Indus

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The constellation of Indus was originally created by Petrus Plancius from the observations of Dutch sea navigators Pieter Dirkszoon Keyser and Frederick de Houtman when exploring the southern hemisphere. Indus’ stellar patterns became known when it appeared on a celestial globe in 1597 and was considered a constellation when it was added to Johann Bayer’s Uranometria catalog in 1603. It survived the years to become one of the 88 modern constellations recognized by the International Astronomical Union. Indus is located south of the ecliptic plane and covers approximately 294 square degrees of sky. It consists of three main stars in the primary asterism and has 16 stars with Bayer/Flamsteed designations. Indus is bordered by the constellations of Microscopium, Sagittarius, Telescopium, Pavo, Octans, Tucana and Grus.

Since the constellation of Indus wasn’t created until late in the sixteenth century, there isn’t any ancient mythology associated with its stellar patterns. However, Indus is meant to represent as a native – perhaps one met by the Dutch explorers on their travels in the Indies or Africa. It is also believed that Johannes Bayer wish to honor the native American Indians as well, so Indus was thus included in his works.

For observers, let us begin with binoculars the brightest star – Alpha Indi – the “a” symbol on our map. Who know exactly how stars sometimes get their names, but you’ll often find this star is called ” the Persian” on some lists. Located about 101 light years from our solar system, Alpha is super-metal-rich, K-type orange giant star that outshines our own Sun by about 62 times. Have a telescope? Be sure to take a look at “the Persian”. You’ll find it has a pair of 12th and 13th magnitude red dwarf star companions!

Now hop to the center of this Y-shaped asterism and have a look at Theta Indi. That’s right! Another binary star. Located about 91 light years from Earth, you’ll find a very nice double star here, with components that are easy to separate with a small telescopes. The primary is fifth magnitude and the secondary is magnitude seven.

Time to follow the branch of the Y southwest and have a look at Beta Indi – the “B” shape on our map. While the rest of the stars we’ve look at so far were fairly near – Beta isn’t. Located at minimum of 600 light years away, Beta Indi is a very massive and luminous star of the orange K-type classification. Take a look through the telescope, too… Because you’ll find that Beta also has a 12th magnitude visual companion whose distance is unclear. At the southeast end of the Y branch is Delta, whose orbital mechanics have been closely studied.

Now drop south for Epsilon – the backward “3”. Epsilon Indi is one of the closest stars to Earth, approximately 11.82 light years away. Epsilon is a dwarf star – only about 75% the size of our own Sun – and very similar in respects to movement, corona and gravity. Even its photosphere and metallicity is a close comparison. In 1847, Heinrich Louis d’Arrest was the first to notice that Epsilon had moved right along compared to its charted 1750 position, and it has been measured about every 100 years since. Astronomers have since placed it in what is called the Epsilon Indi Moving Group of Stars – a stellar association of about 16 members that quite likely formed about the same time in the same location.

Of course, being so close means Epsilon was also the object of many signal studies, including radio signals and lasers – but unfortunately, no signals were ever returned. Even though we haven’t gotten a reply, it still leads the list of 17,129 nearby stars most likely to have planets that could support complex life. With good reason! In January 2003, astronomers announced the discovery of a brown dwarf with a mass of 40 to 60 Jupiter masses in orbit around Epsilon Indi at a distance of at least 1500 astronomical units… And what’s more, it’s actually a binary brown dwarf star! Although measurements of the radial velocity of Epsilon Indi appear to show the presence of a planetary companion with an orbital period of more than 20 years, so far no space telescope yet has been able to prove its existence.

Now it’s time to take a telescope tour of Indus. Our first object is IC 5152 (RA 22:02.9 Dec -51:17). Hanging out about 3 million light years away, this irregular dwarf galaxy could very well be an outlying member of our own Milky Way local group of galaxies. At roughly magnitude 11, look for some patchy details, including a line of sight star caught on its edge.

Next up? NGC 7090 (RA 21:36.5 Dec -54:33). Even though billed at near magnitude 11, this soft spoken spiral galaxy is low surface brightest to the eye – but an astrophotographer’s dream. It has a fantastic h-alpha halo! Look for several scattered stars in the same field, including a very wide equal optical pair lying to the east.

Hop now to NGC 7083 (RA 21:35.7 Dec -63:54). At magnitude 12, this galaxy is meant for larger telescopes, but this barred galaxy is also highly studied for its spiral galaxy structure. It is considered a grand design and well worth taking some time on!

Last for now? NGC 7049 (RA 21:19.0 Dec -48:34). Although on the small side, NGC 7049 is a bit brighter than our last study at magnitude 11. It is an early-type spiral galaxy and also a target of the Hubble Space telescope, which studied it for its inner polar disc properties. You’ll find it about about 15′ east of a bright, yellowish star (6.5 magnitude) and the surface brightness will allow you to do a little more serious studying!

Source: Wikipedia, ESO
Chart courtesy of Your Sky.