On 22/9/21 9:44 am, Rupert Boleyn - rupert.boleyn at gmail.com (via tml
list) wrote:
>
>
> On 22Sep2021 0432, Alex Goodwin - alex.goodwin at multitel.com.au (via
> tml list) wrote:
>> IIRC, GT:FI also mentions that stars should receive a _bonus_ to their
>> signature (above and beyond their size - eg Sol having +56, Rigel having
>> +67 and Rho Cassiopeiae having +73) from their intrinsic luminosity.
>> Assuming hyperspectral telescopes, I'd expect brown dwarfs to get no
>> bonus, and active stars would get a bonus depending not on their
>> _spectral_ class but their _luminosity_ class (M-class hypergiants
>> getting a bigger luminosity bonus than B-class main sequence stars).
> In that case, the luminosity bonus would be including the size bonus.
> So spotting a star would be a roll vs senor quality (or character
> perception) + luminosity bonus - range penalty. Now it's 'just' a
> matter of getting those bonuses and penalties scaling right...
>
Thankfully, Rupert, at least IMO, GURPS has got that reasonably right,
and was part of the reason I was proposing brown dwarfs as a
luminosity-bonus baseline.

According to el wiki, a difference of 5 magnitudes between the
_absolute_ magnitudes of two objects corresponds to a ratio of 100 in
their luminosities.   Ceteris fnordibus, the brighter object can be
detected 10x further away than the dimmer one - which is +6 to its
signature (combined size + luminosity mod) - thus a unit decrease in
absolute magnitude is a +1.2 on the GURPS scale.

Frinstance, (eyeballing from
https://en.wikipedia.org/wiki/File:HR-diag-no-text-2.svg ), and taking
brown dwarfs as the zero point at abs mag +15, hypergiants (at roughly
abs mag -8) are 23 unit magnitudes brighter, thus meriting a +28
luminosity bonus (and detectable, ceteris fnordibus, 46,000x further
away than a hypothetical same-size brown dwarf).

Sanduleak -69 202, aka Fond Of A Good Banger, aka supernova 1987A's
progenitor, approx 51.4 kpc away, was a blue supergiant until its
catastrophic round of double-parking. 

Blast, I'd galloped on ahead - good point about convolving the bonus.

FOAGB had a radius of 39.6 solar radii, thus meriting an additional +10
for size mod relative to Sol.  Its wiki page notes a relative luminosity
of ~100,000x that of Sol, spread over ~ 1600x more radiating area, for
62.5x luminosity per unit area.  That works out to -4.5 abs magnitudes
on a unit basis, for a luminosity-related signal modifier of +5 (again,
relative to Sol - still trying to find (or cook up) a brown-dwarf
equivalent).

I wonder if that second approach is worth chasing down further?

Alex