BRITE-Constellation Mission Update

By / par Gregg Wade (Canadian PI for BRITE)
(Cassiopeia – Autumn / l’automne 2018)

BRITEpatch

BRITE-Constellation is an international space astronomy mission consisting of a fleet of 20x20x20 cm nanosatellites dedicated to precision optical photometry of bright stars in two photometric colours. The mission continues in full science operations, with 25 data releases to BRITE target PIs having already taken place, and many datasets available in the public domain from the BRITE public archive.

The BRITE mission is a collaboration between Canadian, Austrian and Polish astronomers and space scientists. The Canadian partners represent University of Toronto, Université de Montréal, Bishop’s University, and Royal Military College of Canada. The mission was built, and the Canadian satellites operated by, the University of Toronto Institute for Aerospace Studies Space Flight Lab (UTIAS-SFL). The Canadian Space Agency funded the construction of the Canadian satellites, and continues to support their day-to-day operations.

Operations

There are five operating BRITE satellites in the Constellation, collecting data on various sky fields in a coordinated programme to obtain well-sampled, longterm continuous (~6 months) light curves in both red and blue bandpasses.

As this issue of Cassiopeia went to press, here was the status of the sky assignments for the BRITE cubesats:

  • BRITE Toronto (Canada): Toronto observes with a red filter. It is currently observing the Cygnus III and Cassiopeia III fields, switching between the two fields each orbit. As implied by the numeral ‘III’, the current campaigns on these fields represents revisits of previously-observed fields.
  • BRITE Lem (Poland): Lem observes with a blue filter. It is also observing the Cygnus III field.
  • BRITE Heweliusz (Poland): Heweliusz observes with a red filter. This satellite is observing the Cygnus III field, but will soon transition to another field (details TBD).
  • BRITE Austria (Austria): BRITE Austria observes with a blue filter. It is observing the Sagittarius IV and the Cassiopeia III fields.
  • UniBRITE (Austria): UniBRITE observes with a red filter. This satellite is currently observing the Cygnus III and Cassiopeia III fields.

The BRITE Constellation observing programme from early 2017 through to mid-2019 has been planned by the BRITE Executive Science Team (BEST), and details are available on the BRITE photometry Wiki page.

Recent Science Results

Figure 1: The two-month long BRITE light curve of V973 Sco (red filled circles) as recorded in 2015 in the red passband by BRITE-Heweliusz, along with the contemporaneous observations of phi 2 Lup (black diamonds, offset by 50 mmag for better visibility) showing no significant variability. From Ramiaramanantsoa et al. (2018).

“A BRITE view on the massive O-type supergiant V973 Scorpii: hints towards internal gravity waves or sub-surface convection zones” (Ramiaramanantsoa et al. 2018, MNRAS 480, 972). The authors report detection of stochastically-triggered photospheric light variations reaching ~40 mmag peak-to-valley amplitudes in the O8Iaf supergiant V973 Scorpii as the outcome of two months of high-precision time-resolved photometric observations with the BRITE nanosatellites. The amplitude spectrum of the time series photometry exhibits a pronounced broad bump in the low-frequency regime (<0.9 c/d) where several prominent frequencies are detected. A time-frequency analysis of the observations reveals typical mode lifetimes of the order of 5−10 days. The overall features of the observed brightness amplitude spectrum of V973 Sco match well with those extrapolated from two-dimensional hydrodynamical simulations of convectively-driven internal gravity waves randomly excited from deep in the convective cores of massive stars. An alternative or additional possible source of excitation from a subsurface convection zone needs to be explored in future theoretical investigations.

“Short-term variability and mass loss in Be stars IV. Two groups of closely spaced, approximately equidistant frequencies in three decades of space photometry of ν Puppis (B7-8 IIIe)” (Baade et al., submitted to A&A). In early-type Be stars, groups of nonradial pulsation (NRP) modes with numerically related frequencies may be instrumental for the release of excess angular momentum through mass-ejection events. Difference and sum/harmonic frequencies often form additional groups. The goal of this study is to find out whether a similar frequency pattern occurs in the cooler third-magnitude B7-8 IIIe shell star ν Pup. Time-series analyses are performed of space photometry with BRITE-Constellation (2015, 2016/17, and 2017/18), SMEI (2003–2011), and Hipparcos (1989-1993). Two IUE SWP and 27 optical echelle spectra spanning 20 years were retrieved from various archives. The optical spectra exhibit no anomalies or well-defined variabilities. A magnetic field was not detected. All three photometry satellites recorded variability near 0.656 c/d which is resolved into three features separated by ~0.0021 c/d. First harmonics form a second frequency group, also spaced by ~0.0021 c/d. The frequency spacing is very nearly but not exactly equidistant. Variability near 0.0021 c/d was not detected. The long-term frequency stability could be used to derive meaningful constraints on the properties of a putative companion star. The IUE spectra do not reveal the presence of a hot subluminous secondary. ν Pup is another Be star exhibiting an NRP variability pattern with long-term constancy and underlining the importance of combination frequencies and frequency groups. The star is a good target for efforts to identify an effectively single Be star.

Conferences, Resources and Social Media

Conferences

The BRITE Executive Science Team recently met in Wroclaw, Poland for two days of scientific and administrative discussions. Thirteen scientific presentations were delivered on topics ranging from BRITE CCD cosmetics to time-domain astronomy with BRITEs.

The proceedings of the third BRITE Science Conference – held at Lac Taureau, Canada in August 2017 – are available in printed form and online.

The BRITE team is spearheading the organization of a conference entitled “Stars and their Variability, Observed from Space”, to occur in Vienna, Austria from August 19 – 23, 2019. Preregistration is available on the conference website.

Resources

The BRITE Public Data Archive, based in Warsaw, Poland, at the Nikolaus Copernicus Astronomical Centre, can be accessed at brite.camk.edu.pl/pub/index.html.

The mission Wiki (including information on past, current and future fields) can be accessed at brite.craq-astro.ca/.

BRITE Constellation is on Facebook, at @briteconstellation.

The BRITE International Advisory Science Team

The BRITE International Advisory Science Team (BIAST), which consists of BRITE scientific PIs, technical authorities, amateur astronomers, and mission fans, advises the mission executive on scientific and outreach aspects of the mission. If you’re interested to join BIAST, contact Canadian BRITE PI Gregg Wade: wade-g@rmc.ca.

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