Wednesday, June 29, 2016

Ross 248



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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