"The Nightmare Continues..."

(Note: NSP 15 continues from "Universe" October 1998)

This part includes a moderately tough planetary in a northern boundary of Circinus with Centaurus. I personally like this region of the sky because it contains so many interesting objects and there are numerous bright stars to locate these tempting objects. Rough in the next few issues we will cover the area surrounding the "square" of sky of Alpha and Beta Centauri, Alpha Circini and the north-eastern edge of the "Black Magellanic Cloud" the Coal Sack. First is He2-103 which I selected because of its close proximity to the Circinus Dwarf Galaxy. As you may have noticed throughout this series, most of the NSP are located near bright objects - reflected by my perhaps "more lazier" methods of finding objects via star hopping. I have sometimes found over the years exclusively use of setting circles can only make you miss out on some of the more interesting objects surrounding your particular target. (Note: The most challenging deep-sky that I know, and not obeying this rule is the dread and hard southern Pavo PNe, He2-434 (NSP6).) If you do look at these planetaries, an O-III or UHC filter will prove a godsend.

The field teems with a scattering of moderately faint stars. I could just see the small disk of He2-103 using both averted vision and high power in a 30cm., but this wasn't easy. Using a moderate to low magnifications it became impossible to see, likely because of the overwhelming brightness of the sky background. He2-103 subtends a diameter of 20.0"sec.arc., and has a visual magnitude of 14.0 (13.9ph.), first obtained from photographic measures made by Cahn/Kaler. (AJ.Supp., 223,319-368 (1971)) I found the use of an O-III made only a slight improvement to the faint but featureless smudge. Looking at the PNe's data in the ESO-Strasbourg PNe Catalogue (1996), I suspect it would appear much better in a UHC filter than a O-III filter. Apertures greater than 35cm. should have little trouble seeing it, though I would firmly recommend that observers attempt this from a dark sky site.

The scant observations available on the central star has not found any magnitude information, though it is suspected to be of spectral class O VI. Overall it is presently moving towards us at -30±2.0kms^-1, while the expansion velocity of the gas is estimated to be less than 6.0kms^-1. Other than a NIR magnitude determination, little information has been obtained from other studies. Statistical distances average about 2.8kpc., which likely accounts for the planetaries faintness in a fairly dusty region of space.

Overall a challenging object for larger apertures.

NGC 5288 / Cr 278 (13487-6440) is a moderately bright star cluster with only a few stars visible, and is not listed in AOST1 or 2 nor in Sky Atlas 2000.0. The cluster is 1.8^O due east of Sa2-103 - about halfway between the PNe and the eastern edge of the Coal Sack. It can be found in the NE corner of Circinus, in an odd-looking small piece of square sky once manufactured by Delaporte in 1928 to accommodate the two eclipsing binaries of T and V Circini - thus keeping them within Circinus' boundaries.

Classed as 2 1 p -, NGC 5288 contains some 25 stars in a compact 4.0'min.arc. Some debate exist on whether this is a cluster or not - perhaps because of its faintness. When John Herschel observed it in 1835, he claimed to see a "...very compact knot of Milky Way", and estimated the mean stellar magnitude as 14th, though the RNGC gives a mean magnitude closer to 12th.

In a 20cm., NGC 5288 looks nothing at all like Herschel's description. Just 2.6' away west and slightly south of the cluster's heart, is a 7.8 orangish star HIP 67356/ HD 119941 (13483-6441), as Herschel describes "... a star 8th magnitude precedes". Another 8th magnitude star 14' preceding the cluster. This is reddish-orange 7.8 magnitude star HIP 67226/ HD119661 (13465-6441). Herschel fails to mention this rather fairly prominent field star in his description of the cluster. Is Herschel indicting that this is the preceding star in his description? (HIP 67226 is the same field as the cluster.) How John Herschel twice found this cluster remains a bit of a mystery, as I expect a 30cm. might have some trouble seeing more than a dozen stars.

At the given position of NGC 5288, there are only two 16th mag. stars indicated in Megastar 4.0, and I could just see in a 20cm. perhaps a handful more. Attached is the STScI image, that shows the cluster and the bright star in the field is HIP 67356.

