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Getting to Know a Familiar Star

The 60th Carnival of Space is now up at Slacker Astronomy, and if you want to see some fine science writing, I’ll point you this week to the host, whose essay on Regulus shows what can be done when a scientist with serious writing skills takes apart an interesting scientific paper. Doug Welch knows what he’s talking about — he’s a professor of physics and astronomy at McMaster University (Hamilton, ONT), deeply involved in dark matter studies, supernovae and variable stars. So it’s no surprise that the interesting story of Regulus and its apparent companion comes alive in Slacker Astronomy‘s pages.

What about Regulus? A team led by Doug Gies (Georgia State) has studied this bright, ecliptic-hugging star for evidence of a hitherto unknown companion. The result:

They found that Regulus was indeed a spectroscopic binary. Once every 40.11 days, the system completes one orbit. Regulus itself has a mass of about 3.4 times that of the Sun. The companion of Regulus is much less massive – only about 0.30 solar masses. Such a small mass object is either a low-mass star or a white dwarf. The latter possibility provides an explanation for Regulus’ rapid rotation! The idea is that the companion was once the more massive member of the pair and when it finished hydrogen burning in its core, it expanded dramatically and started losing mass to Regulus in a manner which “spun it up”. A mass of 0.30 solar masses is very low for a white dwarf – such objects are found only in systems where it is clear that much mass has been transferred.

Intriguingly, spectra taken by the International Ultraviolet Explorer satellite showed results consistent with a white dwarf but not a cool, low-mass star. The case for a white dwarf seems confirmed, a reminder that objects we thought we knew well often yield up their secrets only slowly, and with the necessary improvements in our instrumentation. And if you have a fascination, as I do, with how these studies work, be sure to read Welch’s comments on the instruments involved, including the Kitt Peak National Observatory Coude Feed Telescope, about which this:

A Coude room is very high-resolution spectrograph capable of tearing the light from a telescope into very fine shreds of color. It was designed to be fed by the 2.1m telescope at Kitt Peak. However, observatories tend to do deep imaging around the time of New Moon (i.e. when the sky is dark) and the 2.1m served a variety of such needs. It was realized that the a smaller telescope could “feed” the spectrograph during these periods and that brighter stars could be observed with that smaller telescope plus Coude spectrograph while the big telescope was busy imaging!

This is solid science writing. Taking state of the art instrumentation and breaking it down into not just comprehensible but readable terms is hard work, and Welch does the same with GSU’s Multi-Telescope Telescope. Slacker Astronomy quickly goes into my essential RSS list. I also want to point you to a site already firmly ensconced in that list, Brian Wang’s NextBigFuture, which (among many other things) this week discussed the Space Elevator power beaming competition. Finding the cheapest route to low-Earth orbit is an essential for making a true space-based infrastructure a reality, and few concepts are as visionary as the Space Elevator. Add commercial competition to the mix and watch the ideas fly.

Comments on this entry are closed.

  • ljk July 30, 2008, 0:13

    The impact of the oblateness of Regulus on the motion of its companion

    Authors: Lorenzo Iorio

    (Submitted on 26 Jul 2008)

    Abstract: The fast spinning B-star Regulus has recently been found to be orbited by a fainter companion in a close circular path with orbital period P_b = 40.11(2) d. Being its equatorial radius R_e 32% larger than the polar one R_p, Regulus possesses a remarkable quadrupole mass moment Q.

    We investigate the effects of Q on the orbital period P_b of its companion in order to see if they are measurable, given the present-day level of accuracy in measuring P_b. Conversely, we will look for deviations from the third Kepler law, attributed to the quadrupole mass moment Q of Regulus, to constrain the ratio \gamma=m/M of the system’s masses.

    Comments: LaTex, 19 pages, 7 figures, 1 table

    Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph); Space Physics (physics.space-ph)

    Cite as: arXiv:0807.4221v1 [gr-qc]

    Submission history

    From: Lorenzo Iorio [view email]

    [v1] Sat, 26 Jul 2008 07:22:27 GMT (38kb)


  • ljk August 4, 2008, 23:21

    Next on NOVA scienceNOW

    With Neil deGrasse Tyson

    Wednesday, August 6 at 9 p.m.

    (Check your local listings as dates and times may vary.)

    This broadcast looks at attempts to build a space elevator, how we
    age, a new technique for finding Maya ruins, and a profile of
    biologist Bonnie Bassler.

    Space Elevator


    Can we build a 22,000-mile-high cable to transport cargo and
    people into space?

  • ljk December 24, 2008, 8:35

    December 23, 2008

    New Space Elevator Consortium

    Written by Nancy Atkinson

    A coalition of leaders working on the concept of a space elevator has joined forces to form the International Space Elevator Consortium (ISEC). The new independent group is designed to promote standards and foster research relating to the construction of an Elevator to Space at the global level. Founding members of ISEC include the Spaceward Foundation, the Space Elevator Reference, the Space Elevator Blog, EuroSpaceward and the Japan Space Elevator Association. Heading the new organization is Ted Semon of the Space Elevator Blog, who will serve as president. Michael Laine, president of the space elevator company Liftport is excited about the consortium.

    “I think it’s a great thing,” he said. “This has been in the works for months, and the need to bring the different organizations under one roof has been long overdue. All five of the major organizations have been acting independently, which made sense in the beginning, but now we need coordination and cooperation.”

    “The Space Elevator is a project whose time has come,” said Semon. “With the challenges facing today’s global economy, it is clear that new industries and new ideas are needed to help our planet in the 21st Century. The Space Elevator can be a key positive contributor, from providing inexpensive nanotechnology material science breakthroughs that will make your car stronger and lighter, to the creation of new industries that offer opportunities for investment and job creation. The International Space Elevator Consortium devoted to its development can make this happen.”

    Full article here:


  • ljk April 3, 2009, 13:33

    The Past and Future History of Regulus

    Authors: S. Rappaport (MIT), Ph. Podsiadlowski (Oxford), I. Horev (Technion)

    (Submitted on 2 Apr 2009)

    Abstract: We show how the recent discovery of a likely close white dwarf companion to the well known star Regulus, one of the brightest stars in the sky, leads to considerable insight into the prior evolutionary history of this star, including the cause of its current rapid rotation.

    We infer a relatively narrow range for the initial masses of the progenitor system: M_{10} = 2.3 +/- 0.2 M_sun and M_{20} = 1.7 +/- 0.2 M_sun, where M_{10} and M_{20} are the initial masses of the progenitors of the white dwarf and Regulus, respectively.

    In this scenario, the age of the Regulus system would exceed 1 Gyr. We also show that Regulus, with a current orbital period of 40 days, has an interesting future ahead of it. This includes (i) a common envelope phase, and, quite possibly, (ii) an sdB phase, followed by (iii) an AM CVn phase with orbital periods < 1 hr.

    Binary evolution calculations are presented in support of this scenario. We also discuss alternative possibilities, emphasizing the present uncertainties in binary evolution theory. Thus, this one particular star system illustrates many different aspects of binary stellar evolution.

    Comments: PDFLaTeX, 9 pages with 8 figures

    Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

    Cite as: arXiv:0904.0395v1 [astro-ph.SR]

    Submission history

    From: Saul Rappaport [view email]

    [v1] Thu, 2 Apr 2009 14:10:15 GMT (1601kb,D)