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BURNHAM'S CELESTIAL HANDBOOK: An Observer's Guide to the Universe Beyond the Solar System
By ROBERT BURNHAM JR. Dover Publications, Inc.
Copyright © 1978 Robert Burnham, Jr.
All rights reserved.
ISBN: 978-0-486-31793-9
CHAPTER 1
CHAMAELEON
LIST OF DOUBLE AND MULTIPLE STARS
CIRCINUS
LIST OF DOUBLE AND MULTIPLE STARS
DESCRIPTIVE NOTES
BLDΑBLD Mag 3.18; spectrum F0 Vp; position 14384s 6446. Alpha Circini is approximately 65 light years distant and has an actual luminosity of about 17 suns (absolute magnitude +1.7). The annual proper motion is 0.31" in PA 217º; the radial velocity is about 4 miles per second in recession.
The 9th magnitude companion at 15.7" is a K5 star, sharing the proper motion of the primary, and maintaining the same separation since the first measurements were made in 1837. The PA is decreasing slowly, from 244º to 232º between 1837 and 1951. Projected separation = 320 AU.
COLUMBA
LIST OF DOUBLE AND MULTIPLE STARS
DESCRIPTIVE NOTES
BLDΑBLD Name- PHACT or PHAET. Mag 2.64; spectrum B8 Ve. Position 05378s3406. The computed distance is about 140 light years; the actual luminosity about 145 times that of the Sun (absolute magnitude -0.6). The star has an annual proper motion of 0.025"; the radial velocity is 21 miles per second in recession.
The 11th magnitude companion at 13.5" is evidently not physically connected with the primary; the separation is increasing slowly from 11.6" in 1900.
BLDΒBLD Name- WEZN. Mag 3.12; spectrum K1 III. The position is 05492s3547. The distance of this star is approximately the same as Alpha Columbae, about 140 light years. The computed luminosity is then about 90 times that of the Sun (absolute magnitude 0.0). The annual proper motion is 0.40" in PA 7º; the radial velocity is 54 miles per second in recession.
BLDΜBLD Mag 5.16; spectrum 09.5 V; sometimes given as B0. Position 05441s3219. Mu Columbae is a famous "Runaway Star", one of three known early type stars which appear to be moving out at high speeds from the nebulous region of Orion. All three stars seem to be at about the same distance as the Orion Association, and have apparently been ejected from that region during the last few million years, possibly by some process connected with the explosion of supernovae. The other two stars are 53 Arietis and AE Aurigae, both identified by abnormally high space velocities. AE Aurigae is the most interesting of the three; its rapid passage through the heavens is presently carrying it through the large diffuse nebulosity IC 405, and the structure of the nebulosity is evidently being greatly altered by the star's intense radiation. Mu Columbae itself has an annual proper motion of about 0.025" in a direction slightly east of due south; the true space velocity is about 74 miles per second.
For a diagram of the plotted paths of all three stars refer to AE Aurigae (page 288).
COMA BERENICES
LIST OF DOUBLE AND MULTIPLE STARS
LIST OF VARIABLE STARS
[TABLE OMITTED]
LIST OF STAR CLUSTERS, NEBULAE, AND GALAXIES
DESCRIPTIVE NOTES
BLDΑBLD (42 Comae) Mag 4.23; spectrum F5 V. Position 13076n1748. Double star, discovered by F.G. W.Struve in 1827. This is a close and rather difficult binary system, but of special interest from the rare circumstance that the orbit is seen almost exactly edge-on; the two stars thus appear to move back and forth in virtually a straight line, with a nearly constant PA. The period is 25.85 years, with the apparent separation varying from practically zero to a maximum of about 0.9". The semimajor axis of the orbit is 0.67"; the eccentricity is 0.5. Owing to the orientation of the orbit with respect to the Solar System, the time of apparent closest approach (1949) does not coincide with true periastron passage (1963).
Although T.W.Webb speaks of the two stars as "making an occultation about every 13 years" there is no real evidence that either star actually eclipses the other. From computations by H.Haffner (1948) and F. Pavel (1949) it now appears that the orbit is inclined just one-tenth of a degree from the edge-on position, implying that no real eclipse can occur. The two stars are nearly identical in size, type, and brightness; the magnitudes are both 5.1 and both spectra are F5 V. Each star is about 3 times as 'luminous as the Sun, and the mean separation of the pair is close to 10 AU, about the separation of Saturn and the Sun.
The distance of the system is approximately 65 light years, the annual proper motion is 0.45" in PA 287º, and the radial velocity is 10½ miles per second in approach.
