CT Only: Stellar Masking

[Carlobrand]

I confess this is the opposite of what I expected to happen when a star moves off the Main Sequence to Giant phase. For instance, Heya, in the Marches in Regina subsector is an Ag world that orbits a K6 III orange Giant. I’ve been playing for years that millennia ago Heya was a frozen world like Europa or Enceladus and the star’s expansion to Giant phase shifted the HZ outward, immolating the old HZ and thawing out Heya, releasing the budding ecosystems locked under the ice.

Running the numbers with stellar data approximated from GURPS First In, I get an orbital period of over 50 years, creating some interesting flora and fauna life cycles, as well as an interesting and different culture to interact with.

Of course (back to the OT) TL 5, star port B Heya is, under this paradigm, several days’ travel inside the star’s jump shadow for 2G ships, almost a week for 1G vessels... on the coreward Imperial border where many Vargr raiders prowl.

If I am mistaken about how stars leave the Main Sequence and their energy output when they do so, well... Heya’s too much fun to “fix” IMTU.

I suspect the habitable zone moving in relates to the M5 II putting out a lot less energy than the blue-white. Other than that, I can't speak to the accuracy of the Book-6 info. Beyond the basics, I'm not real knowledgeable about stellar mechanics. I would have figured a blue white of that size to supernova. I don't know how a 16 solar mass M5 II would form from a main sequence star.

I believe the 100D limit and the "cube root" being referred to has to do with the gravitational tidal force.

G-Field (Gravitational acceleration):

• a_g = -GM/R² (in mks-units, divide by 10 for units in g's)

Tidal acceleration:

• T_g = ∆a_g = D x -GM/R³, where D is the length (or diameter) of the object experiencing the tidal force. (in mks-units, divide by 10 for units in g's per meter)

So in this interpretation, it is not necessarily the g-field itself that is the problem, but rather the change in intensity of the field with respect to distance across the dimensions of the ship (i.e. the gravitational gradient). This also means that an accelerating ship would potentially have no problem jumping (as the acceleration would potentially be the same at any point on the ship under acceleration). See: Equivalence principle.

That's the one!!

 

[whulorigan]

I suspect the habitable zone moving in relates to the M5 II putting out a lot less energy than the blue-white. Other than that, I can't speak to the accuracy of the Book-6 info. Beyond the basics, I'm not real knowledgeable about stellar mechanics. I would have figured a blue white of that size to supernova. I don't know how a 16 solar mass M5 II would form from a main sequence star.

An M5 II is a Red "Bright Giant", which means that it is already post main-sequence. The Main-Sequence star that it evolved from would have been a B-class (or possibly early A-class) main sequence (Type-V), which would have been smaller with a hotter surface/photosphere. As the Blue main-sequence used up its fuel, it slowly evolved onto the giant branch (Type IV --> Type III --> Type II) growing larger while its surface/photosphere expanded and cooled from B (Blue-white) down to M (Pink-orange).

Also note that as the star expands and loses mass over time, its planets will slowly move into more distant orbits due to the lower gravitation.

The M5 II will eventually supernova.

 

[Carlobrand]

An M5 II is a Red "Bright Giant", which means that it is already post main-sequence. The Main-Sequence star that it evolved from would have been a B-class (or possibly early A-class) main sequence (Type-V), which would have been smaller with a hotter surface/photosphere. As the Blue main-sequence used up its fuel, it slowly evolved onto the giant branch (Type IV --> Type III --> Type II) growing larger while its surface/photosphere cooled from B (Blue-white) down to M (Pink-orange).

Also note that as the star expands and loses mass over time, its planets will slowly move into more distant orbits due to the lower gravitation.

The M5 II will eventually supernova.

So it does go boom, just later. How pronounced is the orbital movement? How much time are we talking between M5 II and kablooey?

 

[whulorigan]

So it does go boom, just later.

If the stellar core is greater than ~ 1.40-1.44 M_Sol , it will eventually go boom.
See: Chandrasekhar limit

1. Wikipedia: https://en.wikipedia.org/wiki/Chandrasekhar_limit
2. Cosmos @ Swinburne University: http://astronomy.swin.edu.au/cosmos/C/Chandrasekhar+Limit

How pronounced is the orbital movement?

I am not sure the astronomers are entirely sure. One of the reasons why it is difficult to predict the eventual fate of the Earth is that they don't know just how big of an effect there will be. Back in the 1970's, the estimate was that the swelling sun would engulf the inner Solar System at least to the orbit of Mars. Today, the debate is to whether or not it will reach the eventual Earth orbit, and/or whether or not Earth will be vaporized, or just rendered an airless rockball inferno.

How much time are we talking between M5 II and kablooey?

