COTM: Bootes

Ross Gould

Bootes, the ploughman, is one of the ancient constellations, recorded in early Greek times and likely pre-dating that period. Ptolemy in his Almagest (AD 150) assigns 23 stars to it. A large constellation of 907 square degrees, it streches from a little above the equator to above 50 deg. N in declination, near our horizon. The best months for Bootes in the earlier evening are June and July.

Bootes is easily found from its brightest star, the brilliant yellow Arcturus in the southern part of the constellation, its name given as "the Guardian of the Bear" by Burnham (Ursa Major is nearby to the North). Arcturus is the 4th brightest star in the sky (mv=-0.04), close behind Alpha Centauri (mv=-0.28). Like Alpha Cen. it has a large proper motion, first measured by Edmund Halley. TW Webb quotes Humboldt to the effect that Arcturus has moved 2.5 times the Moon's diameter since the days of Hipparchus. It is moving towards Virgo, and presently approaching the Sun at a slow rate, though now almost at minimum distance -- about 36 ly.

Bootes has many fine double stars, one globular cluster, and plentiful galaxies -- though most of them are faint. It lacks open clusters and nebulae, being distant from the Milky Way. My observations in what follows were, except wheere indicated, with the 7-inch (18cm) refractor at Canberra Observatory.

The second brightest star in Bootes is Epsilon (14h 45 00 +27 04). Epsilon Bootes consists of stars of mag. 2.5 and 4.9, at a sep. of 2.6" and PA of 343 deg. in 1988. A long period binary, there has been only a slow increase in PA since discovery. FGW Struve who discovered it in 1829 called it "Pulcherrima" in token of its beautiful effect. Epsilon is a very fine coloured double,m the spectral types K0 and A2. The colours are generally described as yellow-orange and bluish, though occasionally "B" is called green. Epsilon is not easy for small telescpes, and I found that the effect was much better at 189x than 100x.

The only globular in Bootes is NGC 5466 (14 05.5, +28 32), of modest size and rather loose - 11' diameter on photos, and mv=9.1. It was only a dim smudge, vaguely granular, at 100x and 180x. From our latitude it's too far north for best effect, and isn't bright anyway.

For those who want a globular in this part of the sky, M3 is 5 deg. W. (in Canes Venatici) at nearly the same declination. M3 is bright, fairly large and shows stars at 100x - much more satisfying.

Bootes contains a variety of binocular accessible star pairs. One is Delta Bootes (15h 15.5, +33 18), a cpm (common proper motion) pair - this one will show in a non- Telrad finder, mags 3.5 and 7.8 at some 105" apart. Both are spectral type G, with "A" the deeper yellow. Some other binocular pairs are Mu (see below); Iota (14h 16.2, +51 22) - mags 4.9 and 7.5 at 38.5"; S 656 (13h 50.3 + 21 15 - mags 6.9 and 7.4 at 86"; and Eta (13h 54.7, +18 24, mags 2.8 and 8.8 at 112".

Doubles and Galaxies

Further pairs, from a constellation with quite a few.

Mu (15h 24.5, +37 20) is a wide cpm pair, plus B is a binary - at 100x a bright yellow star has wide from it a fairly close moderately bright pair, deeper yellow. The pair is mags 7.2 and 7.8 at 2.1" in 1994. A fine effect, though like so m,any Bootes pairs it is in a field that adds nothing.

Xi (14h 51.4, + 19 06) is a beautiful uneven pair, yellowish and red - the mags are 4.7 and 7.0, presently about 6.5" separation with the companion NW. It is a binary of about 150 years period, now near maximum separation. A fine object which any small telescope should show.

Well north is 44 Boo ( 15h 03.8, +47 39), a binary in a very elongated apparent orbit, of 225 years - the companion is an eclipsing variable, with a period of only 6.4 hours. Magnitudes are 5.3 and (usually) 6.2. 44 Boo was discovered by FGW Struve in 1826, at 2.2" in PA231 deg. Following a minimum separation of only 0.4", the pair is widening again, towards a secondary maximum around 2005 - the 1992 measure was 1.8" in PA 049 deg. Viewed from California last year, 44 Boo with a C8 at 80x was a bright mid-yellow star in a field with some other fairly bright stars; at 200x it was a close slightly uneven pair. A good object when definition permits.

