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Southern Cross - May 2001

• Musca by Steve Crouch
• Searching for Planets with Infrared Spectroscopy by Len Williamson
• The Galaxies of Sextans by Jenni Kay
• Deep Sky Observing with the Webb Society by Jenni Kay

Musca

Steve Crouch

Musca is a small constellation to the south of the Southern Cross. There is a fairly good assortment of deep sky objects here with planetary nebulae being predominant. Obscuration from the Milky Way means that observable galaxies are almost absent but there is at least one still worth hunting down.

My observations were made using a C14 and a variety of eyepieces from my backyard site in outer Canberra (most of the time I used a 35 mm Panoptic which gives about 112x). I rated the seeing at perhaps ANT III with the transparency starting out as poor to average but improving later in the evening.

1. Double Stars

The first one observed was h 4432 (RA 11 23.4 Dec.-64 57) which with a separation of 2.4" and white components of magnitudes 5.4 and 6.6 was just separable with the 35 mm eyepiece.

CorO 130 (11 51.9 -65 12) is a bit more challenging. The white components of 5.2 and 7.4 are only separated by 1.8" so a bit more magnification is required. I obtained good separation with a 12mm eyepiece although the pair did appear elongated with the 35 mm in moments of good seeing.

Theta Muscae (13 08.1 -65 18) with a separation of 5.3" is a nice unequal pair with a brighter yellowish component of magnitude 5.7 and a fainter whitish one at 7.7.

2. Bright Nebulae

IC 2966 (11 50.5, -64 54) is listed as a bright nebula but I did not observe it. There probably isn't anything much there as the second edition of Hartung fails to mention it.

3. Open Clusters

None of the Musca open clusters that I observed were particularly effective. The best one was NGC 4815 (12 58, -64 57.7) which, with the 35 mm eyepiece, appeared roughly elliptical in shape and contained about 20 faint stars. Two E-W aligned field stars are superimposed.

I mention CR 269 (13 22.6 -66 07) and CR 277 (13 48.7 -66 05) only because the best object in Musca, the planetary nebula NGC 5189, lies almost exactly midway between them. CR 269 is a very poor cluster and CR 277 not much better. Although marked on Uranometria, it appears that CR 269 may not actually be a true cluster.

4. Globular Clusters

NGC 4372 (12 25.8 -72 40) is a large well-resolved globular cluster with almost no central condensation. Many faint stars are visible and there is a 7th magnitude star on the northwestern edge. This globular is partially obscured by a long spindly dark nebula.

The second globular, NGC 4833 (12 59.6 -70 53), is somewhat brighter, being easily visible in my 80 mm finder. This one is somewhat more condensed but still easily resolved. There is a 9th magnitude star to the north.

5. Planetary Nebulae

Musca has a lot of planetaries and you could spend a long time hunting them all down. Most of the fainter ones are almost stellar so an OIII filter is almost essential. NGC 4071 (12 04.2 -67 18) is no pushover and is pretty difficult without the OIII filter. It is quite large (about 1'), essentially colourless and of pretty even surface brightness.

Sa 2-86 (12 30.5 -64 51.2) is one of the almost stellar ones at 3.6" and definitely needed the OIII. It is at the apex of an isosceles triangle formed with two slightly fainter stars. IC 4191 (13 08.8 -67 39) is again almost stellar at 5" but is brighter than the preceding and shows the typical blue colour of many planetaries.

NGC 5189 (13 33.5 -65 59) is the main attraction in Musca. I don't know any other planetary nebula this bright that looks so strange. Many people say that it resembles a barred spiral galaxy. The main part is an irregular bar containing much internal detail and pointing roughly WNW - ESE. There are irregular knots of nebulosity adjacent to the bar, seemingly stronger to the north. Two prominent stars are embedded in the nebulosity. The OIII filter assists greatly with this object.

The final planetary that I observed is MyCN 18 (13 39.6 -67 23), another one of the stellar variety that requires an OIII filter for certain identification.

