BRITE Constellation Mission Update

By/par Gregg Wade, Canadian PI for BRITE
(Cassiopeia – Summer/été 2017)

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 17 data releases to BRITE target PIs having already taken place, and many datasets available in the public domain from the BRITE public archive.

The most recent Call for Proposals closed on 01 December 2016, and 15 new proposals for observation were evaluated.

More information about the mission is available on our website: www.brite-constellation.at. General inquiries about BRITE Constellation should be directed to the BEST Chair, Andrzej Pigulski, Univ. Wroclaw, Poland: pigulski@astro.uni.wroc.pl or to Canadian PI Gregg Wade, RMC: wade-g@rmc.ca.

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 continues observing the Vel/Pic field after a record-breaking 215 days-long run. It is also observing the Ara/Sco field.
  • BRITE Lem (Poland): Lem observes with a blue filter. It is also observing the Vel/Pic field, along with the Sagittarius III field.
  • BRITE Heweliusz (Poland): Heweliusz observes with a red filter. This satellite is observing the Carina field.
  • UniBRITE (Austria): UniBRITE observes with a red filter. It is also observing the Sagittarius III field.
  • BRITE Austria (Austria): BRITE Austria observes with a blue filter. It is also observing the Sagittarius III field.

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

Recent science results and technical papers

Studying the photometric and spectroscopic variability of the magnetic hot supergiant zeta Orionis Aa” (Buysschaert et al. 2017, A&A, in press):
To understand the variability of evolved massive stars in more detail, Buysschaert et al. present a study of the O9.2Ib supergiant zeta Ori Aa, the only currently confirmed hot supergiant to host a magnetic field. They perform a detailed frequency analysis to detect and characterize the star’s periodic variability, detecting two significant, independent frequencies, their higher harmonics, and combination frequencies. We confirm the variability with P_rot/4, likely caused by surface inhomogeneities, being the possible photospheric drivers of the discrete absorption components. No stellar pulsations were detected in the data.

Triple system HD 201433 with a SPB star component seen by BRITE-Constellation: Pulsation, differential rotation, and angular momentum transfer” (Kallinger et al. 2017, A&A, in press):
The SPB star HD 201433 is known to be part of a single-lined spectroscopic triple system, with two low-mass companions orbiting with periods of about 3.3 and 154 d. Kallinger et al. identify a sequence of 9 rotationally split dipole modes in the photometric time series and establish that HD 201433 is in principle a solid-body rotator with a very long rotation period. Tidal interaction with the inner companion has, however, significantly accelerated the spin of the surface layers by a factor of approximately one hundred. The angular momentum transfer onto the surface of HD201433 is also reflected by the statistically significant decrease of the orbital period of about 0.9 s during the last 96 years. Ultimately, the authors conclude that tidal interactions between the central SPB star and its inner companion have almost circularised the orbit but not yet aligned all spins of the system and have just begun to synchronise rotation.

Fig. 2: Final light curve of HD 201433 as obtained with the Canadian BRITE-Toronto satellite. The grey and black dots in the top panel represent the full and binned data, respectively. The bottom panels show enlargements of the full data set (red boxes in the top panel). From Kallinger et al. (2017).

Fig. 1: Final light curve of HD 201433 as obtained with the Canadian BRITE-Toronto satellite. The grey and black dots in the top panel represent the full and binned data, respectively. The bottom panels show enlargements of the full data set (red boxes in the top panel). From Kallinger et al. (2017).

BRITE-Constellation: Data processing and photometry” (Popowicz et al. 2017, A&A, in press):
The main aim of this third fundamental technical paper about BRITE-Constellation data is the presentation of procedures used to obtain high-precision photometry from a series of images acquired by the BRITE satellites in two modes of observing, stare and chopping. Popowicz et al. describe two pipelines corresponding to the two modes of observing. The assessment of the performance of both pipelines is presented. It is based on two comparisons, which use data from six runs of the UniBRITE satellite: (i) comparison of photometry obtained by both pipelines on the same data, which were partly affected by charge transfer inefficiency (CTI), (ii) comparison of real scatter with theoretical expectations. It is shown that for CTI-affected observations, the chopping pipeline provides much better photometry than the other pipeline. For other observations, the results are comparable only for data obtained shortly after switching to chopping mode. Starting from about 2.5 years in orbit, the chopping mode of observing provides significantly better photometry for UniBRITE data than the stare mode. This paper shows that high-precision space photometry with low-cost nano-satellites is achievable. The proposed methods, used to obtain photometry from images affected by high impulsive noise, can be applied to data from other space missions or even to data acquired from ground-based observations.

Fig. 1: Distribution of the observations from all five BRITE satellites until the end of 2016. The data obtained in the stare and chopping observing modes are shown with unfilled and filled bars, respectively. From Popowicz et al. (2017).

Fig. 2: Distribution of the observations from all five BRITE satellites until the end of 2016. The data obtained in the stare and chopping observing modes are shown with unfilled and filled bars, respectively. From Popowicz et al. (2017).

Conferences, resources and social media

Conferences

The 3rd BRITE Constellation Science Conference will be hosted in Canada in August 2017. The conference, entitled “New scientific and technical achievements with BRITE”, will take place at the Auberge du Lac Taureau, located 2.5h north of Montréal, from 6-10 August. Late registration may still be possible by contacting brite2017@astro.umontreal.ca.

Resources

The BRITE Public Data Archive, based in Warsaw, Poland, at the Nikolaus Copernicus Astronomical Center, 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 now 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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