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Proxima Dwarf ?

jjswaim schrieb/wrote/a écrit:

> ... the discovery of Epsilon Centauri a couple of months |ago,  ...

Hello Julia and List,

News Notes, Sky & Telescope, May 1998, p. 21: A Proxima Dwarf ?

Astronomers using the Hubble Space Telescope may have detected a faint
companion orbiting Proxima Centauri. A team led by Alfred B. Schultz
(Space Telescope Science Institute) obtained two images of the nearest
star to the Sun using the Faint Object Spectrograph (FOS). Taken 103
days apart, they reveal a tiny speck, with an estimated red magnitude of
16, that appears to move with Proxima across the sky. The two bodies'
apparent separation increased from 0.23" in the first image to 0.34" in
the second suggesting an eccentric orbit. Schultz’s group claims it may
have spotted a brown dwarf or giant planet.
One possible alternative - that the FOS captured a chance alignment with
a more distant star - seems to be ruled out by the companion's motion.
In addition, a search of HST data archives down to 23rd red magnitude
didn’t turn up any background object in the same position. In the
January 1998 Astronomical Journal, Schultz's team estimates that the
feature's inherent brightness is about six times that of Gliese 229B, a
known brown dwarf. That means it would be glowing with its own light,
not just reflecting Proxima's.
But even Schultz remains cautious about the object's existence, since
there is no other evidence, either from HST or ground-based
observations, to support it. At January’s meeting of the American
Astronomical Society, David A. Golimowski (John Hopkins University) and
Daniel Schroeder (Beloit College) underscored these doubts with pictures
taken by HST's Wide Field and Planetary Camera 2. Despite being able to
see to within 0.09 arc-second of Proxima, the two astronomers found no
evidence for a companion.
So what did the FOS see? Perhaps Proxima itself. Golimowski and
Schroeder suggest that diffraction rings in the star's image could have
been modified by the secondary mirror support in the HST's optical path
into a ring of "beads" much like in an amateur's reflector. They
calculated that just such a bead-ring would be in approximately the same
position, and have the same brightness (about 7.5 magnitudes fainter
than Proxima itself), as Schultz's feature. So which interpretation is
right? Until further studies are made, including a planned session with
another HST instrument, the Near Infrared Camera and Multi-Object
Spectrometer, the jury remains out.


Best wishes,

Bernd

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