6. Galaxies

Not much to report here. The brightest is IC 2980 (11 57.5 -73 41) was fairly easy to find as a faint elliptical blur elongated approximately NW-SE with prominent field stars at each end. Masochists with large telescopes may like to attempt a faint galaxy cluster on the southern edge of Musca, the brightest of which is magnitude 13.9 ESO 40-2 (13 10.3 -75 29.8). I wasn't successful but the conditions weren't perfect either.

Hope everyone enjoys this selection!

Searching for Planets with Infrared Spectroscopy

Len Williamson

Every month the Royal Society of Chemistry sends out a journal⁽¹⁾ that aims to keep members abreast of research and development in pure and applied chemistry. At the present time the emphasis is often medical science and the associated chemistry of drugs. Occasionally articles on astronomy appear which are informative and up-to-date in so far as this is possible at the present rate of expansion in this discipline A writing by Steve Miller⁽²⁾ in the November 2000 issue continues the tradition. Steve's article - illustrated in colour - was headed: H3+ A Space Odyssey.

Of particular interest to me was his account of the use of infrared (IR) spectroscopy. Those who have researched in chemistry will know of the immense value of this branch of spectroscopy. The thought occurred that CAS members might like to know of the work that could allow a direct observation of an exoplanet.

It will be known to all that an effect of the solar wind on Earth is to produce the aurora borealis. The solar wind is composed of ions and electrons (plasma) ejected by the Sun. Whilst the Earth's magnetic field deflects the wind (the magneto-pause is 60,000 km away from Earth) charged particles accelerate along the lines of magnetic force and enter the ionosphere at the poles to produce aurorae. Similar considerations apply to Saturn - most CAS members will have seen the Hubble Space Telescope photographs showing bright auroral ovals over the poles of Saturn.

The atmosphere of Jupiter has been studied for many years and we now know it is composed essentially of atoms and molecules of hydrogen and helium. In 1988 a French-American team led by Pierre Drossart of the Observatoire de Paris-Mendon were looking for the (weak) IR emission of the hydrogen molecule. They found one line of the spectrum at 2.122 microns, but also observed other nearby lines that were eventually identified by collaboration with the Herzberg Institute and University College in London as the overtone spectrum⁽³⁾ of the H3+ ion. The overtone spectra of most molecules are generally very weak, but for this molecular ion it was sufficiently strong to equal the H2 transition even though the latter was much more abundant. The more intense fundamental spectrum of this molecular ion is found around 3.7 microns and it was confirmed that H3+ was indeed present in the Jovian atmosphere - the highest concentration occurring at the poles. Subsequently they also found H3+ in the atmospheres of both Saturn and Uranus.

H3+ looks superficially like the symbol for an ion of the radioactive hydrogen isotope tritium (used by chemists as a labeler in reaction pathway studies) which is written as 3H+. Tritium is formed continuously in the upper atmosphere of Earth by cosmic ray induced reactions and presumably it could be detected on exoplanets with atmospheres like ours. An email from Steve advised that H3+ is in fact a molecule formed by the combination of a proton with a molecule of hydrogen. He writes in his article that this molecular ion plays a vital role in the reaction pathways that give rise to the molecules found in interstellar clouds in which stars are born. An astronomer at MSO confirmed this view.

The amount of H3+ in Jupiter's atmosphere is relatively high since its close-by volcanic satellite Io ejects 1 tonne per second of sulphurous material into space in the form of plasma. The intensely powerful magnetic field of Jupiter - 20,000 times greater than Earth's - sweeps the plasma into a vast sheet in the equatorial plane which rotates with the planet and from which ions race along the lines of magnetic force to plunge into the ionosphere at the poles. There they react with molecular hydrogen to form H3+ ions. For Saturn the source of plasma is from the solar wind only. Consequently the concentration of H3+ is one hundredth of that of Jupiter. Uranus with its axis in the plane of the ecliptic exhibits an almost uniform low concentration of the ions, the auroral enhancement being only 20% greater.