THE COMA STAR CLUSTER One of the best known galactic star clusters, the Coma Berenices Star Cluster is a conspicuous scattered group of naked-eye stars, centered about midway between Alpha Canum and Beta Leonis, near 12220n2600. The cluster is not listed in the NGC or in Messier's catalog, but is sometimes referred to by its number in the catalog list of Melotte - "Mel 111". Covering an area about 5º in diameter, the cluster contains, as its brightest members, the fifth magnitude stars 12, 13, 14, 16, and 21 Comae. About thirty fainter stars have been identified as probable members, and a few others may await discovery. The bright stars 15, 18, and 7 Comae do not appear to be physical members of the group, but the star 31 Comae, some 5º from the cluster center, is probably a member. The information in the table below has been compiled from the Yale "Catalogue of bright Stars" (1964).
As a cluster, the Coma group is at its best in a pair of good binoculars, but is completely lost in the much narrower field of the telescope, which can show only a small portion at any one moment. G.P.Serviss spoke of noting a "curious twinkling, as if gossamers spangled with dewdrops were entangled there. One might think the old woman of the nursery rhyme who went to sweep the cobwebs out of the sky had skipped this corner, or else that its delicate beauty had preserved it even from her housewifely instinct.." T.W.Webb remarked that such a group obviously requires only distance to become a nebula to the naked eye.
The cluster is named in honor of Berenice II of Egypt, who was the Queen of Ptolemy III (246 - 221 BC). In one of the most appealing star legends we are told of the Queen's vow to sacrifice her famed "amber tresses" in the temple of Aphrodite at Zephyrium, following the king's safe return from battle. After the offering mysteriously vanished from the temple, the court astronomer Conon convinced the royal couple that the lost tresses had been transformed by the ¡gods into a constellation, and enshrined forever among the stars. The Roman poet Catullus (about 60 BC) refers to this legend when he speaks of
"the consecrated offering of Berenice's golden hair, which the divine Venus placed, a new constellation among the ancient ones, preceding the slow Bootes, who sinks late and reluctantly into the deep ocean ..."
In the coins of Berenice, we find some of the most exquisite coin portraits which have come down to us from the ancient world, particularly in the large gold octadrachms and decadrachms dating from the early days of the reign of Ptolemy III. "During this reign..... Egypt had command of the sea", states Professor Barclay V.Head in his monumental work Historia Numorum (1911) "and her empire embraced many of the maritime districts of Asia Minor, even extending across the Aegean into Thrace. Hence the appearance of Egyptian influence at mints like Ephesus and Ptolemais-Lebedus. In the absence of specific local and other marks, the Ptolemaic coins issued in these regions can seldom be attributed with certainty, ..." Prof. Head suggested, however, that the much- admired gold octadrachm of Berenice was probably minted at Ephesus on the west coast of Asia Minor, famous as the site of the great Temple of Diana, one of the ancient Seven Wonders. The respected German authority K.Regling dated this same coin, on the basis of a study of die-styles, to 258 BC, the year of the marriage of the young Berenice of Cyrene to the future Ptolemy III. The ancient city of Berenice, named for the queen, is still in existence as the modern Benghazi in Libya, capital and chief port of the province of Cyrenaica.
Before the days of Berenice, however, the star group seems to have been regarded as a part of the constellation Leo, marking the tuft of hair at the end of the Lion's tail. The Arabian names, Al Halbah and Al Dafirah refer to this identification and have been translated "the Coarse Hair" or "The Tuft". Eratosthenes, however, in the 3rd Century BC, refers to the group as "Ariadne's Hair" though in another passage he does connect it with the Egyptian Berenice. In various star maps of the late Middle Ages the cluster is identified as a rose-wreath or ivy-wreath, and occasionally as a Sheaf of Wheat held in the hands of Ceres or Virgo. These identifications seem to date back to a time when Coma was considered a part of the constellation Virgo. According to R.H.Allen, the astronomer Tycho Brahe "set the question at rest in 1602 by cataloguing it separately, adopting the early title as we have it now."
At a distance of about 250 light years, the Coma group is one of the nearest of all the star clusters; probably only the Ursa Major Group and the Hyades in Taurus are closer. Cluster members may be identified by the annual proper motion of the group, about 0.02" in P.A. 218º, and by the fact that the radial velocity of the members averages nearly zero. Any star with a high radial velocity is thus immediately disqualified. In one of the first really comprehensive studies of the group, R.J.Trumpler (1938) identified 37 stars as true cluster members on the basis of both proper motion data and radial velocity measurements. The most luminous members, as 14 and 16 Comae, have about 50 times the luminosity of the Sun. The faintest stars accepted as members are about 1/3 the brightness of the Sun. Spectral types range from A3 to about G9. As a standard of comparison, our Sun at the distance of the Coma Cluster would appear as a star of magnitude 9.2.
There are eight known spectroscopic binary stars in the Coma Cluster, with orbital elements presently available for several of the brighter ones. The bright star 12 Comae is the most interesting of these. It is a spectroscopic binary with a period of 396.49 days, but there is also a distant visual companion of the 8th magnitude at 66" in PA 167º, almost certainly a true cluster member. The spectrum of 12 Comae is composite, GO III + A3 V; the spectrum of the visual companion is about F8. In addition, about 0.5º to the southeast is the binary Σ1639, with a computed period of some 600 years and a semi-major axis of about 1". The orbit has an eccentricity of about 0.9 and the spectrum of the brighter star is about F0.
