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Post Info TOPIC: Antares
Blobrana


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Alpha Scorpii
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Antares is visible in the sky all night around May 31 of each year, when the star is at opposition to the Sun.
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Blobrana


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RE: Antares
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Title: A hydrodynamic study of the circumstellar envelope of alpha Scorpii
Authors: K. Braun, R. Baade, D. Reimers, H.-J. Hagen

Context: Both the absolute mass-loss rates and the mechanisms that drive the mass loss of late-type supergiants are still not well known. Binaries such as alpha Sco provide the most detailed empirical information about the winds of these stars.
Aims: The goal was to improve the binary technique for the determination of the mass-loss rate of alpha Sco A by including a realistic density distribution and velocity field from hydrodynamic and plasma simulations.
Methods: We performed 3D hydrodynamic simulations of the circumstellar envelope of alpha Sco in combination with plasma simulations accounting for the heating, ionisation, and excitation of the wind by the radiation of alpha Sco B. These simulations served as the basis for an examination of circumstellar absorption lines in the spectrum of alpha Sco B as well as of emission lines from the Antares nebula.
Results: The present model of the extended envelope of alpha Sco reproduces some of the structures that were observed in the circumstellar absorption lines in the spectrum of alpha Sco B. Our theoretical density and velocity distributions of the outflow deviate considerably from a spherically expanding model, which was used in previous studies. This results in a higher mass-loss rate of (2 ± 0.5) x 10^-6 solar masses/yr. The hot H II region around the secondary star induces an additional acceleration of the wind at large distances from the primary, which is seen in absorption lines of Ti II and Cr II at -30 km/s.

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Blobrana


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On Sunday night, July 17/18, the waxing gibbous Moon, with 85 percent of its disk illuminated, will occult the red giant star Antares for observers in the western and southern USA, Mexico, Central America, the Caribbean Sea, and northern South America; observers along the coast of Vancouver Island, B.C., will have a graze, shortly before sunset. 

(Image Deleted)

This map shows the full region of visibility of this July 18th (UT) Antares occultation, and predictions of the total lunar occultation of Antares for many dozens of cities across North and Central America. 
During 2005, the Antares lunar occultation zones shift progressively south so this will be the last chance for most North American observes to see an occultation of this red giant star for a few years. 

The dark limb grazing occultation of Antares is visible near the northern limit line extending from Washington State to Texas and on to north-eastern North Carolina. 
The rest of the United States and Canada will be able to watch as the Moon slips just below Antares, without obscuring it.

Within an approximately mile-wide band generally just south of the predicted limit (the event occurs mainly in a low region of the Moon), you can see the bright red star disappear and reappear a few to several times among mountains and craters near the lunar north pole, with most of the events noticeably gradual, lasting even more than a second, due to the star's large angular diameter of about 0.03". Partial blinks might be seen as lunar mountain tops cover and uncover only part of the star, and similarly you might see the star reappear faintly only briefly in lunar valleys.


The Moon and Antares as they will appear from Los Angeles at 8:10 p.m. on July 17. Viewers in other locations will see a different setup.

Antares is ranked as the fifteenth brightest star in the sky, but you will likely need a small telescope or at the very least binoculars to follow the event due to the moons brightness. The fiery-red Antares has a 5th-magnitude companion star.

Previously, the Moon hid Antares on March 3 and May 24. After this event, the Moon will continue to cross paths with Antares on a monthly basis until February 2010. But many of these upcoming Antares occultations will favour localities south of the equator. Not until June 2009, will North Americans get another opportunity to watch the Moon hide Antares.

In the table below is a timetable for six selected locations, giving the local times and the Moon's altitude for both Antares' disappearance and reappearance. When a time is listed as p.m., it is for Sunday night, July 17. If a time is listed as a.m., it is for Monday morning, July 18. 
If the sky is clear with no significant haze, you should be able to see the Moon low in the south-southeast sky and be able to discern Antares with a small telescope. 

Location	Zone	Disappears	Altitude in degrees 	Reappears altitude 
Austin	        CDT	11:16 p.m.	32	11:47 p.m.	28
Los Angeles	PDT	8:14 p.m. 	26	9:09 p.m.	30
Miami	        EDT	12:46 a.m.	25	1:43 a.m.	16
New Orleans	CDT	11:35 p.m.	28	12:06 a.m.	24
Phoenix	         MST	8:32 p.m. 	29	9:16 p.m.	30
San Francisco	PDT	8:08 p.m. 	21	8:59 p.m. 	25


After closest approach, the Moon will move slowly away from Antares, with the Moon setting not long thereafter for eastern locations. Most of the United States and Canada will be in darkness, or twilight at the moment that Moon and Antares are closest together. 


Location	Zone	Closest approach	Separation 	Altitude 
Atlanta	       EDT	12:59 a.m.	0.01	18
Boston	       EDT	1:09 a.m.	0.03	5
Chicago	       CDT	11:44 p.m.	0.06	16
Denver	       MDT	10:07 p.m. 	0.05	24
Great Falls	MDT	9:54 p.m. 	0.06	16
Halifax	       ADT	2:09 a.m.	0.01	Moonset/0
Kansas City	CDT	11:29 p.m.	0.06	22
Montreal	EDT	12:59 a.m.	0.06	5
New York	EDT	1:06 a.m.	0.03	8
Salt Lake City	MDT	9:54 p.m. 	0.01	23
Seattle	        PDT	8:39 p.m. 	0.01	15
Vancouver	PDT	8:37 p.m. 	0.01	12
Washington,D.C. EST	1:04 a.m.	0.03	11
Winnipeg	CDT	11:19 p.m. 	0.11	13

In most cases, the distance separating Antares from the Moon's upper limb will be 0.05 degrees or less. To gauge just how small this is, consider that on the night of the occultation, the apparent width of the Moon will be equal to 0.54 degrees. So, as seen from Denver, the distance separating Antares from the Moon's rim will be equal to roughly 1/11 of the Moon's diameter. 
And for places where the separation is listed as 0.01 degrees, the miss distance will be equal to just 1/54 of the Moon's diameter. 



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Blobrana


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About an hour after sunset, the full moon will rise from the south-eastern horizon, followed by reddish star, Antares, in the constellation Scorpius.

At a distance of distance of 600 light years away, Antares, is a class M (M1.5) red supergiant with a colour similar to Mars. It is a relatively cool star only about 3600 degrees Kelvin at its surface. It is commonly mistaken for the red planet Mars, since it is found within the Zodiac; its name, Antares, or "Ant-Ares" means "like Mars". This magnificent first magnitude (typically 0.96) star is ranked the 13th brightest in the sky. It is a semi-regular variable that can change by around a magnitude over a period approaching 6 years. The star is huge with a radius of 3.8 AU, three-fourths the size of the orbit of Jupiter. It is so big that astronomers can detect and measure the size of its apparent disk.



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