At a more helpful declination is 1 Boo (13h 40.7, +19 57). This pair was clear atr 100x - easy, and quite attractive - a bright star with noticeably less bright companion (mags 5.8 and 8.8.) The 1976 measure was 4.7" at PA136 deg. Hartung descibes the colours as pale yellow and reddish; but with 18cm I was not sure of the colour of "B".

Kui 66 (15 Boo) (14h 14.8, +10 06) is a test object - at mags 5.4 and 7.9 it is difficult at 1.0" largely because of the brightness difference. The PA in 1984 was 111 deg. The companion was not certainly visible at 330x in variable seeing. It is likely to be tough even with 25cm and needs steady air.

STF 1835 (14h 23.4, +08 26) mags 5.1 and 6.9. At the north end of a line of three bright stars, an easy eneven pair of contrasting yellow tones, at 6.2" separation. A fine object. The less bright star is a very close 40yr binary, usually beyond amateur telescopes (max separation of 0.3").

Pi (14h 40.7, +16 25) is another easy double. The mags 5.0 and 5.9 stars are nicely separated at 5.6", easy at 100x. A mag. 10 star is 2' S. Zeta (14h 41.1, +13 44). The stars, mags 4.4 and 4.8 are at a tight 0.85" in PA 300 deg. at present. The eccentricity of the orbit varies the separation from only 0.03" (about 2021) to 1.16"(in 1959). In the telescope, at 100x a bright white star dominates a field including one other bright star. 190x showd Zeta as a figure-8 shape at 330x it became a nest bright pair, nicely split.

STF 1884 (14h 48.4, +24 22), is a moderately close pair, mags 6.1 and 7.7 at 1.7" (PA 055 deg, 1957). There has been no certain change since Struve's time.

STF 1910 (15h 07.6, +09 13) is an even and easy mag. 7.5 pair, quite a good "snake eyes" double at 100x. The 1971 measure was 4.3" in PA 211 deg.

STF 288 (14h 43.4, +15 42) is a 215 year binary, measured in 1993 as 1.3" in PA 167 deg. The mags are 6.9 and 7.5. At 100x it was a closebut fairly bright deep yellow pair. 180x gave a better view, a rather nice slightly uneven double. Other good pairs such as 39 Boo and BX Boo are rather far north to be easily seen from Canberra.

And so to the galaxies. Many of the moderately bright galaxies are too far north for easy observing at our latitude, because they are 40 or 50 deg. north in declination. However among the more accessible is the only galaxy that Hartunglists for Bootes, NGC 5248 (13h 37.5, +08 53) - this 10th mag. spiral is 6.5'x5' on photos, and was a dim smudge of reasonable size with 18cm -0 though not bright, it showed hints of structure at 180x. More aperture would help greatly.

Some other galaxies to try, mostly in the southern part of Bootes, for those with reasonable aperture, would include NGC 5532 (14h 16.9, +10 48) is an S0 galaxy 2'x2' on photos, listed as mv=12.0.

NGC 5600 (14h 23.8, +14 38) type Sc 1.5'x1.5, mv=12.7.

NGC 5614 (14h 24.1, +34 52) type S, 2.5'x2.5', mv=11.7

NGC 5665 (14h 32.4, +08 05) type Sc, 2'x1.5', mp=12.8

NGC 5669 (14h 32.7, +09 53) type Sc, 5'x3', mp=12.25

NGC 5857 and NGC 5859 (15h 07.5, +19 36 and 15h 07.6, +19 35) types SBb (both), mv=13.1 and 12.4, 1.5'x1' and 3'x1'.

In the middle north of Bootes are NGC 5529 and NGC 5533 (14h 15.6, + 36 13 and 14h 16.1, + 35 21) types Sc and S, 6'x1' and 3'x2', mp about 12.6 for each, 5533 has mv= 11.8.

A final double star for those who like horizon hugging objects. Kappa Boo (14h 13.5, +51 47) is a fine pair from more northerly latitudes - mags 4.5 and 6.7 at 13.4". Because it's wide, it shouold be possible from Canberra despite (very) low alititude - from California, with the C8, Kappa Boo at 80x was a fine bright pair showing colour contrast, pale yellowish green and bluish purple. An excellent pair in a sparse field. Bootes is a neglected region for most observers in our time, due to the present unfashionableness of doulbe star observing. Yet it includes some fine objects if your telescope can give sharp star images rather than fuzzy blobs.