Uncertain, but probably on the order of 100,000 years or so, give or take. (It could be much less if it has been on the Giant Branch of the HR-Diagram for a while already).

 

[Straybow]

At one time Aramis proposed this idea where the 100-diameter limit evolved from the cube root of some function or another. I wish I could recall the details; I thought it was rather clever.

Here's the full treatment: StuffOnline (Jump Drive)

 

[BRover]

NO WAY!


The list of travel times for mainworlds in the post linked by Xerxes is off by ORDERS OF MAGNITUDE!


A transit of 1 billion km takes only 7.3 days at 1G. Menorb, for example, is listed as taking 66 days. That would be 81 billion km, or 541 AU. How big did the list maker think Menorb's primary was?


Menorb is K2 V (typically ~0.8 Msol, 0.735 Rsol) which makes the 100.5 diameter jump shadow roughly 103M km. At 2√(D/A) that makes 1G (10m/s²) travel time 56.4 hours (not days) to reach the star. Hab zone edge is approx 0.35AU = 52M km for a differential of only 51M km. Travel time at 1G is only 39.7 hours.

Actual travel time will be less than that. . . .

This was my first thought. I looked up the data on the four 66 day systems, noted that three (at least) were dim-ish main sequence stars, and wondered where he got those travel times. (My pre-research thought had been to wonder how many of the stars in question were giants. No, they weren't.)

I just did a few in-my-head rough calculations, especially since (up to the 4-week manuver-drive LBB limit) M-drive produces acceleration of 1G (to 6G), and distance = 1/2 * a * t^2, so doubling the time roughly quadruples the distance. So in 66 days, you should be able to get from here to the Voyager spacecraft, much less Neptune--and escaping a solar mask should be more like 66 hours (or less) than 66 days.

So, I'd been hoping the data was helpful--but it proved more a distraction than helpful.

Most main sequence stars, to escape the habitable zone, I'm thinking--not having done the precise math--if the h-zone is in the 100-diam-zone, the distance should be on the order of a fraction of an AU, likely under 0.4 AU (WAG) = 60M km, which is 40-50 hours at most.

ETA: I see this list was made by using older (CT) stellar data, with many more giant stars (class I-II-III), which explains much of the problem. The next question is searching to see if that data is available anywhere. . . .

 

[fridge]

Menorb's primary used to be an M5 II, according to the old Spinward Marches Campaign. I suspect it was changed for precisely that reason. The giants made a royal mess of things when people started talking about stellar masking. They changed Cogri too, used to be an M1 II.

Correct. The original table was mine. it was part of a discussion with Marc and Don for the T5 Second Survey as to why the Giant stars were breaking canon with Stellar masking applied as the travel times were never considered when things were written about the systems - it was change the star type or throw out everything written for the system or remove stellar masking - Marc's call was to change the stars. From memory if other canon was not going to be impacted by the Giant stars they stayed.


The table is thus no longer relevant as the stars were changed in T5SS. Would have helped if the other columns were also included with what stars they were based on, for context.

 

[BRover]

Here is fridge’s table, with star data included:

"Based on the assumption the mainworld orbits the primary star in the habitable zone and any companions are Outer Companions, the following systems are Jump Masked by the Primary Star. Third column gives how long dd:hh:mm:ss it takes from a standing start at minimum range where you come out of jump to accelerate at 1g, turn over and decelerate at 1g to reach the mainworld. Yes those top ones are 66 days!!!

"There are some interesting planets in the list that may (or may not) have an effect on "canon". Menorb and Narsil spring to the eye immediately."


