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IC 1805: The Heart Nebula in HDR

IC1805.jpg
Credit & Copyright: Daniel Verloop (Beursacademie)

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Emission nebula IC 1805

IC1805_Center_FC_43.jpg

The Heart Nebula, IC 1805, Sh2-190, lies some 7500 light years away from Earth and is located in the Perseus arm of the Galaxy in the constellation Cassiopeia. This is an emission nebula showing glowing gas and darker dust lanes. The nebula is formed by plasma of ionised hydrogen and free electrons.
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Heart and Soul nebulae
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NASA's Wide-field Infrared Survey Explorer, or WISE, has captured a huge mosaic of two bubbling clouds in space, known as the Heart and Soul nebulae. The space telescope, which has completed about three-fourths of its infrared survey of the entire sky, has already captured nearly one million frames like the ones making up this newly released mosaic.
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The Heart Nebula, IC1805
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IC1805
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Early stars in IC1805
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Title: Early-type stars in the young open cluster IC1805. II. The probably single stars HD15570 and HD15629, and the massive binary/triple system HD15558
Authors: M. De Becker, G. Rauw, J. Manfroid, P. Eenens

Aims: We address the issue of the multiplicity of the three brightest early-type stars of the young open cluster IC1805, namely HD15570, HD15629 and HD15558.
Methods: For the three stars, we measured the radial velocity by fitting Gaussian curves to line profiles in the optical domain. In the case of the massive binary HD15558, we also used a spectral disentangling method to separate the spectra of the primary and of the secondary in order to derive the radial velocities of the two components. These measurements were used to compute orbital solutions for HD15558.
Results: For HD15570 and HD15629, the radial velocities do not present any significant trend attributable to a binary motion on time scales of a few days, nor from one year to the next. In the case of HD15558 we obtained an improved SB1 orbital solution with a period of about 442 days, and we report for the first time on the detection of the spectral signature of its secondary star. We derive spectral types O5.5III(f) and O7V for the primary and the secondary of HD15558. We tentatively compute a first SB2 orbital solution although the radial velocities from the secondary star should be considered with caution. The mass ratio is rather high, i.e. about 3, and leads to very extreme minimum masses, in particular for the primary object. Minimum masses of the order of 150 50 and 50 15 solar masses are found respectively for the primary and the secondary.
Conclusions: We propose that HD15558 could be a triple system. This scenario could help to reconcile the very large minimum mass derived for the primary object with its spectral type. In addition, considering new and previously published results, we find that the binary frequency among O-stars in IC1805 has a lower limit of 20%, and that previously published values (80%) are probably overestimated.

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Cassiopeia W3
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Astronomers announced today that they have found a nebula. Known as W3, this glowing gas cloud 7000 light-years away in the constellation Cassiopeia has just begun to shine with newborn stars. Shrouds of dust currently hide its light, but this is only a temporary state. In 100,000 years - a blink of the eye in astronomical terms - it may blaze forth, delighting stargazers around the world and becoming the Grand Nebula in Cassiopeia..

"The Grand Nebula in Cassiopeia will appear in our sky just as the Great Nebula in Orion fades away. Even better, its home constellation is visible year-round from much of the northern hemisphere" - Tom Megeath, Smithsonian astronomer (Harvard-Smithsonian Centre for Astrophysics), who made the announcement in a press conference at the 207th meeting of the American Astronomical Society.

The Orion Nebula is one of the most famous and easily viewed deep-sky sights. It holds special significance for researchers as the nearest region of massive star formation.
The star formation process begins in a dark cloud of cold gas, where small lumps of material begin to contract. Gravity draws the gas into hot condensations that ignite and become stars. The most massive stars produce hot winds and intense light that blast away the surrounding cloud. But during the process of destruction, stellar radiation lights up the cloud, creating a bright nebula for stargazers to admire.

"Orion may seem very peaceful on a cold winter night, but in reality it holds very massive, luminous stars that are destroying the dusty gas cloud from which they formed. Eventually, the cloud of material will disperse and the Orion Nebula will fade from our sky" - Tom Megeath.


Position (2000): RA: 3h01m56s Dec: +60d35m50s
This artist's depiction simulates the view that amateur astronomers on Earth might enjoy 100,000 years from now, when the Grand Nebula in Cassiopeia lights up.
Credit: David A. Aguilar


Of special interest to Megeath is a system of four bright, massive stars at the centre of Orion known as the Trapezium. These stars bathe the entire nebula with powerful ultraviolet radiation, lighting up nearby gas. Even a modest telescope reveals the Trapezium surrounded by billowing ripples of matter gleaming eerily across the vastness of space. Yet the Trapezium is only the tip of the iceberg, surrounded by more than 1000 faint, low-mass stars similar to the Sun.

"The question we want to answer is: why are these massive stars sitting in the centre of the cluster?" - Tom Megeath.

There are two competing theories to explain the Trapezium's location. One holds that the Trapezium stars formed apart from each other but descended to the centre of the cluster, ejecting a spray of low-mass stars in the process. The other leading theory is that the Trapezium stars formed together in the centre of the cluster and have not moved from their birthplace.

"Obviously, we can't go back in time and look at the Trapezium when it was still forming, so we try to find younger examples in the sky" - Tom Megeath.

W5 is also known as IC1848 and together with IC1805 it is part of a complex region popularly dubbed the Heart and Soul Nebulae.
Such proto-Trapeziums would still be buried in their birth cocoons, hidden to visible-light telescopes but detectable by radio and infrared telescopes. Searches at those longer wavelengths have identified many regions where massive stars are forming, but could not determine whether the protostars were alone or in collections of four or more stars that could be considered Trapeziums.
Megeath and his colleagues examined one such protostellar clump in W3 using the NICMOS instrument on the Hubble Space Telescope and the National Science Foundation's Very Large Array. They discovered that the object, which was thought to be a binary star, actually contained four or five young, massive protostars, making it a likely proto-Trapezium.
These protostars are so young that they appear to be still growing by accreting gas from the surrounding cloud. All of the stars crowd into a small area only about 500 billion miles across (just under one-tenth of a light-year), making this cluster more than 100,000 times denser than stars in the Sun's neighbourhood. This suggests that the massive stars in Orion's Trapezium formed together in the centre of the cluster.
The same physical processes that have carved the Orion Nebula now are moulding the W3 nebula. The massive stars in this compact group are starting to eat away at the surrounding gas with ultraviolet radiation and fast stellar outflows. Eventually, they will destroy their dense cocoon and emerge to form a new Trapezium in the centre of W3. However, the final form of the nebula and the time that it will reach maximum brilliance are uncertain.

"Who knows, in 100,000 years the emerging Grand Nebula in Cassiopeia may replace the fading Orion Nebula as a favourite object for amateur astronomers. In the meantime, I think it will be a favourite target for professional astronomers trying to solve the riddle of massive star formation" - Tom Megeath.

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IC1805
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This image of two bright emission nebulas nicknamed Heart and Soul can be found in the constellation Cassiopeia. The Heart Nebula, officially dubbed IC 1805 (on the right), has a shape reminiscent of a classical heart symbol.


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Both nebulas, are shown in false colour, shine brightly in the light of energised hydrogen. Several young open clusters of stars populate the image and are visible in and around the nebula centres. The nebulas are located about 6,000 light years away and together span roughly 300 light years.

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