Celestia Forums

I'm looking for info on the Spica star system, which sounds rather interesting.

I found this: http://www.astro.uiuc.edu/~kaler/sow/spica.html

but is there any more info about the last sentence there:

"Lunar occultaions yeild evidence that Spica is in fact multiple, with three other fainter components."

So we know that Spica consists of two Type B main sequence stars, but is this implying that there could be more? Is anything known about these other companions? Are they spectroscopic or are they beyond the main binary pair?

Also, given that Spica is a strong X-Ray source, would this radiation sterilise the space for a few parsecs around it? I'm wondering (for the scifi RPG that I participate in) if nearby stars could have earthlike planets with life on them, or whether there'd be too much radiation from Spica to allow that to happen.


Can anyone shed any (preferably not UV-rich) light on this?

Evil Dr Ganymede wrote:Also, given that Spica is a strong X-Ray source, would this radiation sterilise the space for a few parsecs around it?

Don't think so. The Sun has an X-ray luminosity of around 1e20 watts. According to Allen's Astrophysical Quantities, even late O or early B supergiants (Zet Ori, Eps Ori) pump out only around 2e25 watts in X-ray wavelengths, and a late B main sequence like Algol only 5e23 watts.
So even if the Spica pair put out 1e25 watts of X-rays between them (100,000 Suns), you'd only need to back off to 300AU or so before the inverse-square law had you down to an Earth-like level of irradiation. The effect would be trivial in neighbouring solar systems.

Grant

Ta, grant....

Presumably there's no further information on the extra companions that Spica may have? Even things like what spectral type they are and roughly how far away they are would be useful...

Oh Evil One,

I did some Web searches and couldn't find anything useful. I fear it'll take a formal search of the literature, including using some of the subscription-only sites, to find the information you want.

That's odd... I couldn't find anything about multiple stars around Alpha Virginis on Web of Science - I don't even know whether it's a recent discovery or not, and I dunno any references for the claim...

http://www.alcyone.de/SIT/mainstars/SIT000832.htm

claims it has 5 components. and references
Worley (1978) and "The Washington Visual Double Star Catalog, 1996.0 (Worley+, 1996)". It also includes the vague statement "occultations yield three companions" but no references for that information.

Here are some citations I came across. I dunno if what info they may contain about the total number of members.

LYUBIMKOV, L. S., RACHKOVSKAYA, T. M., ROSTOPCHIN, S. I., TARASOV, A. E.,The
binary system alpha Vir (Spica) : fundamental parameters of the components and
differences in their helium abundance., 1995, AZh, 72, 212

JORDAN, J.; DUKES, R.; MILLS, L., APT Observations of the Former Beta Cephei Star
Spica, 1997, AAS, 190, 2607

(supposedly its Cephid oscillations have increased again since this publication)

Thanks... er, do you know what journal "AZh" is?

According to http://adc.gsfc.nasa.gov/adc/other_jrl_holdings.html

It's
Astronomicheskij Zhurnal (AZh)

Their home page is at
http://www.maik.ru/cgi-bin/journal.pl?n ... &page=main

Ta... Nuts, although I can actually access that journal online, I can only get to the abstract of the aforementioned paper online... and that doesn't mention other companions.

I'd imagine that these companions must be somewhat distant from the main pair if they're (possibly) only noticed by lunar occultation, right?

Here may be something:

2432 high resolution optical and infrared observations of 1625 sources, from interferometry and lunar occultation (Richichi & Percheron 2002).

which I haven't located yet, is mentioned in

"Astrophysics in 2002" ( Trimble and Aschwanden)
http://www.journals.uchicago.edu/PASP/j ... 03051.html
(subscription required)

Trimble and Aschwanden's writing style, presumably to offset the dryness of the topics, is rather amusing.

Here you go, from Kaler's book The Hundred Greatest Stars:

...B5 and B7 stars at distances of 4 and 40AU from the pair, and a 12th magnitude K dwarf over 10,000AU away (if it is a member at all).