It was only as recent as October 1995 that Michel Mayor and Didier Queloz of the Geneva Observatory announced that a Jupiter-like planet orbited 51 Pegasi - a star of similar mass to our Sun. By the end of that month a separate team of astronomers in the U.S had confirmed the discovery. Yet in the April issue of the Southern Cross an edited version of a press release from the European Southern Observatory was published which stated that there were 63 known exoplanet candidates with minimum masses below 10 Jupiter masses, and 67 known objects with minimum masses below 17 Jupiter masses. The progress is spectacular!

The method used was to determine the changes in the radial velocity of the central star, these changes arising from the gravitational pull of unseen planets as they orbited the star. The velocity variations allow calculation of the planets' orbits and minimum masses, and when the HARPS high-resolution spectrograph is installed on the E.S.O. 3.6-m telescope at La Silla at the end of 2002 it will then be possible to detect planets down to ten Earth masses.

The wobble of a star can also be determined by positional measurements (astrometry), and it was in 1943 that two teams of astronomers in the U.S. announced that 61 Cygni and 70 Orphiuchi were orbited by planets at least ten times the size of Jupiter. The claim was subsequently not confirmed due to lack of precision in the measurements. However the E.S.O. press release says that when the Very Large Telescope Interferometer at Paranal becomes available, very high accuracy measurements will be possible.

Both the astrometric and spectrographic methods have the common aim of determining the wobble of a star to infer the presence of a planet. Could IR spectroscopy detect H3+ in the atmospheres of these giant Jupiter-like planets and for the first time make a direct observation of an exoplanet?

A planet orbiting HD98230 is at least 30 times heavier than Jupiter and orbits only 0.06 a.u.⁽⁴⁾ from the central star. Another exoplanet eight times heavier than Jupiter orbits tau Bootis even closer at 0.05 a.u. At the University College London a computer model of the upper atmosphere of Jupiter has been made which allows simulation of the chemical and dynamical conditions on Jupiter.

The model has been used to see what would happen to the H3+ level if Jupiter were moved to within 0.05 a.u. of the Sun. It turns out that it increases by a factor of 100,000 as the planet heats up and the levels of ionisation increase. One could expect that there would be some combination of the properties of the central star and an orbiting Jupiter-like planet that would maximize the formation of H3+ . Perhaps it will then be possible for some hardware in Earth orbit, or may be one of the state of the art giant telescopes, to detect those spectral lines!

If any CAS member is interested to read Steve Miller's article as published please advise and a copy will be sent.

(1) Chemistry in Britain, 36, Number 11, November 2000

(2) Steve Miller is a reader in science communication and planetary science at University College London

(3) Overtone spectra occur when a molecule is excited to the second vibrational level and relaxes to the ground state

(4) A.u: the distance from Earth to the Sun, approximately 150,000,000 km

The Galaxies of Sextans

Jenni Kay FRAS

Sextans is a constellation that does not stand out very well in my skies, nor is it made up of sufficiently bright stars to shape an easily recognisable form. Plus, in general it lies in a rather vacant area of sky with very few stars. However, having said that, it can still be found quite easily. First of all, it lies northeast of the very prominent Alpha Hydrae, and east-southeast of a gaggle of stars comprised of Delta, Epsilon, Zeta, Eta and Mu Hydrae. These more prominent stars make good signposts to locate the constellation of Sextans.

The stars that can easily be seen in Sextans are Alpha, Beta, Gamma, Delta, Epsilon and four others, ranging in brightness from 4.5 mag to 5.4 mag (for the five principal stars). Overall, I found that most of the galaxies I observed in Sextans were somewhat difficult, being extremely faint. In fact, there were a good many I could not detect at all at low power (105x), but could see them confidently at 150x. Even though many were a struggle, there were a couple of rather bright galaxies that were certainly worth the effort to track down.