0723 Trifuge 66:07:30:02 M5 II
1803 Menorb 66:07:30:02 M5 II
1924 Ianic 66:07:30:02 M6 II M9 D
2232 Crout 66:07:30:02 M7 II M9 V
1216 Stellatio 46:21:21:39 M9 III
1402 Farreach 46:21:21:39 M3 II M0 V
1102 Riverland 33:03:45:01 M7 III
1131 Faldor 33:03:45:01 M7 III
1204 Mongo 33:03:45:01 M6 III M0 D
1212 Digitis 33:03:45:01 M6 III
1529 Steel 33:03:45:01 M8 III
2933 Raydrad 33:03:45:01 M7 III M9 D
2935 Murchison 33:03:45:01 M5 III M9 V
0927 Narsil 30:16:43:18 M0 II M6 D
2419 Cogri 30:16:43:18 M1 II
1337 Judice 21:16:56:27 M3 III
1733 Lydia 21:16:56:27 M4 III M0 V
2134 Caledonia 21:16:56:27 M4 III M0 D
2411 Keanou 21:16:56:27 M3 III M2 D
2936 Hammermium 21:16:56:27 M3 III
1909 Hefry 17:17:20:47 K6 II M6 V
2402 Heya 15:08:21:39 K6 III M8 D
0115 Xhosa 12:12:45:55 M0 III
1116 Frenzie 12:12:45:55 M2 III M3 D
1934 Weiss 12:12:45:55 M0 III M2 D
2701 Lablon 12:12:45:55 M2 III M4 D
2940 Thornnastor 12:12:45:55 M1 III
3021 Brodie 12:12:45:55 M1 III M7 D
3114 Huderu 12:12:45:55 M0 III
0101 Zeycude 1:06:41:48 K9 V
0129 Uniqua 1:06:41:48 K9 V M9 D
0421 Zamine 1:06:41:48 K9 V
0518 Faisal 1:06:41:48 K9 V M7 D
0710 Stave 1:06:41:48 K9 V M2 D
1018 Choleosti 1:06:41:48 M3 V M4 D
1138 Tarsus 1:06:41:48 K9 V
1515 Calit 1:06:41:48 K9 V M5 D
1739 Aster 1:06:41:48 K9 V
1935 Windsor 1:06:41:48 K9 V M0 D
2036 Glisten 1:06:41:48 K9 V
2309 Yurst 1:06:41:48 K9 V
2406 Moughas 1:06:41:48 K9 V M9 D
2415 Vreibefger 1:06:41:48 K9 V
2418 Icetina 1:06:41:48 K9 V M8 D
2720 Loneseda 1:06:41:48 K9 V
3004 Zykoca 1:06:41:48 K9 V
3008 Pysadi 1:06:41:48 K9 V M1 D
3035 Prilissa 1:06:41:48 K9 V

I’m not entirely sure of the star data--but it seems consistent. Note, for example, the Dwarf stars have the spectral class and number, which was later (but pretty early) dropped, IIRC.

 

[Grav_Moped]

Looks like Judice (SM 1337) got tweaked from an M3 V to an M3 III. Well, there goes part of a scenario I was working on... LOL

Part of it hinged on Judice not only having a particularly nasty atmosphere, but also being "in the hole" of the star's gravity well. NOBODY would stop there if they didn't have to! Instead, there's a far-port at the star's 100D limit to refuel ships passing through and of course there's a gas giant for the skimming. Made Research Station Theta that much more isolated.

It's not Travel Zoned, but who'd bother going in?

 

[BRover]

Travellerrpg.com indicates the following giant stars (some are in multiple star systems) in the Marches:

1204 Mongo M6 III
1402 Farreach M3 III
1909 Hefry K6 II
2402 Heya K6 III
2701 Lablon M2 III
1116 Frenzie M3 III
2411 Keanou M3 III
1825 Zaibon M6 III
3021 Brodie M1 III
1732 Lydia M4 III
1932 Mithras M2 III
2134 Caledonia M4 III
2232 Crout M7 III
2933 Raydrad M7 III
2935 Murchison M5 III

I got these simply by pulling up the sector data (Milieu 1116, but that shouldn’t matter . . .) and searching for ii. As it happens, no names or other data had that sequence, so the 16 occurrences were all for giant stars. I suppose Ia or Ib stars might be missed, but they should be vanishingly rare.

Gravity_Moped, You could always tweak Judice's star back to the giant--and have the reason the research station is there is that they need to be in orbit around a giant, perhaps some particular quality of flares or size or something that it has to be THERE, as opposed to, say, Mithras' system (1732). Or else have a research station (secret? auxiliary facility?) on Mithras?

 

[Grav_Moped]

Travellerrpg.com indicates the following giant stars (some are in multiple star systems) in the Marches:
<snip>

I got these simply by pulling up the sector data (Milieu 1116, but that shouldn’t matter . . .) and searching for ii. As it happens, no names or other data had that sequence, so the 16 occurrences were all for giant stars. I suppose Ia or Ib stars might be missed, but they should be vanishingly rare.

Gravity_Moped, You could always tweak Judice's star back to the giant--and have the reason the research station is there is that they need to be in orbit around a giant, perhaps some particular quality of flares or size or something that it has to be THERE, as opposed to, say, Mithras' system (1732). Or else have a research station (secret? auxiliary facility?) on Mithras?

The research station is at least overtly to study the life forms living in the corrosive atmosphere, in canon. The atmosphere itself is still useful as a barrier, since most captains won't risk hull damage to go dirtside (the research station has shuttles with specialized corrosion-resistant hulls). So, having the planet jump-masked isn't critical to the scenario -- it's just a nice extra touch.

Mithras has a prison... also something that benefits from being "in the hole" of jump masking.

Many worlds imply their own unique stories just in the wiki write-up, aside from published scenarios. The implicit "story" for Judice is that the researchers either just found something really interesting, or there's something else going on there too. Maybe both!