Southern Doubles, Stars and Variables
10 Mar 2009
RA : 04h
Dec : -30° to -90°
Constellations : Eri, Cae, Hor, Pic, Dor, Ret, Hyi, Men, Oct.
Best Observed : Oct - Mar (Text Ordered by RA)
RA : 04h
Dec : -30° to -90°
DS 00h 01h 02h 03h 04h 05h 06h 07h 08h 09h 10h 11h
NEW 12h 13h 14h 15h 16h 17h 18h 19h 20h 21h 22h 23h

Δ17 / I269BC / I269BD Ret
GAL 364 Eri
BRT 2634 Eri
HJ 3679 AB&AC/ R Dor
HJ 3686 Dor
COR 23 Pic
ι Pic / Δ18 Pic

R Dor / HJ 3679 AB&AC
R Pic

None Listed

ω Aur / Σ616 Aur
NGC 1515/ 1515A Dor

Positions given as;
I.e. (13583-6018), are;
13h 58.3m
-60° 15'
This follows the current
WDS Conventions.

or arcsec
In arc seconds or
or arcmin
In arc minutes or
mas - milli arc seconds

( ° ) Angle in degrees.
Measured from
North through East

v - visual (naked-eye)
p - photographic
V - Photometric Visual
B - Photometric Blue
MV - Absolute @ 10pc.

pc. - parsecs
ly. - light-years
AU - Astronomical Unit


T: Periastron (yr.)
P: Period (yr.)
a: Semi-Major Axis (arc sec.)
e: Eccentricity
i: Inclination
Ω: Orbital Node (°)
ω: Angle True Orbit (°)

R.A. 04 Hours

Δ17 / I269BC-BD (04010-5424) is a uneventful system containing four stars that lies in northern Reticulum some 4.9°W of Alpha Doradus. James Dunlop saw only a triple, with the respective separations of 63 and 41 arcsec, with the main pair aligned at the angle of 49° 23'sf equivalent to PA 139.4°. No position angle is given for the third star, but it is identified as I 269 BD in present catalogues. (Should this be really designated Δ17 D ?) He gave all as 7, 8 and 8 magnitude describing it as; A triangle of stars.

Today, Δ17 AB is a brightish equally white pair being quite attractive in small telescopes, being currently separated by 64.2 arcsec along PA 142° with magnitudes of 7.7 and 8.2. Since discovery in 1826, both stars have slightly widened by 1.3 to 1.5 arcsec while the PA has increased by merely +2°. Looking at the proper motions of the two it is likely that of Δ17 is an optical pair.

Closer inspection finds that there are another two components. The B star is again double, showing the companion as a 11.57 magnitude star some 3.5 arcsec along an extrapolated PA of 77° - some 10° less than when discovered in 1898. This is the pair I 269BC, and it is likely that the two are gravitationally bound. I saw both as white in 20cm. Another star, about one magnitude fainter at magnitude than the C star lies some 27.7 arcsec away at PA 196°. This is I 269 BD and this pair is visible in 20cm, and even possibly 15cm with care and good optics. Little has changed in the components positions since found by Innes in 1900, and the positions seem right, although few measures have been obtained. The alignment is along PA 196°, and it is unknown if this star is attached BC or even the A star. These latter components are both white.

NGC 1515 / NGC 1515A (04041-5406) also shares Δ17 in a wide telescope field with the moderately bright and elongated spiral galaxy which both appear in nearby Dorado. Lying 32'NE of Δ17 finds NGC 1515 which is listed as a SXS4 type aligned as an elongated gossamer almost in a north-south direction. It covers about 5.2'x1.1' of sky and is about half of this in 20cm. At 11.03v or 12.6B magnitude and surface brightness of 12.6 this galaxy is easily visible in 10.5cm in dark skies.

NGC 1515A is a better challenge is the companion galaxy which is 1.8' WSW (PA 243°) of NGC 1515. Just visible in 20cm, and better in 25cm, it appears about 40"x30"arcsec in size as a tiny smudge without any visible details. The RC3 says this is a spiral of type SBR3. It is almost certain that this galaxy is not attached to the much larger galaxy as the radial velocity is +13 265kms-1 thus giving D as 204Mpc and ten times the distance of NGC 1515.
Not mentioned in AOST2 for some reason, it is still worth seeking out. Sky Atlas 2000.0 gives the RV as 884kms-1 while the RC3 gives +1 216kms-1. If we take the latter value, then D is 19Mpc.

GAL 364 (04140-1222) is a dainty pair located in a starry field in Eridanus some 21'N of NGC 1535. Discovered in 1871 by J.Gallo, the pair is near equal brightness at magnitudes 8.9 and 9.0. Separation between the AB components is 21.1 arcsec at PA 45°. No change has been observed since the first measures in 1901.

BRT 2634 (04160-1244) is a very faint white pair in Eridanus that is so easy to find that I had to include it. BRT 2634 lies 22' due east of NGC 1535. Set the telescope using medium magnification then glide the telescope by the one or two star fields. Both stars are both 12.0 mag. Separation of the two stars is 3.1 arcsec at PA 104°. Again, little has changed in the pair since the discovery by S.G. Barton.

R Dor / HJ 3679 AB / HJ 3679 AC (04368-6205) is a semi-regular (SR) variable star that varies between 4.8 and 6.6 magnitude in a rough period of 338 days. R Dor is position merely 2.2' inside the Dorado border with Reticulum. It is best to use the orangery-red M2III 4.6 magnitude star δ Ret / Delta Reticuli (03587-6124) and move the telescope 4.5°ESE (PA 102°) or alternatively move 2.6°E (PA 86°) of 3.3 magnitude α Ret / Alpha Reticuli / HIP 19780 / SAO 248969 (04144-6228).

