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BattleTech Player Boards => Fan Fiction => Topic started by: Akjosch on 04 February 2015, 11:46:21

Title: All the pretty stars - Expansion for the AToW:C and IO star system rules
Post by: Akjosch on 04 February 2015, 11:46:21

The current rules of the game wisely limit themselves to just B, A, F, G, K and M-class stars, and outright ignore giants and variable stars in favour of playability. Even the inclusion of B-class stars is kinda a stretch - those don't live nearly long enough to create proper planets of their own. Sometimes though, you just need that "special" one, and that's where I started writing down additional notes.

Brown dwarves: L- and T-class stars

Straddling the divide between "proper" stars and gas giants sit the dark brown dwarves. Too light to ignite pure hydrogen fusion in their cores, they nevertheless produce some light, even though it's mostly in the deep IR spectrum. Spectrographically, they are easy to discern from their bigger M-class brethren by the presence of lithium lines in their spectra - an element which gets "burned" with atomic hydrogen in proper stars in the first 100 million years of their existence or so.

Brown dwarves are, despite their mass, only about the size of Jupiter or slightly larger. As they age, which they do only very slowly, they become colder, less luminous and slightly smaller. They cease deuterium fusion at the transition from L- to T-class and finally go nearly dark after hundredths of billions of years - far in the future of our universe. On the other hand, the more massive of them can manage to ignite into "proper" M-class stars if they are partners of a larger star and siphon off some of its mass.

Rules-wise (since I couldn't find anything else how to calculate those values), their spectrum means that the minimum safe jump distance is limited not by luminosity or radius, but by gravity alone. Recharge times are calculated as the ones at the M9 star, multiplied by how much less irradiance the JumpShip experiences at that distance from the star. In general, it's wiser to just burn fusion reactor fuel instead of waiting for the solar sail to recharge the K-F core, especially at the darker stars where the times easily go into weeks, sometimes months.

I set up the distance to be uniformly at a point where the gravity reaches 180 micro-g. The life zone radii were calculated for a "white" planet (albedo: 0.4) at 310 K (37°C, 98°F) as the inner radius limit and a "dark" one (albedo: 0.1) at 220 K (-53°C, -64°F) as the "outer" one, allowing for the greenhouse effect to raise it to somehow survivable temperatures.

L-class brown dwarves

Ranging from about 13 Jupiter masses (the point where deuterium fusion through gravitational compression starts to be possible) up to about 80 Jupiter masses (where atomic hydrogen ignites in a fusion fire), the unassuming, deep red stars often play the role of satellites to bigger, more easily visible stars. That said, as often as not they are hosts to a planetary system of their own - in some cases even with gas giants. Such "dark" systems are a common find all around the galaxy. Less likely is to find a terrestrial planet inside their life zone: The zones are extremely narrow and even the slightest eccentricity will mean that the planet spends a good part of its orbit being a frozen wasteland or a burning inferno - and sometimes both.

Spectral Class	Charge time	Transit time	Safe jump distance	Habitability mod.	Inner life zone	Outer life zone	Mass (solar)	Temperature	Luminosity (solar)
L9	210 days	1.31 days	31,262,503 km	-9	0.004 AU	0.009 AU	0.013 M☉	1300 K	0.000006 L☉
L8	151 days	1.33 days	32,442,633 km	-8	0.005 AU	0.011 AU	0.014 M☉	1410 K	0.000009 L☉
L7	97 days	1.35 days	33,581,315 km	-7	0.005 AU	0.013 AU	0.015 M☉	1520 K	0.000015 L☉
L6	74 days	1.44 days	37,794,523 km	-7	0.006 AU	0.015 AU	0.019 M☉	1630 K	0.000025 L☉
L5	61 days	1.49 days	40,668,992 km	-6	0.007 AU	0.018 AU	0.022 M☉	1740 K	0.000035 L☉
L4	48 days	1.57 days	45,054,062 km	-6	0.008 AU	0.020 AU	0.027 M☉	1850 K	0.000055 L☉
L3	38 days	1.62 days	48,276,182 km	-5	0.010 AU	0.023 AU	0.031 M☉	1960 K	0.00008 L☉
L2	30 days	1.70 days	52,741,556 km	-5	0.011 AU	0.026 AU	0.037 M☉	2050 K	0.00012 L☉
L1	26 days	1.78 days	58,164,544 km	-4	0.012 AU	0.030 AU	0.045 M☉	2180 K	0.00017 L☉
L0	22 days	1.87 days	64,303,323 km	-4	0.014 AU	0.033 AU	0.055 M☉	2290 K	0.00025 L☉

