despite a dismal winter for sub-millimetre observing on Maunakea. All six of the SCUBA-2 legacy surveys now have a majority of their observations in hand, with the debris disk survey reaching 100% completion in August. Our recent efforts to streamline the observing process and extend observing into the morning hours through limited remote operations have clearly paid off. Of course it also helps when the nightly fault rate for the telescope drops well below 5% of clear-sky time – an impressive threshold for a twenty-seven year old telescope with complex cryogenic and superconducting instrumentation. Kudos and mahalo to the dedicated JAC staff!

We anticipate that JLS observations will be taken throughout much of the Fall as negotiations continue with the East Asian consortium, soon to be known as the East Asian Observatory (EAO), on the smooth transfer of the telescope. Looking further into the future, it is clear that large legacy surveys will be a continuing tradition at the JCMT, and Canadians are being asked to help define these priorities. A number of us will be taking part in a meeting in the UK near the end of September where new and expanded surveys for the JCMT will be developed. Christine Wilson (McMaster) continues to lead the Canadian effort for continued JCMT involvement beyond the NRC Herzberg era.

As Semester 14A nears conclusion, a bittersweet moment for Canada was reached on Thursday, August 13th with the last night of Canadian observing under NRC Herzberg management. Both JAC Director Gary Davis and I were there to mark the occasion, along with UBC graduate student Todd Mackenzie (see attached photo). Todd’s connection to the JCMT started while an undergraduate student. Working as a co-op student at NRC Herzberg with James Di Francesco and me, he helped produce SCUBA Legacy images and catalogues. Now Todd is using SCUBA-2 data as part of his PhD thesis, under the direction of Douglas Scott. Despite having to note the end of an era, I am pleased to announce that Canadian PI’s did extremely well with their share of the flexible telescope time this last semester. Six of the seven top proposals in the Canadian queue obtained at least 95% of their requested observing time. The outlier proposal was, unfortunately, a target of opportunity that simply did not trigger.

In the 2013 Winter Solstice edition I discussed the importance of the JCMT Science Archive (JSA) as part of the legacy of the JCMT. This effort, a collaboration between the JAC and the CADC at NRC Herzberg in Victoria, has been extremely active over the last year. Regular JSA users will have already noticed the simplified interface through which they now search the archive. For those daunted by this change, a helpful primer on searching the JSA is available on the JAC web-page (follow the link from the JCMT landing page at the CADC). Further JSA effort includes a plan for the uniform reduction and cataloguing of all public JCMT SCUBA-2 data residing in the archive. Initial pipeline processing for this effort is now underway and these legacy data products should start to become available through the archive in late Spring 2015. Together with the individual JCMT Legacy Survey team reductions, which are specially designed to pick out science-goal specific features such as point sources or extended structure, these uniformly reduced data products will provide a lasting legacy for the JAC era at the JCMT.

It feels extremely strange to be saying good-bye to the JCMT at this time. This is especially true given that I have spent the last few months working closely with the Director to help secure a long-term future for the JCMT through its transfer to EAO, espousing my admiration and respect for the telescope, its staff, and its community at every opportunity. Just last week I was in Japan at an NAOJ JCMT workshop and next week I will be in the UK to help design future legacy surveys. It is my great hope that despite my formal departure, I will continue to be intimately involved with the JCMT, both as a scientist, making use of its fantastic instrumentation, and as an advocate, providing support and constructive criticism to the new management. Long live the JCMT.

Todd Mackenzie, Doug Johnstone, and Gary Davis in the JCMT control room on the last night of Canadian observing under NRC management. (Photo Credit: T. McLaughlin)

By Chris Wilson, Canadian ALMA Project Scientist
with material from the NRAO newsletters and the ALMA web site

ALMA Current Status

ALMA construction continues to wind down. In late June, 2014, the final ALMA antenna was taken up to the high-level site 5000 meters above sea level. Its arrival completes the complement of 66 ALMA antennas on the Chajnantor Plateau in the Atacama Desert of northern Chile. Images and video of the antenna move can be found at http://www.almaobservatory.org/

The ALMA Phasing Project team, with support from the Extension and Optimization of Capabilities (EOC) Team, the ALMA Department of Engineering, and the ALMA Department of Computing, integrated the new hydrogen maser into the ALMA system. This is an important milestone toward incorporating ALMA as a Very Long Baseline Interferometry array element. Tests have shown the maser performance is excellent, and it has replaced the rubidium clock as the ALMA time standard.

