* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Home -> Astronomy News -> Stars/galaxy News -> DI Herculis
Post Info TOPIC: DI Herculis
Blobrana


L

Posts: 131433
Date:
RE: DI Herculis
Permalink  
 

Title: Analysis of Spin-Orbit Misalignment in Eclipsing Binary DI Herculis
Authors: Alexander A. Philippov, Roman R. Rafikov

Eclipsing binary DI Herculis (DI Her) is known to exhibit anomalously slow apsidal precession, below the rate predicted by the general relativity. Recent measurements of the Rossiter-McLauglin effect indicate that stellar spins in DI Her are almost orthogonal to the orbital angular momentum, which explains the anomalous precession in agreement with the earlier theoretical suggestion by Shakura. However, these measurements yield only the projections of the spin-orbit angles onto the sky plane, leaving the spin projection onto our line of sight unconstrained. Here we describe a method of determining the full three-dimensional spin orientation of the binary components relying on the use of the gravity darkening effect, which is significant for the rapidly rotating stars in DI Her. Gravity darkening gives rise to nonuniform brightness distribution over the stellar surface, the pattern of which depends on the stellar spin orientation. Using archival photometric data obtained during multiple eclipses spread over several decades we are able to constrain the unknown spin angles in DI Her with this method, finding that spin axes of both stars lie close to the plane of the sky. Our procedure fully accounts for the precession of stellar spins over the long time span of observations.

Read more (1481kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Oddball stars explained
New observations solve longstanding mystery of tipped rotation. In addition to shedding light on how binary stars form, the explanation knocks down a possible challenge to Einstein's theory of relativity

Read more

__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

August 17, 1985

Orbital motions are the classic testing grounds of theories of gravity. Precession of the orbit of the planet Mercury determined the superiority of Einsterin's theory over Newton's. Precession is a motion of the orbit as a whole: Not only does Mercury go around the orbit; at the same time the orbit itself swings around like the hand of a clock. In planets the latter motion is called precession of perihelion; in stars it is either precession of periastron or precession of apsides.
DI Herculis is an eccentric (highly elliptical) eclipsing system. Its orbit lies at such an angle that, viewed from earth, it has deep and narrow eclipses as one of the stars passes in front of the other. It is also fast, completing an orbit every 10.55 days. These characteristics make it favorable for such a test.
Read more

Position(2000): RA 18 53 26.2399, Dec +24 16 40.795

__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

DI Herculis is an 8th-magnitude eclipsing binary about 2,000 light years from earth. These two young blue stars are very close -- only one fifth the distance from earth to our sun. They orbit about a common center of gravity every 10.55 days.
The puzzle is that, as the two stars swing around one another, the axis of their orbit rotates or precesses too slowly. General relativity predicts a precession of 4.27°/century, but for DI Herculis the rate is only 1.05°/century. This does not sound like a figure large enough to get excited about, but it deeply troubles astronomers.

Read more

__________________
Page 1 of 1  sorted by
 
Quick Reply

Please log in to post quick replies.
Home -> Astronomy News -> Stars/galaxy News -> DI Herculis


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard