MOST… Cutting To The Heart Of A Wolf-Rayet Star


In 1867, astronomers using the 40 cm Foucault telescope at the Paris Observatory, discovered three stars in the constellation Cygnus (now designated HD191765, HD192103 and HD192641), that displayed broad emission bands on an otherwise continuous spectrum. The astronomers’ names were Charles Wolf and Georges Rayet, and thus this category of stars became named Wolf–Rayet (WR) stars. Now using the Canadian MOST microsatellite, a team of researchers from the Universite de Montreal and the Centre de Recherche en Astrophysique du Quebec have made a stunning observation. They probed into the depth of the atmospheric eclipses in the Wolf-Rayet star, CV Serpentis, and observed a never before seen change of mass-loss rate.

Thanks to the service of MOST – Canada’s first space telescope and its high precision photometry – the team has observed significant changes in the depth of the atmospheric eclipses in the 30-day binary WR+O system. The equipment is aboard a suitcase-sized microsatellite (65 x 65 x 30 cm) which was launched in 2003 from a former ICBM in northern Russia. It is on a low-Earth polar orbit and has long outlived its original estimated life expectancy, offering Canadian astronomers almost eight years (and still counting) of ultra-high quality space-based data. Now this data gives us a huge insight into the heart of Wolf-Rayet stars.

Intrinsically luminous, WR stars can be massive or mid-sized, but the most interesting stage is arguably the last 10% in the lifetime of the star, when hydrogen fuel is used up and the star survives by much hotter He-burning. Towards the end of this phase, the copious supply of carbon atoms head for the stellar surface and are ejected in the form of stellar winds. WR stars in this stage are known as WC stars… and their production of carbon dust is one of the greatest mysteries of the Cosmos. These amorphous dust grains range in size from a few to millions of atoms and astronomers hypothesize their formation may requires high pressure and less than high temperatures.

“One key case is undoubtedly the sporadic dust-producing WC star in CV Ser. MOST was recently used to monitor CV Ser twice (2009 and 2010), revealing remarkable changes in the depths of the atmospheric eclipse that occurs every time the hot companion’s light is absorbed as it passes through the inner dense WC wind.” says the researchers. “The remarkable, unprecedented 70% change in the WC mass-loss rate might be connected to dust formation.”

And all thanks to the MOST tiny little satellite imaginable…

Original Story Source: AstroNews and excerpt from Wikipedia.

13 Replies to “MOST… Cutting To The Heart Of A Wolf-Rayet Star”

  1. Correct me if I’m wrong, are these stars spraying diamond dust into the cosmos? What an interesting sight that would be.

      1. Graphene comes to mind. Some of the sheets of carbon will also form into buckyballs of both flavors. It all is good though. There might be forms of carbon arrangements we could use commercially if they were closer. Some of these stellar produced forms might be within our system as a part of the initial impurities contained within the cloud of origination.


    1. Well, you _do_ get “diamond-like” material from carbon and hydrogen in similar environments on Earth (industrial low-pressure chambers, with thermal or plasma or irradiation activation).

      However, the bearer would be dust, it would be minute amounts of the whole, and it is not well-ordered* so no crystals.

      * It has some of the bond angles and so hardness of diamond rather than graphite. It also usually contains remains of the hydrogen that helped form it.

  2. While I think it’s OK fair use that the first two sentences were copied verbatim out of a Wikipedia article, I think one should source any quotation used, even Wikipedia.

    1. I agree with you on proper attribution.

      The original news release Tammy is using for her source material might be using data derived from that wiki article, there are many of them, search for the phrase “In 1867, astronomers using the 40 cm Foucault telescope at the Paris Observatory” to see some of the provenance of the quoted material both recently and several years old. The history of the page on wiki shows IVAN3MAN as one of the contributors, can we ask him where the first two paragraphs originated for a more profound provenance.


      1. i’ve added an attribute so no one feels that something was left out. thanks for correcting me!

      2. Note that Wikipedia uses a CC-BY-SA license. The “CC” stands for “Creative Commons”. The “BY” stands for “By Attribution”. The “SA” stands for “Share-Alike”.

        What that means is that you can copy and modify Wikipedia’s content in any way that you desire, but that you *have* to give attribution, and your work also has to use a CC-BY-SA licensing scheme. If not, it is considered a copyright violation.

        This site does not use a Creative Commons license, and so *cannot* copy things from Wikipedia verbatim, although Wikipedia’s content can of course be synthesized here.

  3. First of all – great to see MOST still kicking along! What a great little scope it has been.

    Second – how the hell is ‘Rayet’ pronounced? I’ve heard it said so many different ways (even by astronomers) that I’ve decided to try to build a consensus for my own benefit. Maybe when I’m in France later this year I’ll have to ask someone to say the name for me!

    1. Here is my read on this for your records.

      Normally pronouncing it as RaY-Et is correct, however, the accent is on the first syllabic break, in other words from the last letter of the first word and carried over (slurred) to the second syllables first letter, much like I have shown. This enunciation was more common in the last decade of that century.

      The roots of the name are drawn from French, Spanish, Dutch and German origins depending on the ancestry of the holder and, in some cases, the choice made by the holder to indicate a different ancestry than what is actual for them.

      The French and Spanish languages have it as Rey-et or Ray-et with no other accent than the R in Rey and the -et syllable can be swallowed whole or in part if you desire.

      Going with Ray-ETTE will be incorrect unless you posit this surname is directly from a prior and longer form French surname or maternal surname plus title with appellation such as Rayette (for a chosen middle name not derived from shared lines), or entered that arena via some alternate spelling of Dutch, Spanish, or German ancestry. As far as I know there is no Italian form nor is there any Russian, Chechen, or other Slavic root for this name.

      The way the ‘owner’ says it rules though. Shame we can’t ask.


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