The August weather at Chajnantor was very good, as is usual for the austral winter, and the high frequency campaign made good use of the resulting excellent high frequency transparency. Multiple objectives were met, including the imaging of Uranus with 29 array elements at ALMA Band 10 (350 microns, 810 GHz) by the EOC team. The EOC team also demonstrated the transfer of phase information from lower frequencies, where calibrators are brighter and more densely distributed, to higher frequencies. Simultaneous sub-arraying within the main 12 m array was demonstrated for the first time, a key goal for achieving simultaneous EOC and Early Science operations.

On September 1, 2014, the EOC Team started the Long Baseline Campaign and will continue commissioning-type observations through the end of November. This critical campaign is essential for Cycle 3 proposed capabilities and will test the calibration and imaging characteristics of ALMA out to baselines of at least 10 km. All ALMA Early Science Observations (both Cycle 2 and carryover Cycle 1 programs) have been halted until the end of the campaign. This break in Early Science observing is needed because of the time required to move antennas out to the largest configurations and the fact that once the antennas are spread out to 5-10 km, the antennas remaining nearer the center of the array are not sufficient to populate any of the Cycle 2 configurations.

ALMA Cycle 2 progress

Results of the Cycle 2 proposal review process were sent to the PI on April 9, 2014 and the full list was released May 2, 2014. A full listing of the 353 highest priority proposals is available here. More recently, a detailed report on the outcome of the ALMA Early Science Cycle 2 Proposal Review Process has become available. The report describes the proposal review process, proposal statistics and regional distributions as well as the proposal distribution across science categories and receiver bands. The report can be downloaded as a pdf document here.

Cycle 2 observing began in a higher resolution configuration, with a longest baseline of 650 m, and is planned to cycle into larger configurations as the austral winter progresses. As noted above, all ALMA Early Science Observations have been halted until the end of the long baseline campaign. Early Science observations are scheduled to resume in December 2014 in array configuration C34-3. Observations in array configuration C34-1 are expected to begin in January 2015.

PIs and Co-Investigators can consult the Project Tracker for information on the execution of an accepted project. PIs can also modify their user profile at the Science Portal to receive e-mail notifications whenever a component of a project is first observed, fully observed, or successfully processed.

Archival and Science Verification Data

All the data from Cycle 0 Early Science projects have been delivered. The data are made publicly available via the ALMA archive as the one-year proprietary period expires. A total of 109 of the 116 Cycle 0 projects are available in the ALMA Science Archive; only a few projects are still within their proprietary period. Twenty-five of the 69 North American high priority Cycle 1 projects have been fully delivered and two-thirds of the highest-ranked NA Cycle 1 projects have seen deliveries of some data.

Data for two new ALMA Science Verification targets were released on September 7, 2014. The targets are (1) the evolved star VY Cma observed in water maser lines in Bands 7 (~850 microns) and 9 (~450 microns) and demonstrating ALMA capabilities on 1-3 km baselines and (2) Comet Lemmon observed in the HCN line in Band 6 (~1.1 mm) and demonstrating Doppler tracking of ephemeris targets. All Science Verification targets are listed on the Science Verification web page and the data sets are available through the ALMA Science Portal.

ALMA software news

CASA release 4.2.2 is now available from the CASA homepage: http://casa.nrao.edu/.This is a patch release of CASA 4.2.0/4.2.1 to introduce SIGMA and WEIGHT columns defined according to channel width and integration time. The patch also adds the plotms capability to export iterated plots in multiple files. A detailed description of the CASA visibility weighting scheme can be found at http://casa.nrao.edu/Memos/CASA-data-weights.pdf. CASA, the Common Astronomy Software Applications (CASA) package, is being developed by NRAO, ESO, and NAOJ and is used for the offline reduction and analysis of both ALMA and VLA data. CASA is fully scriptable. Full support is provided for ALMA and VLA but almost any data that can be written in uvfits format can be imported and reduced in CASA (for example, CARMA, SMA, ATCA).

