Expert: Tom Whiting - 3/25/2010

Question
We are studying the evolution of brightest stars in a constellation. I have to do a star report. We had to choose a star out of a constellation. I chose the Delta Crateris. I have to know when my star was born and what my star was before this time, but I can't find any information on it, I don't know where to look for it, I need help please do you know this information.

Answer
Hi Helen,
I couldn't find much on it either on the internet.... my best try was at
http://stars.astro.illinois.edu/sow/deltacrt.html
I did notice that Wikipedia has the distance all wrong at 9000 ly... if a K0 spectral type
sub-giant at 2.5 solar masses was at that fantastic distance, it would be way below our naked-eye limit. The more correct distance is given on other sites at about 195 light years.
You can google still more sites, but you won't find much on that star or that constellation,
because it is one of the most non-descript and dimmest areas of the sky, PLUS there just isn't anything much of interest in that constellation (like Deep Sky Objects, variable stars, double
or multiple stars, etc) so most of us astronomers just don't go to that area of the sky very often... there isn't much "interesting" to see in the first place.

Just curious, of all the "bright star" constellations... there are over 20 of them that have
a very bright first magnitude star or brighter... why Crater(?), a very insignificant constellation and area of the sky?  Personally, I would change and pick among the following:   Deneb in Cygnus, or Antares in Scorpius, Vega in Lyra, Altair in Aquila, Regulus in Leo, Spica in Virgo, Fomalhaut in Piscis Austrinus, Capella in Auriga, Castor or Pollux in Gemini, Procyon in Canis Minor, Aldebaran in Taurus, Rigel in Orion, Sirius in Canis Major, etc....OR,
If you really don't like 1st magnitude stars, then at least pick a constellation that we can all, at least, easily see!  (Crater is barely visible with any light pollution).  Take Alpha Andromedae in Andromeda, Alpha Persei in Perseus, Alpha Pegasi in Pegasus, Alpha Ceti in Cetus, and I can go on and on; all of these are at least easily visible with the naked-eye at 2nd magnitude.  And they are located in much more interesting constellations too!
AND since these are brighter, closer, and easily visible stars, there is typically much more information on these brighter stars of these constellations (areas of sky).

But if you really want to stick with Alpha Crateris, all I can establish is that since it's mass
is 2.5 solar masses, and it's already in the red giant phase fusing helium nuclei to carbon nuclei in it's core, it's certainly a least a couple billion years younger than our sun (4.6 byo) and has a much shorter lifespan, maybe one billion years total lifespan, if it's lucky! We also know that it's not massive enough to go supernova, so eventually it will go the same route that our sun will someday; after a relatively short red giant phase (couple of tens of millions of years) of fusing 3 He nuclei to one Carbon nuclei, the Triple Alpha fusion process, the core collapses as the star forms a planetary nebula, all fusion reactions are finished, as the core cannot increase it's temperature to 600 million degrees to start the next round of fusion reactions, namely Alpha Capture fusion reactions, because there isn't enough mass to do this... so the dust and gas of the planetary nebula will slowly dissipate, and you are left with a little white dwarf star in the core.  Which will eventually cool to a black dwarf star. The star probably started with about 2.5-3.0 solar masses so it was probably initially an A or F spectral type main sequence star using mainly the faster and more efficient CNO fusion cycle during it's one billion year lifespan.  (As opposed to the sun's Proton-Proton Chain fusion reaction methodology).  There are currently no known extra-solar planets revolving around this single star as far as I know, and the odds that if there are, there was not enough time to evolve carbon-based life anyway... star would have had too short a lifespan.  Realize that these are just educated guesses I have for your star.  

Pick a non-descript 3.56 magnitude single star and you get a just a little non-descript information.  Pick a bright 1st magnitude star, and you'll probably find lots of stuff about it on the internet.  Your choice.
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA  

FOLLOW UP:
Opps.... I meant to say, in 3rd paragraph, first sentence, "If you really want to stick with Delta Crateris..."  and not Alpha Crateris.
Tom