APOD: Sharpless 249 and the Jellyfish Nebula (2017 Jan 07)

[APOD Robot]

Sharpless 249 and the Jellyfish Nebula

Explanation: Normally faint and elusive, the Jellyfish Nebula is caught in this alluring telescopic mosaic. The scene is anchored below by bright star Eta Geminorum, at the foot of the celestial twin, while the Jellyfish Nebula is the brighter arcing ridge of emission with tentacles dangling below and left of center. In fact, the cosmic jellyfish is part of bubble-shaped supernova remnant IC 443, the expanding debris cloud from a massive star that exploded. Light from the explosion first reached planet Earth over 30,000 years ago. Like its cousin in astrophysical waters the Crab Nebula supernova remnant, the Jellyfish Nebula is known to harbor a neutron star, the remnant of the collapsed stellar core. An emission nebula cataloged as Sharpless 249 fills the field at the upper right. The Jellyfish Nebula is about 5,000 light-years away. At that distance, this narrowband composite image presented in the Hubble Palette would be about 300 light-years across.

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[Case]

Light from the explosion first reached planet Earth over 30,000 years ago.

This number seems to come from this paper:
Roger A. Chevalier sets out in “Supernova Remnants in Molecular Clouds” (1999) that
The radiative shell model provides an adequate description of the observations of shell A. The model implies an age t≈0.3R/v_s = 30,000 yr for r=7.4 pc and v_s = 100 km s⁻¹. This age is greater than some other estimates based on X-ray observations.

The wikipedia writers on IC 443 then say that
the progenitor supernova happened between 3,000[3] and 30,000[5] years ago.

[Chris Peterson]

Light from the explosion first reached planet Earth over 30,000 years ago.

This number seems to come from this paper:
Roger A. Chevalier sets out in “Supernova Remnants in Molecular Clouds” (1999) that
The radiative shell model provides an adequate description of the observations of shell A. The model implies an age t≈0.3R/v_s = 30,000 yr for r=7.4 pc and v_s = 100 km s⁻¹. This age is greater than some other estimates based on X-ray observations.

The wikipedia writers on IC 443 then say that
the progenitor supernova happened between 3,000[3] and 30,000[5] years ago.

Looking at some much more recent papers, it doesn't look like the situation has changed. Most of the work with modeling the morphology and the nature of the shock front emissions seems to simply assume an age of 10,000 years, typical for "middle-aged supernova remnants". One more recent work suggest an age based on the ejecta ring location of 4000 years. Others reference the range given by Wikipedia- 3-4 kyr and 20-30 kyr. I didn't find any recent papers that utilized more modern modeling techniques in an effort to come up with a more precise age.

Apparently, the distance has never been measured directly by any technique. The 5000 ly distance is based on the assumption that the remnant is part of the GEM OB1 association (a collection of stars and molecular clouds).

[neufer]

[img3="μ Gem & (Castor's "forward foot") Propus η Gem"]https://upload.wikimedia.org/wikipedia/ ... 3_wide.jpg[/img3]

<<Eta Geminorum (η Geminorum, abbreviated Eta Gem, η Gem), lies at the foot of the Castor side of Gemini (the mortal son of Tyndareus, the king of Sparta). η Geminorum is a triple system around 380 light years from the Sun. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) designated Propus (from the Greek, meaning forward foot) for this star. η Geminorum is near the ecliptic, so it can be occulted by the Moon and, very rarely, by planets. The last occultation by a planet took place on July 27, 1910, by Venus, and the next to last on July 11, 1837, by Mercury.

In 1865, Julius Schmidt first reported that η Geminorum was a variable star. The light variations were described as having long maxima of constant brightness, minima of greatly varying size and shape, and a period around 231 days. Such semi-regular variations are considered to be very similar to Mira variables, but with smaller amplitudes.

In 1881, Burnham observed that η Geminorum had a close companion. At that time the separation was measured to be 1.08". This has now increased to 1.65" and an orbit has been calculated to be 474 years long and rather eccentric. Little is known about the companion, although it is 6th magnitude. It is given a G0 spectral type and is assumed to be a giant on the basis of its brightness.

In 1902, William Wallace Campbell reported that η Geminorum showed radial velocity variations. The assumption was that the star was a spectroscopic binary, although no period or other orbital parameters were determined. An orbit calculated in 1944 is essentially unchanged today, with a period of 2,983 days and an eccentricity of 0.53. Observations were made looking for sign of eclipses corresponding to the derived orbit, but the evidence was regarded as inconclusive.>>

[ta152h0]

is there a Sharpless 248 ?

[Chris Peterson]

is there a Sharpless 248 ?

Sharpless 248 is IC 443. That is, this image shows Sh2-248 in the lower left, and Sh2-249 in the upper right.