The following observations were made from my semi-rural home site at Lobethal, SA, with a 12.5" f/5 Dobsonian. Typically, the skies here have a limiting naked eye magnitude of 6.1, with the seeing rated at ANT II-III.

NGC 2969 : 09 41.8 -08 37 (14.7v; 1.5' x 1.3'; surface brightness 15.3v; position angle 40 degrees.)

105x: Some doubt, there might be something there as a very faint, small, hazy smudge. 150x: Much improved view - very faint, relatively small, round, 40" in size, low surface brightness, very smooth glow throughout. Can be seen with full confidence, especially with averted vision.

NGC 2978 : 09 43.3 -09 45 (12.7v; 1.1' x 0.9'; sb 12.5v; pa 85d.)

105x: Too faint for me to detect. 150x: Much improved - obvious enough, especially with averted vision, very faint, small, round, hazy glow, 30" in size, with a low surface brightness. Can detect with full confidence at this power. N2980 lies nearby to the north.

NGC 2979 : 09 43.1 -10 23 (12.8v; 1.7' x 1.0'; sb 13.2v; pa 15d.)

105x: Too faint. 150x: Much improved - obvious enough, especially with averted vision, very faint, small, round glow, 30" in size, with a low surface brightness.

NGC 2980 : 09 43.2 -09 37 (13.0v; 1.6' x 0.9'; sb 13.2v; pa 160d.)

8.0' north of N2978. 105x: Obvious enough with care and averted vision - very faint, small, oval shaped glow. 10X: Improved - relatively bright, oval, 45" x 30"; major axis almost N-S, smooth and even glow throughout, with a high surface brightness.

NGC 3007 : 09 47.6 -06 26 (13.7v; 1.4' x 0.7'; sb 13.5v; pa 90d.)

105x: Too faint. 150x: Bit of a struggle and requires much care, attention, and averted vision - extremely faint, very small, round, hazy spot, 20" in size. Pops in and out of view in moments of steady seeing. There is a 13 mag. field star immediately to the south of the galaxy.

NGC 3018 : 09 49.7 +00 37 (13.3v; 1.2' x 0.9'; sb 13.3v; pa 27d.)

105x: too faint, possibly lost in the glare of a nearby 10 mag. field star. 150x: Care required - extremely faint, small, round, hazy spot, 30" in size, with a very low surface brightness. Seen as a soft glow on the southeastern side of the 10 mag. star. NGC 3023 lies immediately to the east.

NGC 3023 : 09 49.9 +00 37 (12.2v; 2.9' x 1.5'; sb 13.6v; pa 70d.)

2.3' east of N3018. 105x: suspected as an extremely faint, oval shaped, hazy glow. 150x: Much improved, especially with averted vision - very faint, round, 1.5' in size, very smooth and soft hazy glow.

NGC 3029 : 09 48.7 -08 03 (14.0v; 1.5' x 0.9'; sb 14.2v; pa 130d.)

105/150x: Too faint for me to detect.

NGC 3035 : 09 51.8 -06 49 (12.7v; 1.6' x 1.5'; sb 13.5v; pa 25d.)

105x: too faint. 150x: Much improved - very faint, small, round, hazy glow, 30" in size, with a low surface brightness. Can be detected with full confidence at this power, especially with care and averted vision.

NGC 3039 : 09 52.5 +02 09 (13.4v; 1.0' x 0.6'; sb 12.7v; pa 12d.)

105x: Too faint. 150x: Requires much care, attention and averted vision - extremely faint, very small, round, 25" in size, with a low surface brightness. There are four very faint 14/15 mag. stars in a bit of a group, and it is only with care that it can be realised that one of these stars is nonstellar, or more like a fat fuzzy star. This is the galaxy. But, a casual glance of the field would mistake the galaxy for just a star. NGC 3044 lies in the same, general field to the south-southeast.

