Also known as HH
Andromedae, 2MASS J23415498+4410407,
G 171-010, GCTP 5736.00,
GJ 905, LHS 549
Yet one more red dwarf flare star on our
list, Ross 248 physically has little to distinguish itself from others bearing
that label. Its 12% solar mass and 0.2% solar luminosity makes it pretty much
an average star of the M class. Its surface temperature, however, at a
comfortable 2,800º, tends to the lower end of the scale. Those characteristics
plus its 10.3 ly distance guarantees that Ross 248 will be a faint target
indeed.
But despite its diminutive size and dim
appearance, Ross 248 has managed to punch above its weight within astronomical
and indeed human history since it first came to Frank Elmore Ross’s attention
in 1926. Not long after its inclusion in his second catalog of stars with high
proper motion, astronomers noted that Ross 248 exhibited signs of variability
that could not be accounted for simply by its status as a flare star. Patient
observation over time eventually determined that it quite regularly oscillated
between magnitudes 12.23 to 12.34 over a 4.2 year period. In addition, in 1950
Ross 248 became the first star other than the sun to have its sunspot
(starspot) cycle measured (or even known to exist), by means of tracking minute
variations in luminosity. Three simultaneous unrelated cycles of variability!
Just imagine the effort required to identify which cause (or even combination
of causes) was responsible for whatever specific variation in brightness was
being observed at any particular time.
In time, Ross 248 became the object of an
intensive search for planetary or brown dwarf companions. For years it was
observed through the 24-inch refractor at Swarthmore College’s Sproul
Observatory, looking for wobbles in the star’s motion. But none were
discovered. Later, near infrared speckle interferometry was used, with no
positive results found. Finally, no less than the Hubble Space Telescope turned
its attention to this unprepossessing star, only to come up empty. Although it
remains possible that relatively small planetary companions to Ross 248 do
exist, anything as large as our own solar system’s gas giants has been ruled
out.
Due to its motion through the galaxy
relative to the Sun, Ross 248 will eventually have its turn as the closest star
to us, beginning about 30,000 years from now. Closest approach will occur 6,000
years later, when the star will be a mere 3.024 light years (ly) distance from the solar
system. After that time, it will have passed us by and will begin slowly
receding until, 42,000 years from now, Proxima Centauri will once again be our
nearest stellar neighbor.
Finally, on August 25, 1989, Ross 248
became the first star in the galaxy to be the eventual destination for a
human-built spacecraft. On that date, the Voyager II space probe flew past the
planet Neptune on a speed sufficient to escape the Sun’s gravity and on a
trajectory that will eventually bring the craft (40,176 years from now) to
within 1.76 ly of Ross 248. After that “close approach”, Voyager II will not
come anywhere near to another star until the year 296,000, when it should come
within 4.3 ly of Sirius.
But perhaps by then we may well have
launched somewhat faster probes toward the stars (with human passengers on
board?), which might get there first.
Observing Ross 248 with a small telescope (currently, my largest is a 102mm refractor) is a practical impossibility, and it
is the only red dwarf theoretically visible from Maryland that
I have yet to see through the eyepiece. The problem is its proximity to the 4th
magnitude star Kappa Andromedae. It is separated from that beacon by less than one full moon's apparent diameter, and Ross 248's 12th magnitude luster is
totally lost in its glare.
I continue to be amazed that our nearest neighbors
can be so inconceivably faint amidst a sky full of gloriously bright stars.
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