Wednesday, June 1, 2016

Ross 154

Also known as TYC 6859-1332-1, AC-24 2833-183, GCTP 4338, GJ 729, HIP 92403, LHS 3414, V1216 Sagittarii, Proxima Sagittarii
     From the very beginning of the scientific age, mankind’s explorations of the Heavens, as well as our more recent first steps in the physical exploration of them, have been largely motivated by the quite understandable quest for life beyond our own planet. It certainly provided much early impetus for the painstaking telescopic reconnaissance of the solar system from Galileo all the way to Sputnik. Always the hope lay just under the surface (and occasionally right atop that surface) of discovering some sure sign of life on the Moon, Mars, Venus, or even Mercury; whether it be lunar cities (Gruithuisen), Martian canal-builders (Lowell), Venusian swamp monsters (Arrhenius), to swarms of lunar insects (Pickering), or yet more ultimately improbable ideas.

The Canals of Mars, as envisaged by Percival Lowell

     Even in the Space Age, the Search for Life has generally been at the forefront of our extraterrestrial endeavors. The Viking landers were specifically designed to look for telltale signs of organic processes on the Martian surface. The Pioneer, Voyager, Galileo, and Cassini missions all had the identification of possible biospheres elsewhere among the outer planets on their agendas. Even when not formally an objective, the first question always asked (at least by the public) when a new world had been revealed by a visiting spacecraft was invariably “Is there life?”
     This obsessive desire to answer the question “Are we alone?” has continued right into the now technologically-enabled search for worlds outside of our own solar system – the so-called “exoplanets”. The Kepler Space Telescope, which has revealed the existence of literally thousands of new planetary systems, only rises to the public consciousness when claims are made that the latest discovery may possibly be an “Earthlike” world, with interest invariably falling off as the “yes, but” qualifiers start coming out in the press releases.
     Well. There can be no such hopes for the next target on our list. For we have not so far in our observational journey through the Solar Neighborhood come across such an inhospitable star, such an implacably hostile environment to life as we know it, such a less desirable piece of real estate as Ross 154.
     In many respects, Ross 154 is yet another commonplace red dwarf, similar in many respects to the five others we have thus far tracked down. With 17% of the Sun’s mass and 0.38% of its luminosity, it is a typical star of stellar class M3.5V. Its diameter of approximately 24% of the Sun’s measurement is also no surprise. And as is so common among stars of this classification, it is also a flare star. But what a flare star! They can occur on Ross 154 as often as once every 48 hours, and can measure as much as 125,000 miles across (one-fifth of the star’s circumference). Their intensity increases toward the blue end of the spectrum, and the star’s overall visual magnitude can increase during such an episode by as much as 3 to 4 magnitudes. They are even stronger in the ultraviolet wavelengths, and the associated X-ray emissions are more than 10,000 times as strong as similar flare episodes on the Sun. Just imagine the effects on a planet within the “habitable zone”, which for Ross 154 is centered at approximately 0.022 AU out. Any potential biosphere would be regularly sterilized. No, Ross 154 will be no place to search for life.
     Otherwise, Ross 154 differs in significant ways from those we have previously tracked down. For one thing, it is relatively young – perhaps not quite a billion years old. For another, it does not possess any notable velocity relative to the Sun, and orbits the Milky Way’s core entirely within the galaxy’s “thin disk” (see the section above on Lalande 21185). The star’s orbital eccentricity is 0.052, which means its distance from the center of the galaxy varies from 27,000 to 31,000 ly. (The Sun’s orbit takes it from 25,000 to 28,000 ly from the galactic core.) At present, Ross 154 and the Sun are gradually approaching each other, and will continue to do so for the next 157,000 years (at which point they will be separated by a little more than 6 light years). After that time, their respective orbits will cause the two stars to move further and further apart for the next 100 million years or so, by which time we will be separated by thousands of light years. So, despite the similarity in orbits, it is sheer coincidence that we are as close to Ross 154 as we currently are.
     No companions of planetary or any other nature have been either observed or suspected about Ross 154 which, given the unfavorable conditions described above, is probably just as well.

Observing Ross 154

   When I first approached the task of tracking down Ross 154, I did so with not much optimism. First of all, its location in the constellation Sagittarius did not bode well. I imagined a Needle in a Haystack search for an anonymous point of light amidst the rich star fields of the Summer Milky Way. Secondly, the star’s southerly position of declination -23º 50’ 10” was not at all promising. (On our list, only the impossible WISE 1541-2250 lay further south.) From my usual observing site at Howard County’s Carrs Mill Park, the similarly situated M22 globular cluster (quite close to our search area, with a declination of -23º 54’ 12.2”) scarcely clears the tops of the trees in that direction. Add to that the fact that I would have to contend with the light pollution from Washington, D.C. in that direction, and it looked like uphill odds all the way.
     But Ross 154 did have a few items in its favor, which I thought might help in my search. Its relatively bright magnitude (for a red dwarf) of 10.43 meant it wasn’t (like DX Cancri) out of the question for my equipment. Next, when I actually checked out its precise location in my Uranometria 2000.0 Deep Sky Atlas, I found to my relief that it was nowhere near the dense star clouds that fill so much of Sagittarius. In fact, it was smack in the middle of an area of that constellation so devoid of stars that I feared I’d be facing the opposite problem – that of having no convenient guide points from which to star hop.
     But as it turned out, that last problem turned out to be not so great an issue after all. As can be seen in the above star chart, Ross 154’s position directly north of the Teapot’s handle makes a convenient starting point for our search. Draw an imaginary line between 3rd magnitude Lambda Sagittarii (the top of the Teapot) and 5th magnitude Nu Sagittarii (of no particular asterism), and our target lies close to the left end of that line. For a moment, concentrate on the star Nu Sagittarii (a.k.a., 32 Sagittarii, which is what I’ll be calling it from here on out, to avoid confusion with a nearby 5th magnitude star which shares the “Nu” designation, the two stars going by Nu1 and Nu2). This star is traditionally taken to be the eye of the archer for which the constellation is named. (In fact, its proper name, Ain al Rami, is Arabic for “Eye of the Archer.”) Slowly scan eastward in the direction of Mu Sagittarii (see star chart just below this paragraph) until you come across another 5th magnitude star, 28 Sagittarii. This particular star was the cause of much excitement among planetary scientists on the night of July 2-3, 1989, when it was occulted by both Saturn and its largest moon, Titan. This was, of course, many years before the Cassini spacecraft gone into orbit about the ringed planet, so this was the scientific community’s best opportunity to date to measure and determine the chemical composition of the atmospheres of those two bodies. And of course it gave many an amateur astronomer the thrill of a lifetime, observing the star pop out amidst the rings as it traversed the Encke Gap and Cassini division.

     Once you identified and admired these two stars, imagine a line connecting the two. Then further picture a roughly equilateral triangle extending southwards, towards the Teapot’s Handle. At the third point of this triangle, we will find our goal.
     Here is where things will get difficult. There are no stars in this region even close to naked eye visibility. In fact, the brightest luminary in the vicinity is the paltry magnitude 9.3 star HD 174312 (see star chart below this paragraph).  This makes a neat little isosceles triangle with two nondescript 11th magnitude stars (among the brightest lights around in this benighted region). If you can spot this triangle, you will have no trouble at all capturing magnitude 10.43 Ross 154.

     On the opposite side of Ross 154 from this triangle, you should be able to pick out a curious bow tie asterism of stars of magnitudes averaging roughly 10.5. As you can see in the above star chart, our target is pretty much at the midpoint between these two stellar groupings.

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