# Thread: Six-star M-dwarf multiple system only 21 lightyears away

1. ## Six-star M-dwarf multiple system only 21 lightyears away

Is Wolf 630 + Wolf 629 a sextuplet star only 21 light years away, made up only of low-mass red dwarfs?

This is a difficult question, as some astronomy papers say yes and some say no, going back into the 1970s-1980s. Here's what I found. Not linking to articles now, these can be found on the SAO/NASA ADS site.

CAVEAT: All of these stars have multiple confusing names, and some papers misidentify the stars badly (e.g., Wolf 629 = Wolf 630).

* Wolf 630 = Gliese (GL, GJ) 644 = HD 152751 = HIP 82817 = V1054 Oph. There is an A component (flare star) and a spectroscopic binary not yet separated (Ba & Bb). All are M3V to M4V.

* van Biesbroeck 8 = Wolf 630 C, a distant sub-size M-dwarf flare star. Once thought a brown dwarf orbited it, false positive. Distant but comoving with AB. M7V.

* Wolf 629 = Gliese (GL, GJ) 643 = HIP 82809, once thought single but apparently now a spectroscopic binary (at least) per SIMBAD, listing both GJ 643 A & B. M3.5V-M4V.

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Studies of multiple stellar systems – IV. The triple-lined spectroscopic system Gliese 644
Tsevi Maze et al. (2001)

DATA: "In this section we discuss two additional stars associated with the Gliese 644 triple system. One of them is Gliese 643 (=Wolf 629, α = 16:55:25.26, δ = −8:19:21.3 [J2000], V = 11.74 mag), at a projected separation of about 70′′ from Gliese 644. The other companion, at a separation of 220′′, is the faint star vB 8 (=Gliese 644C, α = 16:55:35.74, δ = −08:23:36.0 [J2000], V = 16.80 mag). The common proper motion of Gliese 644 and 643 (Wolf 1919) and their similar parallax (e.g., ESA 1997) strongly indicate that they are indeed physically connected. Van Biesbroeck (1961) found that vB 8 also shares with Gliese 644 the same proper motion, attesting to its physical association with the system... The Gliese 644/643/vB 8 system is the nearest known quintuple stellar system."

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Accurate masses and radii of normal stars: Modern results and applications
G. Torres, J. Andersen, A. Gimenez (2009, published 2010)

DATA: GJ 644 A + Bab / HD 152751 [[Wolf 630]] is 6.46 pc away (SIMBAD says 6.5, apparently abbreviating, this is not what original paper says; I check original sources whenever possible)

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Wolf 629 -- Spectroscopic binary (so Wolf 629 is a double star, at least)

distance = 6.4969 pc (cannot get original paper)
2018yCat.1345....0G - CDS/ADC Collection of Electronic Catalogues, 1345, 0 (2018)

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HD 152751 -- Spectroscopic binary (Wolf 630 is a quadruple star, with the innermost system a spectroscopic binary)

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The difference between 6.4969 pc and 6.46 pc is 0.0369 pc, = 7611.17 AU. Seems pretty close to me, plus co-traveling.

Now, Wikipedia (I checked the sources/footnotes) claims V1054 Ophiuchi + Gliese 643 is a quintuple system, but if Wolf 629 is a spectroscopic multiple, then it is a six-star (sextuplet) system. Someone worked VERY hard on this Wikipedia page, a work of love, but it has errors.

PROBLEM: Why is this sextuplet system not better known? What in the above data is incorrect, making this NOT a sextuplet system?

Asking mostly as an interested astronomy hobbyist, but it is confusing. Thank you, anyone who can shed light on this.
Last edited by Swift; 2018-Nov-08 at 05:44 PM. Reason: removed ?

2. Attachment shows earliest mention I can find that this is a six-star system (Walker 1980).

3. Mazeh (2001) did not find Wolf 643 to be a binary but could not disprove it. SIMBAD still calls it a binary, though.

4. The reason I ask about this system is because I've seen mention online that Wolf 630 and Wolf 629 are separate and not gravitationally connected.