ALMA has begun routine data reduction using the automated pipeline. The pipeline is now the principle means of data calibration and flagging for PI projects at ALMA. Previously, all ALMA data were reduced manually by ALMA’s team of scientists around the globe. For example, for North American projects the data have been reduced by staff scientists at the North American ALMA Science Center (NAASC) at NRAO Headquarters in Charlottesville and in Victoria, Canada, and at the Joint ALMA Observatory in Santiago, Chile. This transition to pipeline processing comes at a critical time when the ALMA data rate is high and continuing to grow. The pipeline is essential to allowing the ALMA observatory to cope with the current and anticipated future data rates. The pipeline has been developed by a dedicated team of engineers and scientists (including, from 2002-2010, C. Wilson as the sub-system scientist) with the aim of being able to handle the majority of ALMA observing projects. Some non-standard modes will continue to need manual reduction. The pipeline currently handles flagging and calibration while the imaging step continues to be done manually. The imaging portion of the pipeline is still under development and testing.

ALMA Meetings

There are two workshops and one major ALMA meeting planned in the next year:

“Revolution in Astronomy with ALMA: The Third Year” will be held from December 8-11, 2014, in Tokyo, Japan. Registration is still open and the deadline for abstracts for posters and registration is October 15, 2014. The web site is http://www.almasc2014.jp/.

A NAASC workshop on “The Filamentary Structure in Molecular Clouds” is being held 10-11 October 2014 in Charlottesville Virginia. Registration is now closed but there is a waiting list. The conference web site is https://science.nrao.edu/science/meetings/2014/filamentary-structure/.

“Dissecting Galaxies Near and Far” is the subject of a workshop to be held March 23-27, 2015 in Santiago, Chile. Preliminary information is available on the conference web site, http://www.eso.org/sci/meetings/2015/Galaxies2015.html.

Information

A good source for monthly updates on the ALMA project is the electronic NRAO newsletter
http://science.nrao.edu/enews/. And don’t forget the ALMA observatory web site http://www.almaobservatory.org/ which contains wide range of information about the observatory, including details about science and technology, infrastructure, and geographical location.

An email list has been created for Canadian astronomers interested in ALMA. This moderated list will periodically send out updates on ALMA’s status, news of software releases, notices of upcoming ALMA science meetings and workshops, etc., which would be of interest to Canadian astronomers. Those who wish to be subscribe to the alma-users list are encouraged to visit the web page http://lists.astrosci.ca/mailman/listinfo/alma-users/ or send an email to Gerald.Schieven(at)nrc-cnrc.gc.ca.

By Dennis Crabtree, Director Dominion Astrophysical Observatory (acting) & Optical Astronomy Program Leader (acting)
with contributions from Alan McConnachie, James Hesser, Gary Hovey, Gordon Lacy, Kei Szeto

These reports will appear in each issue of E-Cass 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).

Cyber Intrusion at NRC

On 29 July, NRC announced that it had detected and confirmed a cyber intrusion on its IT infrastructure. NRC took steps to protect its information and the information of its clients and stakeholders by isolating its information holdings and shutting down servers including several at NRC Herzberg, that contained sensitive information.

We were able to implement some important workarounds to keep the majority of our services running. NRC Herzberg expects to be able to resume normal activities by the middle of October.

Return of Public Outreach to DAO

Efforts initiated in summer 2013 by community groups bore fruit. Groups distressed by the closure of the public outreach program operated at the Centre of the Universe facility on Observatory Hill worked with NRC to restore some outreach activities for summer 2014. This was spurred by on-line petitions organized by Don Moffatt (an interpreter at DAO in the 1990s) and by MLA Lana Popham, in whose riding the DAO is located. Last November MLA Popham organized at DAO a critical meeting of community representatives, in which NRC VP Dan Wayner participated with Greg Fahlman and Jim Hesser. This created the atmosphere for productive discussions with Observatory and NRC management that ultimately led to two, highly successful, pilot projects to re-introduce astronomy-themed education and public outreach during summer 2014.

NRC facilitated access for the University of Victoria’s Science Venture (SV) program to the Centre of the Universe building for weekly astronomy and space science camps for students in grades 3-5 (5 sessions) and 6-8 (3 sessions) in July and August. These camps were in addition to SV’s regular summer programming on campus, and represented a bold initiative to set up a pilot program off campus. 144 of the 185 available spaces (78%) were filled (with girls being 24% of the total). SV’s program director Melisa Yestrau observes, “We had incredible feedback from parents and campers about the venue and programming.”

