RE: starship-design: Stars_within_16_light_years_of_the_Sun

[Zenon Kulpa <zkulpa@zmit1.ippt.gov.pl>]

> From: Steve VanDevender <stevev@darkwing.uoregon.edu>
> 
> Zenon Kulpa writes:
>  > Sorry, but this MUST be in error.
>  > Your data gives B farther away than A by 0.5 ps, that is 1.6 ly,
>  > and at the same distance as to Barnard.
>  > And both these are certainly not true.
> 
> I'll have to agree with Zenon on this one.  Alpha Centauri is a trinary
> system, with Proxima being distant from A/B; the apparent distance to
> A and B should be nearly identical.
> 
As one of the sources says, currently it is 23 AU (0.0001 ps - a little farther 
than Uranus from Sun); the minimal distance being half that (11 AU).


>  > I am also including some data from some other sources for comparison below.
>  > Note also differences concerning spectral types and magnitudes
>  > between the sources.
> 
> Lee's chart is also mislabeled; substitute "absolute" for "visual" in
> the heading.
> 
Yes (*).


> The difference in spectral class is likely a difference in opinion.
> Spectral class is judged primarily by the appearance and relative
> strength of sets of spectral lines corresponding to different elements
> and compounds in their various ionization states; these can provide a
> good estimate of the surface temperature of the star, as well as the
> abundance of the elements involved.  Several components of spectral
> class are rather subjective and may be interpreted differently by
> different astronomers, resulting in the different subclass numbers. 
>
I wonder - are these differences of opinion so great (K1 vs. K5 or G0 vs. G2 ?).

 
> The 'V' following the spectral type in Lee's chart is the luminosity class
> (most main sequence stars are class V; the classes are roman numerals).
> 
Some sources encode the luminosity class with lower case letters (a, b, c, d, e)
instead of Roman numerals. This is probably the meaning of "e" in the 
spectral type for Proxima.

-- Zenon


>  > NAME                 DISTANCE         SPECTRAL     APPARENT     ABSOLUTE (*)	
>  >                      (ps/ly)          TYPE         MAGNITUDE    MAGNITUDE
>  > L. Parker source:
>  > -----------------
>  > Proxima Centauri       1.3            M6 V         11.05        15.49	
>  > Alpha Centauri A       1.33           G2 V         -0.01         4.37	
>  > Alpha Centauri B       1.83           K1 V          1.33         5.71	
>  > Barnard's Star         1.83           M4 V          9.54        13.22	
>  > 
>  > http://www.essex1.com/people/speer/stars.html:
>  > ----------------------------------------------
>  > Proxima Centauri      (1.29)/4.2      M5e          11.3
>  > Alpha Centauri A      (1.32)/4.3      G0             .33
>  > Alpha Centauri B      (1.32)/4.3      K5            1.70
>  > Barnard's Star        (1.83)/5.96     M5            9.5
>  > 
>  > 
>  > http://monet.physik.unibas.ch/~schatzer/Alpha-Centauri.html:
>  > ------------------------------------------------------------
>  > Proxima Centauri      (1.29)/4.22     M5e 
>  > Alpha Centauri A      (1.33)/4.35     G2 
>  > Alpha Centauri B      (1.33)/4.35     K1 
>  > 
>  > Separation A/B (current): 23 AU = 0.00001 ps
>  > 
>  > The units:
>  > ----------
>  > AU =   149 598 770 km
>  > ly =  9.4543*10^12 km =  63197.7 AU = 0.3066 ps
>  > ps = 30.8361*10^12 km = 206125.7 AU = 3.2616 ly 
>  >