Amateur site: http://andys.wikia.com/wiki/BD-08°4352_System

5. I think I found what happened, perhaps. In a 2010 paper, in "UBV(RI)CJHK observations of Hipparcos-selected nearby stars" by KOEN C., KILKENNY D., VAN WYK F. and MARANG F., the following parallaxes were given:

Wolf 629 measured at 6.72 +/- 0.18 pc and Wolf 630 measured at 6.20 +/- 0.22 pc. (got this off SIMBAD)

Have these parallaxes been updated by GAIA or other data to make Wolf 629 and Wolf 630 part of the same star system?

And is Wolf 629 a binary star, per current literature?

6. Feel a bit foolish, just dug further into the CDS files, see attached. Thank you for your patience.

There really is a sextuplet star system just 21.2 light years away, made up solely of low-mass red dwarfs. The orbital elements must be stunning. The parallax discrepancies must have been resolved, then. Castor is not the closest sextuplet system!

Will this nearby system be searched for planets? One can only hope. That would be wild.

LATE ADD: Still think it odd that the only attempt to verify double-star status of Wolf 629 came up empty, but the label of spectroscopic binary still sticks. Why?
Last edited by Roger E. Moore; 2018-Oct-07 at 03:59 AM. Reason: late adds

7. Hmmm, most recent papers on this star system treat Wolf 629 / GJ 643 as a single star, as did Mazeh (2001), not as a spectroscopic binary, as does SIMBAD now.

Guess we're going back to quintuple status. Will keep looking at papers.

8. Oooooooo, I will use CDS more often for everything.

http://cdsportal.u-strasbg.fr/?target=GJ%20643

Link to GJ 643, one of the red dwarfs in this system. Wall to wall detail, bibliography, omg everything. I love CDS.

9. By request of the OP, moved from Q&A to Astronomy.

10. Originally Posted by Swift
By request of the OP, moved from Q&A to Astronomy.
Thank you!

11. Some side notes about this FIVE-star system, which still has a remote chance of being a sextuplet. For a brief period, it was thought this was a SEVEN-star system, and an example of this is the following paper.

LOW-ENERGY X-RAY OBSERVATIONS OF THE WOLF 630 SYSTEM

Hugh M. Johnson (Lockheed Missiles and Space Company) Received 1986 June 19; accepted 1986 October 22

The septuplet of M dwarfs is resolved into three components. Wolf 630ABab, Wolf 629ab, and VB 8AB, with the EXOSAT channel multiplier array (CMA). W630 and VB 8 have previously been observed with the Einstein high resolution imager (HRI) and W630 only with the Einstein imaging proportional counter (IPC) and solid state spectrometer (SSS). The ratio of CMA to HRI count rates for VB 8 can be produced with an isothermal plasma model temperature T = (6.4 +1.6/-0.9)E5 K, which is exceptionally low in the known range ofcoronal temperatures. The count rate during 18,112 s of effective exposure with EXOSAT shows that VB 8 flared once in 0.05-2 keV flux. T > 6.4E5 K in a flaring state, coupled with T < 6.4E5 K in a quiescent state during the HRI observation, may also represent the data for VB 8. The results are of special interest for objects near the limit of the hydrogen-burning main sequence.

12. Two of the red dwarfs in GJ 644/643 are being checked for exoplanets by two different long-term programs at the same time. The innermost members of the 5-star system, GJ 644 A/Ba/Bb, are so close to each other that there is little likelihood of exoplanets around them. GJ 643 and vB 8 (GJ 644 C) are well apart from the rest of the group. Cross your fingers. (GJ 643 was once suspected of being a spectroscopic double, and in the 1980s vB 8 (van Biesbroeck 8) was thought to be orbited by a brown dwarf.

https://arxiv.org/abs/1501.05012
A 3D Search for Companions to 12 Nearby M-Dwarfs
Davison, Cassy L, et al. (2015)

https://arxiv.org/abs/1711.06576
The CARMENES search for exoplanets around M dwarfs: High-resolution optical and near-infrared spectroscopy of 324 survey stars
A. Reiners, et al. (2018)