T-class brown dwarves

Lacking even the mass necessary to ignite deuterium fusion, those are the failed stars. In a lot of aspects, they are simply bigger gas giants - including an atmosphere full of water vapour, carbon monoxide and methane. However, they are still barely above the size of Jupiter despite being at least ten times as massive, and they are still generating heat and light, slowly releasing what was stored during their creation inside their cores and cooling down as billions of years pass by.

Due to the strong absorption of green light in the atmospheric compounds of sodium and potassium, they appear a dark shade of magenta to the naked eye.

You can't really expect life around those stars, but they can give off just the right amount of additional IR radiation to heat up planets orbiting it to "habitable" levels when they are themselves satellites to bigger stars, just outside the life zone.

Spectral Class	Charge time	Transit time	Safe jump distance	Habitability mod.	Inner life zone	Outer life zone	Mass (solar)	Temperature	Luminosity (solar)
T9	37206 days (a bit over 100 years)	1.21 days	26,865,052 km	-10	0.000 AU	0.001 AU	0.0096 M☉	500 K	0.000000025 L☉
T8	23738 days	1.22 days	27,143,454 km	-10	0.001 AU	0.001 AU	0.0098 M☉	550 K	0.00000004 L☉
T7	13842 days	1.22 days	27,419,029 km	-10	0.001 AU	0.002 AU	0.0100 M☉	600 K	0.00000007 L☉
T6	8985 days	1.23 days	27,691,862 km	-10	0.001 AU	0.002 AU	0.0102 M☉	650 K	0.00000011 L☉
T5	5598 days	1.24 days	27,962,033 km	-10	0.001 AU	0.002 AU	0.0104 M☉	700 K	0.00000018 L☉
T4	2935 days	1.24 days	28,229,618 km	-10	0.001 AU	0.003 AU	0.0106 M☉	800 K	0.00000035 L☉
T3	1495 days	1.25 days	28,494,691 km	-10	0.002 AU	0.004 AU	0.0108 M☉	900 K	0.0000007 L☉
T2	889 days	1.25 days	28,757,320 km	-10	0.002 AU	0.005 AU	0.0110 M☉	1000 K	0.0000012 L☉
T1	558 days	1.27 days	29,403,633 km	-10	0.003 AU	0.006 AU	0.0115 M☉	1100 K	0.0000020 L☉
T0	333 days	1.28 days	30,036,042 km	-10	0.004 AU	0.009 AU	0.012 M☉	1200 K	0.0000035 L☉

(Next on the "todo" list: O-class stars and white dwarves)

Title: Re: All the pretty stars - Expansion for the AToW:C and IO star system rules
Post by: Giovanni Blasini on 05 February 2015, 19:38:00

Tagging this to come back when I'm not on my phone. :)

Title: Re: All the pretty stars - Expansion for the AToW:C and IO star system rules
Post by: NullVoid on 09 February 2015, 14:43:00

This is great, but maybe it should be under Fan Design and Rules (http://bg.battletech.com/forums/fan-designs-rules/)?

Title: Re: All the pretty stars - Expansion for the AToW:C and IO star system rules
Post by: snakespinner on 10 February 2015, 02:33:36

Tag