Grant

Evil Dr Ganymede wrote:I'm wondering (for the scifi RPG that I participate in) if nearby stars could have earthlike planets with life on them, or whether there'd be too much radiation from Spica to allow that to happen.

I think you should put a habitable planet around the distant K dwarf ... its magnitude would make it around K5V.
It would certainly have an excellent view of the four B stars in the Spica system. If we assume for the moment that the measured plane-of-sky separation reflects real orbital distances, then the inhabitants of a planet around the K dwarf would see:

The central pair and the inner B companion merged into a single brilliant star of magnitude -15: eight times the full moon and easily visible in daylight. About once a year the inner B companion might creep far enough out of the glare to appear as a separate star of magnitude -13, maximum separation about 1.5' ... a fair test for visual acuity. The outer B companion would amble in a 50 year orbit as a -12 mag star, maximum separation from the others of a quarter-degree.

Pretty.

Grant

So we have a close binary B V pair, a B5 V at 4 AU, a B7 V at 40 AU, and the K V far companion, right?

It would be rather interesting to put the world around the K V, wouldn't it... presumably it's well out of the range of nasty radiation emitted by the B stars. A distant companion might be more likely to be older than the B stars too (and thus have planets around it) - perhaps it's captured. I'd hate to be there in a few million years though, when the B stars started exploding! :0

Given we'd have three - maybe four - stars at below -10 magnitude in the sky, would that pretty much turn night into day on the planet around the K star? That's got to dramatically improve visibility at night, surely.

It's odd that I've still not found any solid confirmation of the existence of these companions anywhere though (other than the quote that Grant added here). Are they actually confirmed or suspected? (I guess I can assume they're confirmed for the purposes I'm after).

I found the PASP paper that Selden linked to - while it doesn't really contain any information on Spica, I must agree that it's written in a refreshingly entertaining manner.

The system would make an interesting addon to Celestia though...

Evil Dr Ganymede wrote:So we have a close binary B V pair, a B5 V at 4 AU, a B7 V at 40 AU, and the K V far companion, right?

Kaler gives spectral classes of B1V and B4V for the central pair, but sources are very variable. However, if you combine the theoretical absolute mags for B1V+B4V+B5V+B7V, as given by Kaler, it comes out to -3.6, which is pretty much on the nail with the observed -3.55.

Evil Dr Ganymede wrote:It's odd that I've still not found any solid confirmation of the existence of these companions anywhere though (other than the quote that Grant added here). Are they actually confirmed or suspected? (I guess I can assume they're confirmed for the purposes I'm after).

You'll find the B system described and referenced in the data search facility for Alcyone Software (always a handy source of information), with the angular plane-of-sky separations consistent with Kaler's linear measures. VizieR lists the distant K companion as component B, and the multiple B-stars as component A. Again, the angular separation fits with Kaler's information.

Grant

I'm trying to make an SSC of the Spica system... what's the orbital period of the B5 V companion at 4 AU and the B7 V companion at 40 AU? I'm guessing their radii are a little smaller than the innermost B4 V companion?

I guess I'll make it so that they orbit the B1 V itself, I suppose I can't set it so that everything orbits a common barycentre because the B1 V is fixed?

Here's what I got so far...




And can someone remind me if there's a way to stick a lens flare on a planet? (or in this case, a star that's pretending to be a planet ).

...of course, if the B stars are still in the dwarf stage, everything there is probably still undergoing the heavy bombardment stage, as if the X-rays and stuff aren't bad enough...

chaos syndrome wrote:...of course, if the B stars are still in the dwarf stage, everything there is probably still undergoing the heavy bombardment stage, as if the X-rays and stuff aren't bad enough...

I'm assuming the K V star is captured and much older. And it sounds like its out of the range of the nastiest radiation from the B stars.