Intriguing multiple stars in Leo, Virgo and Scorpius

[starfinder]

Faced with our dark-sky challenged urban blight, I decided to do some multiple star observations in the past week and saw some very intriguing double and multiple star groupings in Leo, Virgo and Scorpius.


Here are some highlights and comments.

Observations were with an 8" SCT (LX90) using 14mm and 6.7mm eyepieces, at times together with 2x and 3x barlows stacked, for magnifications of 143x, 300x, 600x, a crazy 900x and a madness of madness 1800x (more on these powers later).

Do try to see them too, and post your own impressions here!


Leo. Its up high in the East these days in the evening. Saturn is currently in a dog-fight with Regulus (actually a cat-fight).

Algieba (gamma-Leonis). Close colour double of 4" (arc seconds) separation, mag 2.2 and 3.5. Described as "One of the finest in the heavens". Both stars are said to be golden-yellow, but I sometimes see the fainter one as light bluish-white (this bluish colour was seen even when the brighter is star left out of the edge of the eyepiece's field of view.)


I remember once viewing this jewel in the eyepiece at Telok Sari a few years back whilst doing an Auto-Align procedure. I was stunned as I had not seen it before then in an eyepiece, or had seen it before but forgotten that I did. Anyway, this one's [glow=red]wow factor [/glow]comes with a money-back satisfaction guarantee; no need to produce receipts! (beat that Carrefour)


Iota-Leonis. A very close pair of whitish stars of mag 4.0 and 6.7, separated by a mere 1.8". Since one is about 10x brighter than the other and they are only 1.8" apart, I could not see the fainter one at first, until I used very high magnifications of 600x and above. Even then, they were a mere hair's-breath apart. After seeing the fainter one, I think I could see it at 300x since I knew where to look. The fainter star has a light-blue hue if I recall correctly.

According to the authors in Stars and Planets (Princeton Field Guides), iota-Leonis has a 186 year orbit and are currently moving apart. Until the year 2010, about 100mm aperture and above would be needed to separate them, after which they become progessively easier.


Virgo. Up at about 9pm in the East these days.

Porrima (gamma-Virginis). With this one, I really had to push the SCT's complex optics to the limit with mind-boggling powers in order to split it.

Porrima shines at mag 2.7, but it actually consists of two white components each of mag 3.5. They were closest in 2005, when 250mm of apeture was needed to separate them. Apparently, by 2010, they would be wide apart enough for 100mm apeture to split.

They are only only 0.4" apart. By contrast, the planets such as Mars, Jupiter and Saturn have apparent widths of about 20-40", so 0.4" is really close, and a cigar too.

Armed with a modest 8" primary, and a not-so-modest 14mm XL (ahem!) at 143x, I could not discern Porrima as a double star. Next, I upped the ante to meet the close challenge: out came the 6.7mm UWA from its protective bottle. Now I could discern some elogation and separation in the star, like it had a split personality.

That was not good enough to confirm it. So, disregarding conventional wisdom, I popped in a 3x apo barlow for 900x. Now I could see the two components' Airy disks clearly separated, but with the untidy SCT diffraction rings still overlapping. The separation was less than the gap between the A-ring and the B-ring: Cassini's division looked wide by comparison.

Finally, as I had not done this before, I decided to try something crazy. [glow=red]I stacked the 3x apo barlow with a 2x apo with the 6.7mm, for a grand total magnification of 1800x[/glow]. Amazingly, the image still held-up, showing two blurry but distinct Airy disks with a larger gap in between. (Warning to kids: please try these crazy powers only under close adult supervision)


Scorpius. Its well-placed in the sky at around 1am these days in the Southeast.

Antares (alpha-Scorpii). Its easy to forget that this famous star is a close colour and brightness contrast double, and I had to be reminded of this by reading about it again last night.

The primary star, Antares itself, is a "red" supergiant and is a semi-regular variable of mag 0.9-1.2. Its bluish-white companion resides at a mere 2.5" away (from our Vantage Point) and shines weakly at only mag 5.4. That means that the primary is about 60 times brighter than the secondary. According to the Princeton guide, the secondary requires at least 75mm of aperture and steady atmospheric conditions to be seen against the primary's glare. I managed to split them at about 600x I think.

The pairing is really a neat sight indeed!


Graffias (beta-Scorpii). Mags 2.6 and 4.9, separation 14", bluish-white pairing.


v (Nu) Scorpii. I had not known that there is [glow=red]another Double-Double[/glow] apart from the one in Lyra, until I read about it last night. Well, this one in Scorpius is just as good if not even better than its more famous Northern cousin.

The two main pairs shine at mag 4.0 and 6.3, widely spaced 41" apart. However, at high magnifications it can be seen that each is itself a double star. The brighter one has two components of mag 4.3 and 6.8 at only 0.9" apart and requiring 100mm aperture to split. The fainter one's components are of mag 6.4 and 7.8 at 2.3" apart.

Nu-Scorpii is certainly quite a visual treat and a good challenge to split. Definitely a keeper.


Xi-Scorpii and Struve 1999 I can't reproduce Xi here, but this Greek letter looks quite like Scorpius itself. Xi-Scorpii (16h 04m, -11.4deg) and Struve 1999 is a double-triple star grouping which have an interesting almost symmetrical formation. Go have a look!

The two main triple-groupings are about 280" apart and are gravitationally connected to each other, so the guide book says. One is Struve 1999. The other is Xi-Scorpii itself, which at first looks like a double star, but the brighter one is actually itslef a double of mag 4.8 and 5.1 needing 150mm apeture to split, making it a Double-Double-Single.

Therefore the whole lot is a [glow=red]Double-Triple-Double-Double-Single [/glow]tongue-twister. For the DSO faint-fuzzy averted-vision lovers out there: you aint' seen nothin' yet!



Some general Observations

1. I discovered that unlike observing the planets, where there is a practical magnification limit of about 300-400x after which the image degrades so as to become useless, with multiple star observing, there is utility in really increasing the power to extremely high levels of 600x-1800x if need be, even though the resulting images are soft.

It may be because stars are point sources of light, and the purpose of using very high powers is just to split the stars widely so as to see the separation clearly, as opposed to seeing variations and low-contrast details on the planets.

I would add that being able to push up to very high powers depends on the ability of the optics to handle it, I should think, especially in relation to chromatic aberration. Thus probably only mirror-based and apo-refractors would be able to handle such high powers. Plus aperture does count too.


2. Multiple star observing is an aspect of amateur astronomy which is not much hindered by light pollution, in a similar way to planetary and lunar observation. This makes it a suitable subject of visual study in Singapore, unlike most fainter DSOs such as galaxies, globulars and most nebulae. So, [fade]when we are Mersing-deprived[/fade], there is a fall-back!


3. If you would like to know how much brighter a star of one magnitude number is from another, you can use this useful on-line calculator:
http://www.1728.com/magntude.htm



If anyone else has made observations of the above multiple stars, please post your comments here. Plus if you know of other gems currently in our skies, please post too!

*****


References:

Stars and Planets (Princeton Field Guides). Ian Ripath & Wil Tirion, 2007 edition.

Double and Multiple Stars and How to Observe Them. James Mullaney, 2005.