T Circini (13434-6528) is one of the most prominent of the southern eclipsing binaries, mainly because of the significant 1.5 magnitude drop in brightness during primary eclipse. Known as an evolved Algol semi-detached eclipsing binary, the magnitude at maximum is 9.3 falling to 10.6. Beginning at mid-primary eclipse on the 15th August 1938 (JDE=2429095.586), the fairly exacting period is 03h 07m 09m 44.35s (3.298430days). The time spent during eclipses is 13% of the period, some 10h 17m 28.01s, with the primary eclipse lasting half this time - 5hr 08m 44s, dropping 1.5 magnitudes in 1 hr 28m. The entire stellar total eclipse lasts 3hr 40m. As the stars are so close, gravitational forces has distorted the stars into "teardrop" shapes. As the surfaces are non-circular, the observed light curve appears a bit more "smoothed" instead of the "jagged".

Looking at the radii and mass of the two stars, we can see the so-called Algol Paradox at play - where the lesser mass star seems to be the most evolved, seemingly acting "against the face" of stellar evolution theory. In fact is was the primary which first to evolve. As it swelled into a red giant it reached its critical volume and fills its so-called Roche Lobe. The hot surface gas has nowhere to go but to transfer mass to the secondary. In time, the secondary ages, hastened by the additional added mass, and so begins to become a red giant. Again the critical Roche Lobe is exceeded, and the surface material of the secondary is "recycled' back into the primary's mass. Here we reach the current status of T Cir, where a large percentage of the mass has now flowed from the secondary back into its companion.

All eclipsing binaries transferring mass show some effects of their true celestial marriage. So intertwined have they become, that it becomes difficult to tell by looking at the spectra the chemical evolution of each star. Eventually both stars completely fill their Roche Lobes, causing material along the critical surface of both stars to begin being discarded into interstellar space. One star eventually become a white dwarf and its companion a red giant.

The future of these Algol-binaries eclipsing binaries is most likely a binary white dwarf. But for the closest of systems their demise is a little less certain. In some scenarios it is possible that they could become either dwarf novae, novae, FK Coma Berenices variables (merging white dwarfs) or even R Corona Borealis variables (those "anti-novae" variables that suddenly drop by up to ten magnitudes.) For those who have a combined masses exceed 1.44 (the Chandrasekhar Limit) and have begin to merge together, there demise can end ultra-violently - ending as a catastrophic Type I supernovae.

Y Circini (13 392-6507) is another eclipsing binary which has very little observational background. This system lies on the border between Circinus and Musca. Although stated as "SD" - Semi Detached, this status is certainly very tentative. Variations are given between 10.8 and 11.8, in a period of 3.17 days and the spectral type is estimated to be Ap.

The Circinus Dwarf Galaxy / ESO 97-13 or ESO 97-G13/ PGC 50779 (14131-6530) is a field's step away, being the only galaxy within cooee in this part of the sky. Located 1^O SE of Sa2-102 along PA 129^O, it appears on Map 452 in Uranometria 2000.0 and is listed as object # 631 in AOST2, with a AAT Schmidt image on pg. 209.

Discovered in 1977 using the Uppsala Schmidt telescope at Mt. Stromlo, this galaxy shows a band of obscuring dust swathing across the very southern parts of the disk - however, this is invisible in all amateur astro's telescopes.

In a 20cm., and possibly even in a 15cm., this ovoid 2'x1.5' "smudge" is aligned along PA 40^O, appearing as a featureless disk in a whole heap of field stars. Measured is a 12.1 'B' magnitude with a high surface brightness of 13.0. Photographical the size of this small spiral galaxy extends 6.9'x3.0'. Spectra reveals the galaxies proximity, as the radial velocity is a tiny 380kms^-1 way from us.

The Circinus Dwarf Galaxy is surprisingly bright for an galaxy within the Milky Way, especially where you would expect obscuration by intervening gas to 'exterminate' its considerable brightness. The literature quotes that this dwarf galaxy appears in a convenient less dense corridor of Milky Way's, but there is no significant evidence to support this except for the "highish" B-V magnitude of 1.46. It is likely if this galaxy appeared away from the galactic plane, it would rate on amateur lists of as one of the better of the deep-sky galaxies in the southern skies. For observers to see this, you may have to wait a long time. I estimate some 30 million years would have to pass for the Sun to orbit the Milky Way sufficiently to bring it into view. AOST2 quotes the distance as 4.0 Mpc. (13 million lty.), suggesting that it is well away from our Milky Way conglomeration of companion galaxies.