R Dor has a rich red almost vermillion colouration and was classed as both EsB 94 and EsB 95 in the Espin-Birminghams Stars With Remarkable Spectra Catalogue. The error seems to have been a simple duplication being identified with HR 1492. In the GVCS classification for the variable is designated as "R Dor 0435-62" in 1900 co-ordinates and appears on RASNZ Series 3. Chart No. 78. Spectrum is M8 IIIq:e

Hartung in AOST1&2 describes the field and variable of R Dor as;

This orange-crimson star ornaments a field sown with less bright stars, some quite close to it. The star is an irregular Mira-type variable of period averaging 338 days and has a fine spectrum crossed by many dark and bright lines and bands. 10.5cm will show some of these near the stars maximum.

R Dor also has two fainter companions. HJ 3679 AC is of 11.0 magnitude that lies 24.5 arcsec along PA 124°. HJ 3679 AB is of 11.9 magnitude that lies 38.4 arcsec along PA 13°.

A distance from the Hipparcos parallax of 16.02±0.69 mas gives 62.42±2.69pc. or 203.6±8.78 ly. Proper motions show that R Hor is moving towards the southwest at the rate of pmRA; -68.46±0.73 pmDec; -72.22±0.78, calculating a common proper motion of 99.51mas per year along PA 226.5°.

[NOTE: HIP 21479 / PPM 354226 / SAO 249066 / GSC 8880:1071 Mag(v) is 5.59 and the B-V of +1.500 Spect: M8e]

HJ 3686 (04417-6113) lies 1.0°NNE from R Dor (PA 30°) or by moving the telescope 5.1° due east (PA 91°) from the red 4.6 magnitude δ Ret / Delta Reticuli (03587-6124). The component magnitudes are a near equal 7.7 and 7.8 (8.37V and 8.45V) for the whitish pair each separated by 7.2 arcsec along PA 221°. Dissimilar proper motions mean that this is likely an optical double. Little change has been seen with HJ 3686. Spectral classes are described as A1/2V+A. This is a nice pair in a starkly bare place of stellar objects.

COR 23 / CorO 23 (04419-4750) is a bright pair discovered at the Cordoba Observatory in 1896, and considering its brightness, it is unlucky that neither Dunlop, Rümker, J. Herschel, or Russell missed it. It appears 2°N of Lambda Pictoris in a small square of sky in western Pictor that was added too just to accommodate the variable R Pictoris (See Below) The respective magnitudes are 7.4 and 9.9, and the duo is separated by 3.6 arcsec and has remained without any change since first found. The PA is presently 219°, which has continued to reduce from 234° some 106 years ago (2002). I saw the primary as yellow and the companion as white. I have not seen this pair discussed anywhere in the literature - a question that I cannot figure-out why. I have seen much poorer pairs than this being discussed and venerated and this one outstrips many of the Struve pairs that I have seen. This is one of the unrecognised southern astronomical delights. A must see!

R Pic (04462-4915) is an semi-regular SR variable whose average variations change between 6.4 and 10.1 in the period of 170.9 days. This orangery-red star has an observed spectral class also varies during the cycle between M1IIe-M4II.e. R Pic can be found 2.7°W of 5.4 magnitude η1 Pic / Eta (1) Pictoris or alternatively 1.3°NNE (PA 24°) from orange 5.3 magnitude Lambda Pictoris. The RASNZ Variable Chart number is 9 and R Pic is designated in the variable star scheme as R Pic 0443-49.

Δ18 / Iota (ι) Pic (04509-5328) is a wonderful bright light yellow pair with about a magnitude difference between the components, and unlikely most Dunlop pairs, the separation is reasonably close. I think Δ18 could be considered a paler mimic of the bright p Eridani (Δ5), however, Russell described this pair as "Both straw yellow." The duo can be found some 5.4°SWW of Theta Pictoris /Δ20 (See Below) Since discovery the pair has changed from PA only 2° to todays 60°, while the separation is the same distance of 12.5 arcsec.

The spectral class of the stars are F0IV and F4V. Some evidence suggests that the primary shows an unusual variable radial velocity. This suggesting the star maybe a spectroscopic binary or that there is some turbulence in the stellar atmosphere. Yet the spectral class is a little to cool to understand changes in current stellar evolution theory. Also, no true variability in brightness has been found. Both stars might be slightly younger than the Sun. Distance is about 37pc. Looking at the significant largish proper motions the stars seem connected, but if this is so, then the period is likely to be very long. A great pair for small telescopes.

Omega (ω) Aurigae / Σ616 (04593+3753) is a brilliant pair to observe, whose name just seems to just roll of the tounge! Magnitudes of the duo are 5.1 and 8.1, being separated by 4.6 arcsec and perfectly aligned north-south. Discovered by F.G.W.Struve in 1822, and is catalogued as STF 616 or Σ616. With care any 7.5cm should just resolve this stunning pair in a faint, in a very starry field. A 10.5cm telescope however, shoould have no problems at all.

I saw the colours of the two stars as having quite different shades of yellow, but thought the primary star was strongly influencing the perceived colour of the secondary; and applying some imagination, saw the stars as white and gold. This pair has slowly been reducing in separation in the last 180-odd years, and is likely a binary of a long but undetermined period.

Southern Astronomical Delights”
© (2009)
10 Mar 2009