Southern Doubles, Stars and Variables
SOUTHERN ASTRONOMICAL DELIGHTS : Presented by Andrew James
|PAGE DS 017
10 Mar 2009
|RA : 17h
Dec : -30° to -90°
Constellations : Oph, Sco, Ara, Pav, TrA, Aps, Oct.
Best Observed : May - Sep (Text Ordered by RA)
|RA : 17h
Dec : -30° to -90°
SELECTED SOUTHERN DOUBLES and VARIABLES
These four (4) sets of data alone show linear motion suggesting that the components are not attached.
The linear prediction calculator gives the following results;
NOTE: These ‘predictions’ will likely be fairly accurate if the pair is unattached.
Δ214 A is listed as the star HIP 84248/ SAO 253827 / PPM 362557 with a B-V of+1.070 and the spectral class of K0III-IV. Δ214 B is T9064:3629:1, being listed as 8.75 magnitude, with a B-V of +0.228. I notice here that the white/ greenish? colours seen in the telescope do not match were well with the given B-V value. I can only assume that some colour contrast effect is prevalent here.
Looking at the parallaxes of A: 9.98±0.66 (Hipparcos and B: -11.90±8.60 (Tycho) it could be assumed that both stars appearing at similar distances might infer they are attached. Distances, incidentally, are A: 100±7pc. (327±22 ly.) and B: 84pc.
Yet looking at the available positional data, the proper motion of the primary are given in the Hipparcos Catalogue as pmRA; -156.26±0.49mas.yr-1 and Dec -90.10±0.55mas.yr-1. However, Δ214 B appears only in the Tycho but is not listed in the Hipparcos one. The Tycho data gives quite poor quality data here (pmRA; -34.90±11.90 : pmDec; -2.70±6.80.) In comparison with the data, there is significantly large difference between the two but it seems unlikely that these two stars are genuinely attached.
ZZ Her / u Herculis / 68 Her / OΣ328 (17173+3306) is the second brightest northern eclipsing binary - second only to the eclipsing binary Beta Persei or Algol. ZZ Her is easily located by the naked eye some 5.5°S of the bright orange 3.16 magnitude star Pi (π) Herculis (67 Her) and varies between 4.6p and 5.3p magnitude over 2.0510 days. Burnham’s Celestial Handbook Vol.2 pg.956 listed the star as 68 Her, but gives the magnitude range as slightly brighter 4.7v to 5.4v. Spectral classes have been found to be B1.5 Vp and B5 III, respectively.
Both stars are separated by 10.2 million kilometres, each having the individual diameters of 3.2 and 3.1 million kilometres. By luminosity, the primary is 1 159 times the solar output, while the secondary is 295 times. Both are B-spectral type stars, with respective temperatures of 15 780 and 11 450K. Masses of the stars are 7.2 M⊚ and 2.9 M⊚.
There is some indication that the secondary has exceeded its Roche Lobe in the past, and has already bestowed most of its mass to the primary. This is a clear example of the so-called Algol paradox, with the primary being the smaller in mass although it is the most evolved component in the system. The shape of the secondary is still likely a teardrop, with the primary is only slightly distorted by the gravitational field. Distance is 220pc.or 720 ly.
u Herculis is also the double star OΣ328 / STT 328, whose 10th magnitude blue-white to greenish companion is separated by 4.4 arcsec along PA 59°. Little has changed in the positions since Otto Struve’s discovery in 1843. It is likely that the stars are physically associated with the close eclipsing binary.
DW Aps / HIP 85095 / SAO 253891 / PPM 362664 (17235-6756) lies 1.2° (PA 217°) from Δ224 or alternatively 13' (PA 130°) from the 4.8 magnitude yellow-orange star Zeta Apodis. The field of this light bluish star is marked by many faint stars visible in 20cm but very few through 15cm or less. DW Aps is an Algol-type (β Lyr) eclipsing binary of the semi-detached [SD] type that displays moderately sized variations compared to some other eclipsing binaries. Changes are between 7.9p and 9.1p in the period of 2.312950 days. DW Aps is the only established eclipsing binary with well known parameters in the constellation Apus. The fall of 1.2 magnitudes during the primary eclipse occurs over 7% (3h 53m 09s or 0.1619065 days) of the period while the entire primary eclipse is twice this (14%) (0.323813 days) of the entire cycle. The current given epoch is 2439209.502 [25th March 1966 (02h 53m U.T.)] Spectral class is B6III.
A ‘SD’ or semi-detached systems are those which have the surface of the less massive component being close to its inner Roche lobe.
Based on the collected data, the separation of the two stars is 12.58 R⊚ (8.766 million km) whose component sizes is ‘A’ 2.26 R⊚ (1.57 million km.) and ‘B’ 3.78 R⊚ (2.63 million km), respectively, being based on the solar radius of 696 850 km. Luminosities are 38.81L⊚ and 13.37L⊚ times that of the Sun. Physically, both stars have not at present filled there potential Roche lobes, even though it is highly likely this has occurred in the past. Calculation suggests this is ‘A’ 44% and ‘B’ 86%.
Temperatures are given as 9 620K and 5 750K, while the component masses are ‘A’ 2.93M⊚ and ‘B’ 2.17M⊚. (ΣM⊚ of 5.00) Spectral type is B9III and A0+. (See Graphical Representation.)
Unfortunately the derived parallaxes of 3.20 mas is small, making these parameters with some uncertainty.
1. “A Catalogue of Parameters for Eclipsing Binaries”. Brancewiez, H.K. and Dworak, T.Z.; ACTA Astronomica, 30, 4, p.508 (1980)
|“Southern Astronomical Delights”
10 Mar 2009