Cor Caroli 

Richard Harshaw
Star: Cor Caroli, Alpha CVn (STF 1692) 
Location of site: Northern Kansas City, Missouri (USA) 
94d 30m west longitude, 39d 15m north latitude 
980 ft above Mean Sea Level 
Date of observations (UT): UT: 02:15 of Sept. 16, 2000 
Site classification: suburban 
Sky conditions: 
seeing-- 4/10 up to 8/10, in short spans of time 
transparency-- 8 out of 10 
limiting visual magnitude-- 5.0 mag 
Telescope: Celestron C-8 
Eyepiece: 32mm  (65x). 
 
 		 At this time of year, Cor Caroli lies behind my neighbor's house.  The report I will show is from an earlier observation. 
 
Position:  1256+3819 
Magnitudes:  2.9, 5.5 
Sep/PA's:  19 = / 229 = 
Year of last measurement:  1991 
Distance (light years):  110 
Luminosity (in suns):  72 
Eyepiece and magnification:  32mm  (65x). 
Colors noted:  B, W.  Webb saw them as W or yW and L. 
 
This is one of the finest doubles in the sky! 
It is popularly believed to be named for King Charles, king of England, by Edmund Halley (because it supposedly shone with extra splendor on the night of May 29, 1660, the eve of Charles's return to England), but actually it was named for  the executed Charles I, the star's full name being COR CAROLI REGIS MARTYRIS. 
 
It is rich in silicon, europium and mercury, and is a member of the Hyades group.  It is 4.1 times larger than the Sun and is the prototype Alpha CVn variable.  It is also an infra-red source. 

First measure:  19.9" @ 227 (F. Struve, 1830). 
Rating:  1 

James Kaler's Star Notes (used with permission): 
Though this star is third magnitude, it is easy to find and is important all out of proportion to its brightness. Cor Caroli is the brightest star of the modern constellation Canes Venatici, the Hunting Dogs, invented in the 17th century by the astronomer Hevelius to help fill in the blanks left over by the ancients. If you look on the line perpendicular to the Big Dipper's handle just toward the south, you find a pair of stars extending parallel to the handle; the brighter is Cor Caroli, the Alpha star. 
 
In a telescope it is paired with a fainter fifth magnitude star of little interest, the fainter called Alpha-1, the brighter, really Cor Caroli itself, Alpha-2. It is a white star with a surface temperature of 9500 Kelvin, about double that of the Sun. Though almost 50 times more luminous than the Sun its distance of 97 light years renders it relatively faint compared with others of its class. 
 
Much more interestingly, Cor Caroli (Alpha-2) is a "magnetic star," and possesses one of the strongest known magnetic fields among otherwise normal "main sequence" stars, youthful unevolved stars like the Sun. The Sun has an overall magnetic field that is only a few time stronger than Earth's; Cor Caroli's, on the other hand, has one 1500 times stronger. The star also has a weird chemical composition in which elements such as silicon, mercury, and rarer elements such as europium are locally enormously enhanced. Astronomers think the magnetic field is responsible for helping to redistribute the elements in the star's atmosphere, apparently enriching some, depleting others. 
 
 
 
Ilario Melandri
Star: Cor Caroli, Alpha CVn (STF 1692) 
Date & Time: 22/09/2000 – 18.00 UT 
Seeing: 6 <1-10 Seeing Scale (10 best)>  
Location of site: Italy, Ravenna, San Romualdo, Lat 44 32’N Lon 12 08’E 
Elevation: 0 m 
Site classification: Rural  
Sky darkness: 1 <Limiting magnitude> 
Temperature: +21C 
Telescope: 150 mm f/15 achromatic refractor (lens by Romano Zen, Venice). 
Magnification: 140x (Plossl 16mm)		 The sep. of 19.4” at a distance of 65 light years, corresponds to 387 
Astronomical Units, something like 5 diameters of the Pluto’s orbit 
around the Sun. 
 
 
 
 
Jim Jones
Star: Cor Caroli, Alpha CVn (STF 1692) 
Date & Time: 0346 UTC Sept 22, 2000 
Seeing: 6 <1-10 Seeing Scale (10 best)> 
Location of site: Lake Oswego, Oregon, USA  
Site classification: Suburban 
Sky darkness: 5 <Limiting magnitude>  
Telescope: 8 inch LX50 SCT 
Eye Piece(s): 42 mm Ultima
Magnification: 47x
 
 		 Arrived just before dusk.  Venus was setting fast and I tried to get the telescope set up for a peek.  No such luck.  It set just as I got my act together.  So I waited a bit and grabbed Cor Caroli while I could.

Primary...blue
Companion....yellow-orange
Est PA without instrumentation....245d 

 
 
 
 
Patrick J. Anway 
Star: Cor Caroli, Alpha CVn (STF 1692) 
Date & Time: Sept. 27, 2000; 8:30pm EDT (03:00 UT) 
Seeing: 7 <1-10 Seeing Scale (10 best)> 
Location of Site: Pictured Rocks,  Michigan USA 
Site Classification: Rural 
Sky darkness: 6.0+ <limiting magnitude> 
Sky condition: no clouds, no moon 
Temperature: 42deg F (5deg C) 
Telescope: Unitron 75mm f/16 
Eyepieces: 10mm, 12.5mm orthos 

 
 

 Though I had observed Cor Caroli many times in the past, I was determined 
to observe it again as an Olympiad. However, given the time of year, I knew 
that it would be impossible from my observatory; it would take a low 
western horizon and twilight. I knew just the place!  Starting in Munising 
bay and extending some thirty miles east along Lake Superior is "Pictured 
Rocks", a series of rock cliffs rising from the lake to a height of 
150' to 300' 
 
From this standpoint, I would have a chance. I took up position a few miles from town on the east side of the bay looking west and waited. Arcturus, Deneb, Vega and Altair signaled the approach of twilight. There were whitecaps on the bay, some 165 feet below and with nothing between me and Canada nearly 287 miles to the north, I could feel the north wind biting at my ears and cheeks. Next came Alkaid, Mizar and 
Alioth and I knew Cor Caroli would soon follow. There it was, about 25 degrees above the horizon. Under the right circumstances, an easy prey. 
 
Observation/Notes: Using the 10mm for 120X the pair separated into a yellow-white primary and a pink-blue secondary. What a striking couple - even in the low altitude, which no doubt affected their glory. Flammarion gives "yellow of gold & lilac" and calls the pair "Superb". He refers to Alpha CVn as "Le Coeur de Charles", "The Heart of Charles" and attributes the name to Halley. 
 
Olcott gives both components yellow and says this: "7 degrees north-northwest of Cor Caroli is "La Superba", a 5th magnitude star of brilliant red color. It is one of seven or eight naked eye stars of 4th spectral class and is noted for the brilliant coloring of it's flashing rays." Couteau called it "one of the prettiest doubles in the sky" and suggests to" look at it with a small telescope." It was an easy observation with a 3" 
 
 
 
Pino Bandini
Star: Cor Caroli, Alpha CVn (STF 1692) 
Location of site: Ravenna, Italy 
Date of observations (UT): 30/09/2000 
21.47 UT 
Site classification: Urban 
Sky conditions: 
Seeing: 7 (10 best) 
Temperature: +21C 
Limiting visual magnitude: -- 
Telescope: Celestron 8 
Magnification: 200x (Plossl 10mm) 
 
 		 Note: color white of both components