RASC members setting up their personal telescopes for public view on the last public observing session for 2014 (6 September). (Photo: J. Hesser)

Similarly, NRC entered a pilot agreement with the Victoria Centre of the Royal Astronomical Society of Canada to take responsibility for public viewing on seven Saturday nights July through early September. RASC exercised full responsibility for programming and interacting with the public, while NRC provided Commissionaires for overall site security and access control, an experienced operator for the Plaskett Telescope, and trained four RASC members to operate the Plaskett safely. RASC volunteers operated their personal telescopes for night viewing, as well as provided all the tours in the Plaskett dome. 2202 members of the public participated, with reactions being very enthusiastic. Don Moffatt’s and Lana Popham’s continued strong support was evident through their participation throughout the summer. In addition, Don arranged for flautist Martina Peladeau and guitarist Ian Bezpalko each to provide lovely music in the Plaskett dome at the beginning of more than half the evenings.

We’ll be gathering the lessons learned and looking at what they portend for 2015, but enthusiasm among the two community groups to continue upon their 2014 successes already seems apparent.

15m Dish Verification Antenna (DVA1)

NRC’s SKA Dish Verification Antenna 1

The NRC has begun testing its 15m Dish Verification Antenna (DVA1) a novel prototype for the Square Kilometre Array (SKA). The antenna is optimised for mass production, low cost and high performance – key requirements for SKA antennas. The antenna is an offset Gregorian design developed in collaboration with the US Technology Development Program (US-TDP). A key innovation is the rim supported primary and secondary reflectors that are a carbon fibre composite monocoques design developed at the NRC’s Dominion Radio Astrophysical Observatory, near Penticton. The reflectors are made in a single piece on a precision mold using the vacuum infusion process yielding a precise reflector that can be mass produced with low overall cost.

The primary and secondary have been measured and are within 0.89 mm and 0.2 mm of ideal. Using better molds the NRC team has demonstrated that these errors can be halved yielding reflectors that operate to 20+ GHz and are very stable over temperature, wind and gravity loads compared to conventional approaches.

First Light on the Sun @ 11.75 to 13.25 GHz

Testing of the DVA1 is well underway. First light at Ku band on the Sun was achieved at the beginning of August, with holography, pointing and antenna temperature measurements to be completed this fall.

Maunakea Spectroscopic Explorer (MSE)

The Maunakea Spectroscopic Explorer (MSE, formerly ngCFHT) continues to make important progress as it begins a Construction Proposal Phase that will last approximately 3.5 years, and which is led by the newly formed Project Office. Important progress in the last few months includes:

• the formation of a Science Team, currently with over 60 members including 10 members from Canada, as well as members from Australia, China, France, Hawaii, India, Japan, mainland USA and elsewhere. August saw the start of science team activities, with White Papers solicited to provide new input to the science development.
• the formation of a Science Executive with Contact Scientists from Australia (Andrew Hopkins), Canada (Michael Balogh), France (Nicolas Martin), India (Gajendra Pandey), with other partner countries soon to have representation. This group provides leadership of the science team in collaboration with the Project Scientist (Alan McConnachie).
• the ranking of MSE in the top priority bracket for development in the first draft of France’s new 5-year Prospective (roughly equivalent to their LRP). MSE and CFHT remain engaged in the ongoing development of the Prospective.
• establishment of much of the basic infrastructure required to operate the Project Office, with headquarters in Waimea.
• exploration of permitting issues and options for MSE consistent with the Maunakea Comprehensive Management Plan.
• visits and important discussions with our colleagues in China, the Republic of Korea, Taiwan and Japan regarding partnership engagement in the future development of CFHT and MSE, and a planned visit to India this Fall.

Please do not hesitate to contact the following for any questions relating to MSE:

• MSE Project Scientist (Alan McConnachie; mcconnachie@mse.cfht.hawaii.edu)
• Project Manager (Rick Murowinski; murowinski@mse.cfht.hawaii.edu)
• CFHT Executive Director (Doug Simons; simons@cfht.hawaii.edu)

Visit the MSE website at mse.cfht.hawaii.edu for more information and recent news.