NGC 3042 : 09 53.4 +00 42 (12.8v; 1.1' x 0.7'; sb 12.4v; pa 111d.)

105x: With care and attention, suspect there is a very faint, very small, round, hazy spot. Lies northeast of a 14 mag. star. 150x: Much improved - very faint, very small, round, 25" in size, with a low surface brightness. Averted vision holds with full confidence.

NGC 3044 : 09 53.7 +01 35 (11.9v; 4.3' x 0.8'; sb 13.1v; pa 13d.)

Almost 40.0' south-southeast of N3039. 105x: Obvious enough, especially with averted vision - relatively faint, long, slim, pencil like hazy wisp. There is a gradual brightening towards the centre. 150x: Improved - relatively bright, long, 4.0' x 30" in size, major axis is southeast to northwest, high surface brightness, and gradually brightens to the middle. This sight is worth the effort!

NGC 3047 : 09 54.6 -01 18 (13.2v; 0.5' x 0.5'; sb 11.5v.)

150x: Requires care, could be overlooked being mistaken for a faint star. Overall, the galaxy appears as faint, very small, almost stellar, round, 15" in size, with a very low surface brightness. Lies southeast of a bright 9 mag. field star.

NGC 3055 : 09 55.3 +04 16 (12.1v; 2.0' x 1.1'; sb 12.8v; pa 63d.)

105x: Obvious enough, especially with averted vision - relatively faint, relatively large, elongated southwest to northeast, hazy glow. 150x: Much improved - relatively bright, 2.0' x 40" in size, high surface brightness, smooth and even glow throughout, with a gradual brightening towards the centre.

Group of six galaxies : NGC 3083, N3086, N3090, N3092, N3093, and N3107

NGC 3083 : 09 59.9 -02 52 (13.7v; 1.2' x 0.4' sb 12.8v; pa 50d.)

150x: Requires much care, attention, and averted vision - exceedingly faint, very small, round - little oval in shape, 25" in size, very low surface brightness, with the major axis lying southwest - northeast.

NGC 3086 : 10 00.2 -02 58 (13.9v; 1.2' x 0.4'; sb 13.0v; pa 145d.)

7.7' southeast of N3083. 150x: Bit of a struggle, pops into view in moments of steady seeing - exceedingly faint, small, round, 25" in size, very low surface brightness. Requires much care, attention, patience and averted vision, and then, seen on several occasions for a confident observation.

NGC 3090 : 10 00.6 -02 57 (12.6v; 1.6' x 1.4'; sb 13.3v; pa 90d.)

4.5' east of N3086. 150x: Obvious enough - relatively bright, small, round hazy glow, 25" in size, with a high surface brightness. There are three 11 mag. field stars forming a triangle, and the galaxy lies near the western star. Overall, the galaxy was rather easy to pick out.

NGC 3092 : 10 00.9 -03 00 (13.3v; 1.3' x 0.7'; sb 13.0v; pa 30d.)

5.0' southeast of N3090. 150x: very tough, 90% confident the glow is real - exceedingly faint, very small, round, 25" in size. Seen with averted vision on several occasions.

NGC 3093 : 10 01.0 -02 57 (14.2v; 0.6' x 0.3'; sb 12.2v; pa 50d.)

2.6' northeast of N3092. 150x: Challenge, at first glance there seems to be only three faint stars here, but with care, it can be realised, that one of these "stars" is a little fat and fuzzy, nonstellar. This is the galaxy. Overall, it is very faint, very small, round, 10" in size.

NGC 3107 : 10 01.7 -02 59 (14.4v; 1.0' x 0.3'; sb 12.9v; pa 150d.)

10.5' east-southeast of N3093. 150x: Requires much care, attention, and averted vision - exceedingly faint, small, round, 25" in size, with a very low surface brightness. Seen on several occasions with averted vision for a confident observation.

