Chapter 22:

Doubles, Variables and Clusters

What's New Updates by Chapter Astro Pages Ordering

Interferometry on Stars

The CHARA (Center for High Angular Resolution Astronomy) Array is currently under construction on Mt. Wilson in the form of a five-telescope array with maximum baseline of 350 meters to yield limiting resolutions of 0.2 milliarcsecond in the visible and 1.0 milliarcsecond at K-band IR. The individual telescopes have apertures of 1.0 m. The instrument will be used for Michelson interferometry and closure-phase imaging, and is expected to have a limiting sensitivity that will make the brightest AGN's just accessible. Its primary scientific program will be the fundamental astrophysics of stars (masses, radii, effective temperatures, surface features, luminosities, distances, etc.) The November SKY AND TELESCOPE will have a blurb about the project, along with a computer generated picture of what it will look like on Mt. Wilson, accompanying a longer article on my binary star speckle work. from Hal McAlister, Georgia State University

Evidence found for an early generation of stars in the Universe

Astronomers talk not only of Population I and II stars but also of Population III, which appeared earlier on in the Universe's evolution and which have since disappeared. New observations with the Keck Telescope reported by Len Cowie and Antoinette Songaila of the University of Hawaii show that one atom in a million in the intergalactic medium is highly ionized carbon. This is a higher concentration than had been expected in these clouds, which had been thought to have been pristine hydrogen and helium left over from the Big Bang.

Since the carbon could have been created only inside stars, the evidence indicates to Cowie and Songaila that there was "an early generation of stars that formed prior to the period of galaxy formation. Our observations could be the first evidence for this population."

The observations were made between redshifts 2.5 and 3.0, which puts the gas about 10 billion light-years away. They studied the light from background quasars, and reported that only the new large telescope and its efficient spectrograph made these observations possible.

For More Information

Reference: Astronomical Journal for April 1995

Corrections

  • p. 380, Fig. 22-23, line 5: "detect"
  • p. 383, Fig. 22-28 caption: the top and bottom views of M14 are reversed
  • p 369 says that the separation limit visually is as low as 0".08. The speckle observations at large telescopes reach about 0".03.
  • Fig 22-6 caption, p. 372: The difference lies in the orbit size, not the inclination. The ratio orbit/star size is around 1000 for visual pairs, 10 or less for eclipsing binaries.
  • p 373: The Moon passes over 1% of sky in a year, or 2.5% when parallax is included (i.e. when observed from widely different latitudes). The 10% are reached only over the full 19-yr nodal cycle.
  • p.370 The presence of companions of different spectral types has now been studied in detail. Long before the spectral work, the number 85% for the percentage of double stars was already established in studies by Dr. W. Heintz of Swarthmore College.

I thank Prof. Wulff Heintz of Swarthmore College for these corrections.

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