NFIRAOS

For the past few months, the NFIRAOS team has been working diligently to engage Canadian industry to progress the NFIRAOS’ opto-mechanical subsystems to final design level in time for the Final Design Review planned for late 2016. Eventually, Canadian industry will construct (fabricate, assemble and test) and deliver these subsystems to NRC-Herzberg for overall system integration before delivery to the TMT Observatory.

The planned out-sourced NFIRAOS subsystems, from 2014 to 2015, are:

1. Off-Axis Paraboloids (OAP) mirrors and mounts – a total of six units are required.
2. Beamsplitter (BS) changer with science and engineering beamsplitters, visible light BS and mounts – the science BS separates the infrared science light from the visible wavefront sensor (WFS) light and sends the science light to the client instruments. The visible light BS further separates the WFS light into laser guide star (LGS) path and visible natural WFS (VNW) path for natural guide star (NGS) wavefront sensing. The BS changer switches to the engineering BS to facilitate NFIRAOS assembly and integration.
3. Instrument selection fold mirror (ISM), mount and rotating mechanism – the ISM reflects the infrared science light and feeds the client instruments, and the rotation mechanism directs light to the top, side and bottom instrument ports of NFIRAOS.
4. Source simulators assembly – this contains the elements to provide artificial light sources for NGS, LGS and astrometry calibrations. The opto-mechanical components include dithering pinhole mask, deployable fold mirror for NGS sources, carriage for LGS sources, overall structural support and the associated motion control hardware.
5. LGS path bench assembly – this contains optics, mounts and opto-mechanical mechanisms for the trombone, pickup mirrors, field stops, collimators, six optical barrels which interface with the TMT supplied detector units, overall LGS path structural support and the associated motion control hardware.
6. VNW bench assembly – this contains optics, mounts and opto-mechanical mechanisms for the packaging fold mirrors, star selection unit, atmospheric dispersion compensator, field stop, fast steering mirrors, switchyard, and NGS optical barrel which interface with the TMT supplied detector unit, Truth wavefront sensor (TWFS) unit, overall VNW path structural support and the associated motion control hardware.
7. High resolution wavefront sensor (HRWFS) and acquisition camera (ACQ) assembly – this contains optics, mounts and opto-mechanical mechanisms to enable high resolution wavefront sensing, low and high resolution imaging with a common detector over the full NFIRAOS field of view, and the associated motion control hardware. It also contains the overall structural support to mount the HRWFS and ACQ assembly on the side port.
8. Turbulence generator assembly – this contains optics, mounts and opto-mechanical mechanisms to deploy the turbulence phase screen and transverse between two positions, overall structural support and the associated motion control hardware.

The opto-mechanical subsystems are illustrated in Figure 1. The total value of eight design contracts is $1.7M, ranging from $90K to $300K depending on complexity. The total value of eight construction contracts is $8.5M, ranging from $300K to $3.0M depending on complexity.

NFIRAOS opto-mechanical subsystems

Each contract is divided in at least in two phases, design and construction, where the latter phase will be a binding fixed-price offer for construction after successful completion of the subsystem’s final design. A public information meeting was held on Aug 28 to discuss our out-sourcing plan with potential vendors and solicit their feedback. Six companies attended the meeting.

Meerkat Reflectors

NRC Herzberg has a contract with General Dynamics Satcom (GD Satcom) to fabricate two 4 m diameter sub-reflectors and to transfer our technology to them for the fabrication of the remaining sixty two reflectors. The first two reflectors were built in Penticton and delivered before the end of our fiscal year 2013-2014. The reflectors were fabricated in a single piece from vacuum infused carbon fibre. The reflectors both had a surface RMS of 0.1 mm; easily meeting the contract specification of 0.245 mm RMS. The reflectors represent a very light (<100 kg), very simple alternative to the traditional metal multi-piece design (they come off the mold with the correct shape and require no further adjust), and the weight savings allow a further reduction in structural support weight as well as easier handling. The next phase will involve travelling to Johannesburg South Africa to train a local team to fabricate the remaining units.

From Sylvie Beaulieu, Herschel-HIFI Instrument Support Scientist

Herschel feature story

The current (September 2014) Herschel Feature Story on the Herschel website is Young Sun’s Violent History Solves Meteorite Mystery.

