SELECTED SOUTHERN DOUBLES and VARIABLES
R.A. 19 Hours

γ CrA/ HJ 5084 / Gamma CrA (19064-3704) is a well observed binary star with the retrograde period of some 122 years. Listed as near equal 4.9v and 5.0v magnitude (4.53V & 6.42V?), and presently at PA 55° and 1.3 arcsec, making γ CrA visible in 10.5cm, though a number have reported this in 7.5cm - but I have never found it that easy.

Placed in the Southern Crown that was discovered by John Herschel from South Africa as HJ 5084. This binary is located at -37°S declination, γ CrA is more readily observed from the southern part of the United States than from more northern latitudes.

The orbital period found by W. Heintz in 1965 as 120.42 years, nearly the same as the 119 years derived by B. H. Dawson as long ago as 1924. Its true orbit, have the dates for apastron and periastron as 1938 and 1998, respectively. Currently the stars are widening (2007). In the apparent orbit, both stars were farthest apart (2.50 arcsec) in 1940 and they will be closest again in 1992. The secondary will be due south of the primary in 1973, with the position angle 180°. Both have the spectra classes of F8V.

Δ225/ Δ225 AB / HU 1654BC (19124-5148) is listed as a triple within the small and faint constellation of Telescopium. This pair can be located easily some 1.1°ENE (PA 60°) from the yellowish coloured, 5.2 magnitude ρ Tel / Rho Tel / HIP 93815 / SAO 245921 / PPM 347432 (19063-5220). Δ225 AB is listed as 7.0v and 8.4v (7.06V and 8.42V) whose components are divided by 70.2 arcsec along PA 250°. This makes the two visible in apertures as low as 5cm or binoculars. Little change has been observed in the positions except perhaps for a slight widening in separation. This orange and yellowish pair is fairly attractive that seemed slightly better in the 20cm at low magnification.

Another component is 11.0 which was discovered by Hussey in 1914. This fainter star is clearly obvious in apertures between 10.5cm and 15cm. - hidden mainly by the companion’ brightness. The IDS 63 to the WDS 04 continues to give the 1914 positions as 29.7 arcsec along PA 80° that is presumably measured from the Δ225 B component. There is some quite wrong with this designation because the AC component corresponds to the correct value and not the BC one - unless of course there has been quite significantly proper motion.

Proper motions suggest the two brightest AB stars are associated. However, the motion of the C star, at least from the calculated measures. These changes are far more significant and much larger. This suggests C is really a general field star. Furthermore, a small problem exists with the mutual parallaxes of AB as given by Hipparcos whose errors don’t quite overlap.

U Sge / U Sagittae (19188+1937) has one of the deepest eclipses than most of the known EA eclipsing binaries, which is easily observable even in binoculars. It can be found 2.8°W of the centre of the bright stellar group called Collinder 399, that contains the three brightest stars of 4, 5 and 7 Vulpeculae. It is also some 0.7°NE from the yellowish 5th magnitude star, 9 Vulpeculae.

U Sge’s brightness varies between 6.58v and 9.1v over 3.380626 days (3 days 09 h 08.1m). Its deepest or primary eclipse drops significantly because of the presence of a much cooler companion. The primary eclipse lasts about 3.5 hours with the magnitude changing twenty minutes either side of main eclipse falling near the rate of about 0.15 magnitudes per minute! Primary total eclipse lasts about 1.6 hours, before the brightness again begins to increase. Visual observations when compared before the primary eclipse may notice some colour change in the star. U Sge’s secondary ‘occultation’ eclipse is relatively minor by spanning only 0.1 magnitudes.

U Sge from the latest analysed light curve and obtained spectra reveals both stars have the respective masses of 7.4 M⊚ and 2.2 M⊚ - in the mass ratio of about 3:1. Previous calculations had yielded smaller values for each star. The literature (I.e. Plavic (1973)) still continues to state that U Sge is an unusual system because it defies many of the known assumptions - giving us the warning of the problems associated with all photometric systems.

We calculate the actual distance between each star as 14 million kilometres, with each star having the respective diameters of 5 million and 7 million kilometres. The primary has the luminosity 140 L⊚ with the secondary only 11 L⊚. Unusually, there is some evidence from the small fluctuations seen in the light curve - explained by the primary having a dusty gas cloud orbiting within some circumstellar disk.

Spectral class for the sub-giant primary is B8 III, while the secondary was originally stated as a sub-giant G2 IV-III. Recent literature now tends towards perhaps a K-class star. Temperatures of the two stars are estimated to be 10 240K and 4 720K, respectively. Distance is presently estimated as 220pc. or 720 ly.

The well separated pair Σ2504 lies some 0.7° away, as stated in Bunham’s Celestial Handbook Vol.3, pg.1528. Both make good comparison stars, having respective magnitudes of 7.0 and 8.7 and both about the U Sge’s variability. Separation of the pair is 8.9 arcsec, and this has only slightly increased since F.G. Struve discovery in 1830.

Δ226 / β1 Sgr / Beta (1) Sgr / Arkab (19226-4428) is placed directly south under the asterism known as The Teapot in southern Sagittarius being either 34′E of the CrA border and 48′N of the Telescopium one. β¹ and β² Sgr are of near equal magnitude (4.2v and 4.3v) and in actuality separated by some 21.4 arcmin through PA 164°. Both Alpha Sgr nor β¹ or β² are not featured i n Burnham’s extended descriptions.

β¹ Sgr is listed the 3.96V star; HIP 95241 / SAO 229646 / PPM 325041, but through a telescope, the star is revealed as the pair Δ226. This duo is fairly easy to resolved in 7.5cm and in much larger telescopes is a complete delight. Both stars since discovery in 1826 have remained almost fixed each being separated by 29.6 arcsec along PA 77°. When observed on the meridian - just 10°S of my local zenith, I thought were very pale blue and white, but several references state they think the primary blue, white to yellow and the secondary ashy, white or blue! For example, Eugene (Eddy) O’Conner, in a private communication in 2001 says sees “The primary is a brilliant white and the companion is wide and a dazzling blue colour.” The range of colours is to me extraordinarily large for such a prominent pair. Earlier references say the spectral classes are B9V and A0V, suggesting that the differences in surface temperatures were only small (K and K). However, later references including the WDS04. give the secondary as a cooler A0. Strangely, AOST1 says the spectral class of the companion is A3, which I could not identify from the available SIMBAD data.

Observational Descriptions

Unlike many southern pairs, I have read a number of different observational descriptions. Oddly missing from Innes southern description and notes in Webb’s “Celestial Objects for Common Telescopes.” (1961) (COCT2)

1) Eugene (Eddy) O’Conner, from the same reference above, states on β1 Sgr;

“[Δ226] is a delightful double to end the night and is perfect for small telescopes. My map confuses me with the variety of names for this star. No matter this is it a stunner! It is the most westerly of Sagittarius’s dazzling doubles…”

2) E.J Hartung (AOST1) (#862) says;

“…no real change…but they probably form a physical system. Bright pale yellow and ashy white…”