Object of the Week, February 21, 2021 - VY Canis Majoris Nebula

VY Canis Majoris nebula
R.A.: 07 22 58.3
Dec.: -25 46 03 (2000)
Type: Reflection
Size: ~10"
Central star: mag 7.4-9.6

The VY CMa nebula was mentioned by Sandor Szabo (with his sketch) on DeepSkyForum in May 2016, but I thought this unique star and nebula was worthy of an OOTW

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VY CMa is a remarkable stellar behemoth -- red hypergiant variable star and a powerful infrared source. Although its diameter and luminosity are difficult to pin down precisely, it is certainly one of the largest and intrinsically brightest stars in the Milky Way. The measurement of size is dependent on wavelength, but it extends ~2,000 times the solar diameter with a total bolometric luminosity of 400,000 times or more the Sun's luminosity (though mostly in the infrared).

Episodic extremely high mass-loss ejections - 30 times the mass of the earth/yr - have enshrouded VY CMa in a small, irregular reflection nebula of a gas and dust with a small tail or jet shaped like the Nike Swoosh logo! Interestingly, beginning in 1897 double star observers reported seeing individual companions to VY CMa. These components varied in brightness quite over the years and are now considered to be nebulous condensations (stellar "knots") in the tail.

In 1923, Charles Perrine, director of the Cordoba Observatory in Argentina, reported that observer Senor Guerin discovered a nebula surrounding VY CMa with the 7.5" meridian circle at the observatory.

"Senor Guerin described the object as a nebula about 8" x 12", red, tending toward dark red or scarlet; as containing three nuclei, the preceding of which is the brightest and the point which he observed for position. The general aspect is that of a comet, the tail (which is excessively faint) extending to the [west] (Power 220). With a power of 500 the tail is seen prolonged in a sinuous form to the south..."

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Using the 100-inch at Mt. Wilson many years ago, astronomer David Allen reported "The nebula is very easy and appears to be extended mostly to the W. The star is extremely red; several of the star-like knots are visible."

Here are three of my observations (unfiltered) --

17.5-inch: VY CMa is a striking orange-red color. At 175x it appeared slightly fuzzy or soft, like a brighter star that wouldn't focus. At 285x unfiltered, a very small non-stellar orange disc was clearly visible surrounding a brighter center. More surprisingly a short "tail" clearly extended from the glow to the west. At 325x, the central star was cleanly resolved within a very small, 4" round halo. The nebulous tail or filament curved slightly ~8" to the WNW.

24-inch: at 125x, VY CMa stands out in the field as bright orange-red star. At 375x, VY CMa had a soft appearance (extending a few arc seconds) with a short, nebulous tail extended less than 10" to the west.

48-inch: VY CMa appeared as a mag 8 orange star with a bright, high surface brightness curving jet extending to the west. I was startled by the contrast between the color of the blue jet and the color of the star. The jet bent outwards slightly towards the north.

The mass loss and dust distribution in this nebula was mapped by Keck and HST using polarized light at different wavelengths and colorized in this image --

Attachment 4214

As always,

"Give it a go and let us know!
Good luck and great viewing!"

This was published today: https://www.nasa.gov/feature/goddard...-stars-dimming

Fascinating! I wonder how this is impacting the visual nebula (tail). I haven’t taken a look in a few years.

Thanks Steve, this OOTW post motivated me to observe VY CMa - I don't remember hearing of it before. I was fortunate to have a three excellent observing nights in Central Oregon last week, and on the third night the seeing settled down and I was able to see both the disk around VY and its nebula:

" Well now, this is interesting! The seeing is much steadier than last night - no wind either - and even though the image is undulating it's clear enough to see some detail... The star sits in the middle of a small, slightly dimmer disc. Can't say it looks nebulous - it's a distinct disc - and the tail shoots out from the disc westward. All this is enveloped in a circular glow, which doesn't look like irradiation compared to close by stars of similar brightness. So very cool! VY and its disc are a lovely orange-yellow. 408x, 547x, 21.97 SQM.

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This isn't the best sketch ever, but I think it gives the idea of what I saw as well as a taste of the undulating seeing. Any discrete lines are artifacts of the tiny size of my sketch, and remind me I should have drawn VY at a larger scale.

Also, seeing the winter sky tilting toward the west as it got dark, a very bright Zodiacal Light, and seeing them both reflected in a nearby lake was breathtakingly beautiful. I literally gasped when I stepped out of my van!

Nice observation, Howard. I was also curious on the current appearance and took another look in my 24" two weeks ago. As you reported the bright orangey star is definitely surrounded by a small halo. I thought the tail to the west was a bit broader and less distinctly defined as 8 years ago (last observation). Could have been seeing conditions, though, which were just average.

Very cool object Steve. Despite the low Declination I could detect (27", 488x, Seeing II, NELM 6m5+) a halo ranging from southwest to north with a better defined "arm" to the northwest. I will add the sketch later.

I finally completed my sketch Steve. What a cool "star".

sketch: 27", 488x, NELM 6m5+, Seeing II
Attachment 4300
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AWESOME! I did not know about this and since I now have a 16" f/4.5, I really think I should be able to see it!! By the way, it was nice of Steve to leave a link to a former post where in that one he mentioned his 2012 S&T article. I had somehow overlooked that article, so I just dug it out and now want to also try for the nebulae around Z CMa!!! If only Canis Major wasn't going down in the west this time of year...

Scott