Continued support for using Herschel Science Archive data

On the 29th of October 2013, the last proprietary science observation was released into public domain through the Herschel Science Archive. This represents an excellent opportunity for additional astronomical discoveries for the larger Canadian astronomical community. The University of Waterloo Herschel-HIFI Group remains dedicated to help you achieve your scientific goals.

Herschel Interactive Processing Environment (HIPE)

HIPE 12.1 is the current released version. Please visit What’s New in HIPE for the latest changes in this release. The task hebCorrection can help mitigate the electric standing waves in HEB (bands 6 and 7). Detailed instructions on how to use the task are in the HIFI Data Reduction Guide. Additional information can be found in the HIFI Instrument and Calibration webpage, under Outstanding Calibration Issues.

Warning: a major bug in gain fitting was discovered in the doDeconvolution task. When running the task, this feature should not be used. A revamp of the task (and its documentation) is underway for HIPE 13. Stay tune…

At last! New HIFI beam release

The HIFI team has released a revised version of their beam, involving in particular updates to the coupling efficiencies and Half-Power-Beam-Width, and the delivery of detailed 2D beam models in each HIFI band. A new section of the HIFI calibration page has been created to this effect and Users are invited to carefully read the release notes prepared with these updates. In particular, we want to emphasise that the newly derived aperture and main beam efficiencies have dropped by up to 10% and 20% respectively, leading to equivalent increase of the converted fluxes or main beam temperatures. If you need any additional information in that respect please contact the Helpdesk.

Conferences, workshops and webinars related to Herschel

• “Universe Explored by Herschel” conference proceedings now available online.
• NHSC Herschel Workshop: “The Hitchhiker’s Guide to Extracting SEDs and Spectra from the Herschel Science Archive”, 6-10 October 2014, Pasadena, California.
• Star Formation Across Space and Time, ESA/ESTEC Noordwijk, 10-14 November 2014

Par/by Marie-Michèle Limoges
Thèse défendue le 18 août 2014; Thesis defended on August 18th 2014
Département de physique, université de Montréal
Directeur de thèse/thesis advisor: Pierre Bergeron (U de Montréal)
Co-directeur/co-advisor: Sébastien Lépine (Georgia State U)

Résumé (English version follows)

Les étoiles naines blanches représentent la fin de l’évolution de 97% des étoiles de notre galaxie, dont notre Soleil. L’étude des propriétés globales de ces étoiles (distribution en température, distribution de masse, fonction de luminosité, etc.) requiert l’élaboration d’ensembles statistiquement complets et bien définis. Bien que plusieurs relevés d’étoiles naines blanches existent dans la littérature, la plupart de ceux-ci souffrent de biais statistiques importants pour ce genre d’analyse. L’échantillon le plus représentatif de la population d’étoiles naines blanches demeure à ce jour celui défini dans un volume complet, restreint à l’environnement immédiat du Soleil, soit à une distance de 20 pc (∼65 années-lumière) de celui-ci. Malheureusement, comme les naines blanches sont des étoiles intrinsèquement peu lumineuses, cet échantillon ne contient que ∼ 130 objets, compromettant ainsi toute étude statistique significative. Le but de notre étude est de recenser la population d’étoiles naines blanches dans le voisinage solaire à une distance de 40 pc, soit un volume huit fois plus grand.

Nous avons ainsi entrepris de répertorier toutes les étoiles naines blanches à moins de 40 pc du Soleil à partir de SUPERBLINK, un vaste catalogue contenant le mouvement propre et les données photométriques de plus de 2 millions d’étoiles. Notre approche est basée sur la méthode des mouvements propres réduits qui permet d’isoler les étoiles naines blanches des autres populations stellaires. Les distances de toutes les candidates naines blanches sont estimées à l’aide de relations couleur-magnitude théoriques afin d’identifier les objets se situant à moins de 40 pc du Soleil, dans l’hémisphère nord. La confirmation spectroscopique du statut de naine blanche de nos ∼ 1100 candidates a ensuite requis 15 missions d’observations astronomiques sur trois grands télescopes à Kitt Peak en Arizona, ainsi qu’une soixantaine d’heures allouées sur les télescopes de 8 m des observatoires Gemini Nord et Sud. Nous avons ainsi découvert 322 nouvelles étoiles naines blanches de plusieurs types spectraux différents, dont 173 sont à moins de 40 pc, soit une augmentation de 40% du nombre de naines blanches connues à l’intérieur de ce volume. Parmi ces nouvelles naines blanches, 4 se trouvent probablement à moins de 20 pc du Soleil. De plus, nous démontrons que notre technique est très efficace pour identifier les étoiles naines blanches dans la région peuplée du plan de la Galaxie.