NGC 3117 : 10 06.2 +02 54 (13.3v; 1.0' x 1.0'; sb 13.1v.)

105x: Too faint. 150x: Requires much care and attention - exceedingly faint, small, round, hazy spot, 25" in size. Seen with confidence and averted vision holds almost continuously.

Small group of four galaxies : NGC 3156, N3165, N3166, and N3169

NGC 3156 :10 12.7 +03 08 (12.3v; 1.8' x 1.1'; sb 12.9v; pa 47d.)

105x: Obvious - relatively bright, very small, round, hazy spot. Lies northwest of a triangle of three bright 8/9 mag. field stars. 150x: Much improved - relatively bright, oval, 40" x 30" in size, major axis is southwest to northeast, high surface brightness, smooth and even glow throughout, with a slight brightening to a small, round, central core.

NGC 3165 : 10 13.5 +03 23 (13.9v; 1.5' x 0.7'; sb 13.8v; pa 177d.)

19.3' northeast of N3156. 150x: At the limit of detection - exceedingly faint, small, round, 20" in size.

NGC 3166 : 10 13.8 +03 26 (10.4v; 1.6' x 2.6'; sb 12.9v; pa 87d.)

4.3' northeast of N3165. 105x: A visual treat, a twin pair with N3169. Obvious - bright, small, round, hint of a soft outer halo. 150x: Much improved - bright, relatively small, round, 40" in size, high surface brightness, with a brighter core, 25" in size. In the general view, there is a scatter of a few stars, a smooth dark background sky, and the two obvious galaxy glows. 10/10 for this view.

NGC 3169 : 10 14.2 +03 28 (10.2v; 5.0' x 2.8'; sb 12.9v; pa 45d.)

7.6' east-northeast of N3166. 105x: Obvious - bright, small, round, hazy glow with a hint of a soft outer halo. 150x: Much improved - bright, round, relatively small, 40" in size, with a high surface brightness and a brighter core region 20" in size.

Deep Sky Observing with the Webb Society

Jenni Kay FRAS

For those wishing to expand their deep sky observing activities, you may want to consider joining the Webb Society. The Webb Society was established in 1967 in the UK and is a forum for deep sky enthusiasts all over the world. It provides a single platform for both the professional and amateur astronomer to share their interests. The information on offer is extensive and wide-ranging, from deep sky observing reports to the measurements of double stars, from reviews of the latest books and software to current techniques in stellar photometry. There is everything here to inform the reader, regardless of their special interest.

Members receive a quarterly journal called the Deep Sky Observer. In here one will always find a variety of article topics submitted by members. For example, in issue # 119 the list of articles include: "NGC 1360 in Fornax" by Lee McDonald, "Some Faint Galaxies for the Autumn and Winter" by Jan Sandstrom, "Software & Data for Practical Astronomers" by David Ratledge, "CCD Images" by David Briggs et al, - just to name a few.

There is also an ever growing list of handbooks available to members. These include such titles as : Double Stars; Planetary & Gaseous Nebulae; Open and Globular Clusters; Galaxies; Clusters of Galaxies; Anonymous Galaxies; The Southern Sky; Variable Stars; and An Introduction to Visual Deep-Sky Observing. Furthermore, there will soon be a new handbook released on visual observations of clusters and nebulae in the Magellanic Clouds.

Members can be kept up to date with the very latest in news and events over the Internet through the Webb Society email list. This forum brings the professional and amateur much closer together, allowing a quick flow of information and data not usually readily available by other means.

If you would like more information on the Webb Society, or details on how to join, please do not hesitate to contact me at:

jenni@senet.com.au; or by ordinary post at:

Jenni Kay
Secretary of the Southern Skies for the Webb Society
PO Box 74
Lobethal, SA. 5241

You can also find information on the web at:

www.webbsociety.freeserve.co.uk

As the secretary of the southern skies, I would always be available to offer advice and assistance to ensure you can get the most enjoyment from this hobby.