The Coma Cluster contains no giant stars, though the H-R Diagram (below) shows that the brightest members are just beginning to evolve toward the giant stage. The total mass of the group is probably under 100 solar masses. One of the peculiar features of the cluster is the apparent lack of fainter stars; the main sequence seems to terminate abruptly at apparent magnitude 10½, which corresponds to an absolute magnitude of about 6. Fainter and redder dwarf stars, actually the commonest stellar types, seem to be missing completely in the Coma group. If we compare this cluster with the famous Pleiades, it seems relatively poor in stars and only about a quarter as thickly populated, although the volumes of the two clusters are nearly equal. The sparseness of the Coma group suggests the possibility that the cluster may be gradually dispersing due to the small total mass. The computed star density is about one star per 10 cubic parsecs, a value very near the theoretical lower limit for stable clusters. In terms of age, the Coma group appears to be older than the Pleiades, but younger than Praesepe (M44) in Cancer or the Hyades Cluster in Taurus. (For a discussion of cluster age-dating, refer to M13 in Hercules)
M53 (NGC 5024) Position 13105n1826. A rich globular star cluster which forms a pair of 1º separation with the more unusual cluster NGC 5053. M53 itself lies 1º northeast of the binary Alpha Comae, and was first observed by J.E.Bode in February 1775. He referred to it as "a new nebula, appearing through the telescope as round and pretty lively"; the use of the last term suggests some hint of resolution. Messier's independent discovery occurred just two years later, in February of 1777; he found it "round and conspicuous" but "without stars" and compared it afterwards with the comet of 1779. Bright and well condensed, the cluster is an easy object for the small telescope, appearing as a round nebulous spot in a three-inch glass, but resolving into a wonderful swarm of tiny star images with larger instruments. Partial resolution usually requires a 6-inch telescope. In the greatest telescopes M53 is more than worthy of Webb's description: "a brilliant mass of minute stars, blazing in the center." John Herschel spoke of the radiating curves and streams of stars which adorn the outer edges, an appearance which is seen in many other bright globulars as well. Sir William Herschel, with his great reflector, spoke of M53 as "one of J the most beautiful sights I remember to have seen in the heavens. The cluster appears under the form of a solid ball consisting of small stars quite compressed into a blaze of light with a great number of loose ones surrounding it and distinctly visible in the general mass. Similar in appearance to M10". Admiral Smyth saw M53 as "a mass of minute stars 11-15 mag. and from thence to gleams of star-dust, with stragglers.... and pretty diffuse edges.." K.G.Jones (1968) rates it as "certainly one of the most beautiful" of the globulars. "It consists of a brilliant nucleus about 2' in diameter, surrounded by a dusky halo of light that gives it a glittering gem- like appearance. The background is dark but glimpses of numerous, faint stars can be obtained in clear conditions."
The total photographic magnitude of M53 is about 8.7, the extreme diameter about 14', and the integrated spectral type is F4. The cluster lies at a distance of about 65,000 light years; the resulting total luminosity is about 200 thousand times the Sun. Radial velocity studies show an approach velocity of about 70 miles per second. Some 45 variable stars are known in M53.
One degree to the southeast is the peculiar cluster NGC 5053, an unusual object which from its appearance could be classified as either a very loose globular or a very rich galactic cluster. It was discovered by Sir William Herschel in 1784, and may be detected in an 8-inch glass as a faint hazy spot of about magnitude 10½. It contains no dense nucleus of stars, and the faint members are widely separated even at the cluster center. Resolution can be achieved only with rather large telescopes.
The classification of this system as a globular is supported by the color-magnitude diagram and the presence of short-period pulsating variables of the RR Lyrae type. The population is about 3400 stars down to the 21st magnitude, decidedly sparse for a globular cluster. With an actual diameter of close to 100 light years, the resulting density is evidently not much more than 0.3 star per cubic parsec. The distance of the cluster seems to be comparable to that of M53; in fact the studies of the variables in the two groups suggest that NGC 5053 is probably slightly nearer to us than its brighter neighbor. The best present figure is about 55,000 light years, which gives the cluster a total luminosity of some 16,000 suns. This is one of the lowest luminosities derived for any globular cluster; the great Omega Centauri, for comparison, shines with nearly the light of a million suns. (Refer also to NGC 5139 in Centaurus and M13 in Hercules)
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Excerpted from BURNHAM'S CELESTIAL HANDBOOK: An Observer's Guide to the Universe Beyond the Solar System by ROBERT BURNHAM JR.. Copyright © 1978 Robert Burnham, Jr.. Excerpted by permission of Dover Publications, Inc..
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