Nous présentons ensuite une analyse spectroscopique et photométrique détaillée de notre échantillon à l’aide de modèles d’atmosphère afin de déterminer les propriétés physiques de ces étoiles, notamment la température, la gravité de surface et la composition chimique. Notre analyse statistique de ces propriétés, basée sur un échantillon presque trois fois plus grand que celui à 20 pc, révèle que nous avons identifié avec succès les étoiles les plus massives, et donc les moins lumineuses, de cette population qui sont souvent absentes de la plupart des relevés publiés. Nous avons également identifié plusieurs naines blanches très froides, et donc potentiellement très vieilles, qui nous permettent de mieux définir le côté froid de la fonction de luminosité, et éventuellement l’âge du disque de la Galaxie. Finalement, nous avons aussi découvert plusieurs objets d’intérêt astrophysique, dont deux nouvelles étoiles naines blanches variables de type ZZ Ceti, plusieurs naines blanches magnétiques, ainsi que de nombreux systèmes binaires non résolus.

Abstract

White dwarf stars represent the endpoint of stellar evolution for 97% of stars in the Galaxy. Our own Sun, in particular, will lose its external gas layers in about 5 billion years, and end up as an Earth-sized white dwarf. The study of their global properties (temperature distribution, mass distribution, luminosity function, etc.) requires statistically complete samples, free from any selection bias, and thus the best strategy to adopt when surveying these low-luminosity objects is to restrict the search to a given volume such as the immediate vicinity of the Sun. However, the current census of white dwarfs in the solar neighborhood suffers from significant statistical biases, since the most representative sample of the local white dwarf population, i.e. the stars within a sphere with a radius of 20 pc from the Sun (∼ 65 light-years), contains only ∼ 130 objects, and is thus dominated by large uncertainties due to small-number statistics. In order to perform a statistical analysis of the local white dwarf population which is more statistically significant, we present a study aimed at obtaining a complete sample of white dwarfs in the solar neighborhood within 40 pc of the Sun, thus increasing the sampled volume by a factor of 8.

To identify every white dwarf within 40 pc of the Sun, we rely on SUPERBLINK, a large catalog containing proper motions and photometric information for over 2 million stars. Our approach is based on reduced proper motion diagrams, which are efficient at separating white dwarfs from other stellar populations. The distances for all white dwarf candidates in the northern hemisphere are determined from theoretical color-magnitude relations, in order to identify the stars that lie within 40 pc of the Sun. The spectral confirmation of the resulting ∼ 1100 candidates required 15 observing runs with 3 large telescopes at Kitt Peak, Arizona, as well as ∼ 60 hours of allocated time on the 8-m telescopes of Gemini North and South Observatories. From these spectroscopic observations, we identified 322 new white dwarf stars, among which 173 lie within 40 pc the Sun, thus increasing the current census of white dwarfs in this volume of space by 40%. Among the new white dwarf identifications, 4 could even belong to the 20 pc sample. We also show that our method is efficient at recovering white dwarfs in the densely populated area of the Galactic plane.

We then present a spectroscopic and photometric analysis of our sample with state-of-the- art model atmospheres in order to determine their physical properties, in particular the effective temperature, surface gravity, and chemical composition of each star. Our statistical analysis of these properties — based on a sample almost three times larger than the 20 pc sample—reveals that we are successfully uncovering the most massive and thus less luminous stars of this population, which are often missing in most surveys reported in the literature. We also identify a significant number of very cool and thus potentially old white dwarfs, which are useful to sample the cool end of the luminosity function used to constrain the age of the Galactic disk. Finally, we report the discovery of several objects of astrophysical interest, including two new ZZ Ceti variable stars, several magnetic white dwarfs, and a few unresolved double degenerate binaries.