* Astronomy

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


L

Posts: 131433
Date:
RE: Alcor
Permalink  
 

An astronomer at the University of Rochester and his colleagues have made the surprise discovery that Alcor is also actually two stars, and is apparently gravitationally bound to the Mizar system, making the whole group a sextuplet. This would make the Mizar-Alcor sextuplet the 2nd nearest such system known. The discovery is especially surprising because Alcor is one of the most studied stars in the sky.
Read more

__________________
Blobrana


L

Posts: 131433
Date:
Alcor B
Permalink  
 

One of the stars that makes the bend in the ladle's handle, Alcor, has a smaller red dwarf companion, new observations have revealed.
Alcor is a relatively young star twice the mass of the Sun. Stars this massive are relatively rare (less than a few percent of all stars), short-lived, and bright.
Read more

ALe1.gif
Credit: University of Rochester

This image shows Alcor and the newly discovered Alcor B, as imaged by scientists at the University of Rochester.

__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

The Big Dipper still has a few secrets, astronomers reported Wednesday, despite its status as the night's best-known constellation.
In a study in the Astrophysical Journal, a team led by Ben Oppenheimer of the American Museum of Natural History in New York, reports that Alcor, the star at the bend in the "handle" of the Big Dipper, has a newly discovered co-star, dubbed Alcor b.
Read more

__________________
Blobrana


L

Posts: 131433
Date:
Mizar
Permalink  
 

Alcor
Observation data
Epoch J2000.0 Equinox J2000.0
Constellation Ursa Major
Right ascension 13h 25m 13.5s
Declination +54° 59' 17"
Apparent magnitude (V) +3.99
Absolute magnitude (V) +2.01
Distance 81.2 ± 1.2 ly
(24.9 ± 0.4 pc)
Spectral type A5V
Mizar  is a star in the constellation Ursa Major and is the second star from the end of the Big Dipper's handle. Its apparent magnitude is 2.23 and its spectral class is A1V. Mizar's name comes from the Arabic mzar, meaning a waistband or girdle.

With normal eyesight one can make out a faint companion just to the east, named Alcor or 80 Ursae Majoris. Alcor is of magnitude 3.99 and spectral class A5 V. Mizar and Alcor together are sometimes called the "Horse and Rider," and the ability to resolve the two stars with the naked eye is often quoted as a test of eyesight, although even people with quite poor eyesight can see the two stars.

Source

__________________
Blobrana


L

Posts: 131433
Date:
Alcor
Permalink  
 

Title: Discovery of a Faint Companion to Alcor Using MMT/AO 5 \mu m Imaging
Authors: Eric E. Mamajek (1), Matthew A. Kenworthy (2), Philip M. Hinz (2), Michael R. Meyer (2,3) ((1) University of Rochester, (2) Steward Observatory, University of Arizona, (3) Institute for Astronomy, ETH Zurich)

We report the detection of a faint stellar companion to the famous nearby A5V star Alcor (80 UMa). The companion has M-band (\lambda = 4.8 \mu m) magnitude 8.8 and projected separation 1".11 (28 AU) from Alcor. The companion is most likely a low-mass (~0.3 \msun) active star which is responsible for Alcor's X-ray emission detected by ROSAT (L_{X} \simeq 10^{28.3} erg/s). Alcor is a nuclear member of the Ursa Major star cluster (UMa; d \simeq 25 pc, age \simeq 0.5 Gyr), and has been occasionally mentioned as a possible distant (709") companion of the stellar quadruple Mizar (\zeta UMa). Comparing the revised Hipparcos proper motion for Alcor with the mean motion for other UMa nuclear members shows that Alcor has a peculiar velocity of 1.1 km/s, which is comparable to the predicted velocity amplitude induced by the newly-discovered companion (~1 km/s). Using a precise dynamical parallax for Mizar and the revised Hipparcos parallax for Alcor, we find that Mizar and Alcor are physically separated by 0.36 ±0.19 pc (74 ±39 kAU; minimum 18 kAU), and their velocity vectors are marginally consistent (\chi^2 probability 6%). Given their close proximity and concordant motions we suggest that the Mizar quadruple and the Alcor binary be together considered the 2nd closest stellar sextuplet. The addition of Mizar-Alcor to the census of stellar multiples with six or more components effectively doubles the local density of such systems within the local volume (d $<$ 40 pc).

Read more (50kb, PDF)

__________________
Page 1 of 1  sorted by
Quick Reply

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


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard