<p>The quoted passage says explicitly only that the stars observed velocity amplitude changes over time (due to precession); that does not imply that precession itself changes, but merely that we can actually observe its effects in terms of seeing different radial velocity amplitude (<span class="math-container">$V_{rot}\sin i$</span>).</p>
<p>DI Herculis is assumed to undergo <a href="https://en.wikipedia.org/wiki/Apsidal_precession" rel="nofollow noreferrer">apsidal precession</a>, thus the orientation of the ellipse relative to our line of sight (LOS) changes over time. We observe the radial velocity projected onto our LOS - thus <span class="math-container">$v_{orbit}\sin i$</span>. Consider these cases <span class="math-container">$v_1$</span> and <span class="math-container">$v_2$</span> in the following graphics, observer on the right:
<a href="https://i.sstatic.net/z2Rfj.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/z2Rfj.png" alt="Effect of absidal precession on observed radial velocity" /></a></p>
<p>In case 1 (the vertical ellipse), the orbital velocity of the observed star is quite different (much smaller) when it is moving away from us and much larger when moving towards us. This contrasts with the case where the semi-major axis of the orbit is aligned with our LOS: the minimum und maximum values for the velocity are equal.</p>
<p>Precession causes the orientation of this ellipse to change over time - and that and its influence on the observed orbital velocities is what the authors hint at.</p>

CC BY-SA 4.0
2022-04-24T21:58:05.477Z
just fyi the OP has just [shared a lot more information](https://astronomy.stackexchange.com/questions/49144/what-is-being-said-here-about-the-strange-precession-of-di-herculis?noredirect=1#comment108091_49144) in a comment. These articles explain a lot more
uhoh
CC BY-SA 4.0
2022-05-04T11:30:06.010Z
Wave analysis shows, DI Herculis’ has a synchronized gravitational and electromagnetic field which produces a min. (0.992 deg. / century) and a max. (1.46 deg. /century) precession.  V541 Cygni’s also produces a min. (0.603 deg. /century) and a max. (0.881 deg./ century) precession.  These double precession systems are unique because both precessions are observed but one is considered a better measurement.   An unchanged precession means these systems operate at min or max.

https://indjst.org/articles/binary-precession-solutions-based-on-synchronized-field-couplings

Thanks Planetmaker
Jamahl Peavey
CC BY-SA 4.0
2022-04-19T17:49:36.510Z
2022-04-19T17:49:36.510Z
planetmaker
<p>The binary star system DI Herculis was brought to the astronomy community by Edward Guinan because it has an observed precession which is far lower than the one predicted by General Relativity.  In 2009, a research team &quot;Solved the Problem&quot; by pointing to DI Herculis misaligned spin and orbital axis.  Zimmerman, Guinan, &amp; Maloney (2010) later replied with <a href="https://ui.adsabs.harvard.edu/abs/2010AAS...21541934Z/abstract" rel="nofollow noreferrer">The Eclipsing Binary Di Herculis: One Mystery Solved, But Another Takes Its Place</a><sup>1</sup></p>
<p>They state:</p>
<blockquote>
<p>Further, we find evidence that the projected rotation axes of the stars may be precessing, since it appears that the value of V(rot)sini has increased over the past 30 years</p>
</blockquote>
<p>Are they saying DI Herculis precession is changing?</p>
<hr />
<p><sup>1</sup>American Astronomical Society, AAS Meeting #215, id.419.34; Bulletin of the American Astronomical Society, Vol. 42, p.282</p>

CC BY-SA 4.0
2022-04-19T00:22:24.793Z
Interesting question, *Welcome to Astronomy SE!* It looks like there are three authors on that abstract so I've added the block-quote format and mentioned all three. If this is inaccurate feel free to edit further.
uhoh
CC BY-SA 4.0
2022-04-19T14:09:12.083Z
Thanks for the warm welcome and detailing content for the question.
Jamahl Peavey
CC BY-SA 4.0
2022-04-23T13:20:47.917Z
I am team leader for a mechanical engineering group which is developing new tools for understanding how fields interact based on my published research.  Are any other astronomers certain this is the correct answer or would I need to wait to accumulate enough reputation for a bounty?  Thanks for everyones help.
Jamahl Peavey
CC BY-SA 4.0
2022-04-23T15:28:49.997Z
I'm happy to add a bounty to the question (I'm a very active "bountier") but there's no guarantee it will have any effect. In this case there might not be a single *right answer* since what you've quoted is only a short abstract, not a complete scientific paper. There's no data shown, no analysis described in detail. This abstract seems to be a "teaser" for a talk at a conference, just enough to make people interested in going to the talk. If you want to look into [Apsidal](https://en.wikipedia.org/wiki/Apsidal_precession) or [Nodal](https://en.wikipedia.org/wiki/Nodal_precession) precession
uhoh
CC BY-SA 4.0
2022-04-23T15:33:49.593Z
of stars, then perhaps asking new question not based on a 12 year old abstract would be better. Perhaps as simple as "What can make a binary star system's orbit precess? (nodal and/or apsidal)" On the other hand if this particular case is really interesting to you, then asking a new question about what all is known about this system and what work has been done on this system in the following 12 years after this abstract was published. Perhaps "What is currently known and thought about the dynamics of DI Herculis' orbit?" The current answer here is only interpreting this old abstract's wording.
uhoh
CC BY-SA 4.0
2022-04-24T16:05:32.860Z
This is the original article which is being assessed.
https://arxiv.org/pdf/0909.2861.pdf

It was revisited as early as last month.
https://iopscience.iop.org/article/10.3847/1538-4357/ac4f65/pdf

How the DI Herculis question is answered is no less critical to science than how the Mercury precession question was answered.  Thanks so very much for any support (Uhoh) and the Astronomy Stack Community.
Jamahl Peavey
CC BY-SA 4.0
2022-04-24T21:55:58.543Z
those should have been included in your original question
uhoh
CC BY-SA 4.0
2022-04-25T08:20:09.267Z
In retrospect, you are right.  Thanks for including info on the answer (uhoh).
Jamahl Peavey
<observational-astronomy><precession>
What is being said here about the strange precession of DI Herculis?
Jamahl Peavey
# What is being said here about the strange precession of DI Herculis?

(Asked by: username_0 on 2022-04-18)

The binary star system DI Herculis was brought to the astronomy community by Edward Guinan because it has an observed precession which is far lower than the one predicted by General Relativity. In 2009, a research team "Solved the Problem" by pointing to DI Herculis misaligned spin and orbital axis. Zimmerman, Guinan, & Maloney (2010) later replied with [The Eclipsing Binary Di Herculis: One Mystery Solved, But Another Takes Its Place](https://ui.adsabs.harvard.edu/abs/2010AAS...21541934Z/abstract)1

They state:

> Further, we find evidence that the projected rotation axes of the stars may be precessing, since it appears that the value of V(rot)sini has increased over the past 30 years

Are they saying DI Herculis precession is changing?

---

1American Astronomical Society, AAS Meeting #215, id.419.34; Bulletin of the American Astronomical Society, Vol. 42, p.282

**Tags:** observational-astronomy, precession

> **Comments:**
> **username_1**: Interesting question, *Welcome to Astronomy SE!* It looks like there are three authors on that abstract so I've added the block-quote format and mentioned all three. If this is inaccurate feel free to edit further.  
> **username_0**: Thanks for the warm welcome and detailing content for the question.  
> **username_0**: I am team leader for a mechanical engineering group which is developing new tools for understanding how fields interact based on my published research.  Are any other astronomers certain this is the correct answer or would I need to wait to accumulate enough reputation for a bounty?  Thanks for everyones help.  
> **username_1**: I'm happy to add a bounty to the question (I'm a very active "bountier") but there's no guarantee it will have any effect. In this case there might not be a single *right answer* since what you've quoted is only a short abstract, not a complete scientific paper. There's no data shown, no analysis described in detail. This abstract seems to be a "teaser" for a talk at a conference, just enough to make people interested in going to the talk. If you want to look into [Apsidal](https://en.wikipedia.org/wiki/Apsidal_precession) or [Nodal](https://en.wikipedia.org/wiki/Nodal_precession) precession  
> **username_1**: of stars, then perhaps asking new question not based on a 12 year old abstract would be better. Perhaps as simple as "What can make a binary star system's orbit precess? (nodal and/or apsidal)" On the other hand if this particular case is really interesting to you, then asking a new question about what all is known about this system and what work has been done on this system in the following 12 years after this abstract was published. Perhaps "What is currently known and thought about the dynamics of DI Herculis' orbit?" The current answer here is only interpreting this old abstract's wording.  
> **username_0**: This is the original article which is being assessed. https://arxiv.org/pdf/0909.2861.pdf  It was revisited as early as last month. https://iopscience.iop.org/article/10.3847/1538-4357/ac4f65/pdf  How the DI Herculis question is answered is no less critical to science than how the Mercury precession question was answered.  Thanks so very much for any support (username_1) and the Astronomy Stack Community.  
> **username_1**: those should have been included in your original question  
> **username_0**: In retrospect, you are right.  Thanks for including info on the answer (username_1).  

---

## 1 answers

### Answer by username_2 on 2022-04-19. Score: 3 | Accepted answer

The quoted passage says explicitly only that the stars observed velocity amplitude changes over time (due to precession); that does not imply that precession itself changes, but merely that we can actually observe its effects in terms of seeing different radial velocity amplitude ($V\_{rot}\sin i$).

DI Herculis is assumed to undergo [apsidal precession](https://en.wikipedia.org/wiki/Apsidal_precession), thus the orientation of the ellipse relative to our line of sight (LOS) changes over time. We observe the radial velocity projected onto our LOS - thus $v\_{orbit}\sin i$. Consider these cases $v\_1$ and $v\_2$ in the following graphics, observer on the right:
[![Effect of absidal precession on observed radial velocity](https://i.sstatic.net/z2Rfj.png)](https://i.sstatic.net/z2Rfj.png)

In case 1 (the vertical ellipse), the orbital velocity of the observed star is quite different (much smaller) when it is moving away from us and much larger when moving towards us. This contrasts with the case where the semi-major axis of the orbit is aligned with our LOS: the minimum und maximum values for the velocity are equal.

Precession causes the orientation of this ellipse to change over time - and that and its influence on the observed orbital velocities is what the authors hint at.

> **Comments:**
> **username_1**: just fyi the OP has just [shared a lot more information](https://astronomy.stackexchange.com/questions/49144/what-is-being-said-here-about-the-strange-precession-of-di-herculis?noredirect=1#comment108091_49144) in a comment. These articles explain a lot more  
> **username_0**: Wave analysis shows, DI Herculis’ has a synchronized gravitational and electromagnetic field which produces a min. (0.992 deg. / century) and a max. (1.46 deg. /century) precession.  V541 Cygni’s also produces a min. (0.603 deg. /century) and a max. (0.881 deg./ century) precession.  These double precession systems are unique because both precessions are observed but one is considered a better measurement.   An unchanged precession means these systems operate at min or max.  https://indjst.org/articles/binary-precession-solutions-based-on-synchronized-field-couplings  Thanks username_2  

---

