Saturday, February 14, 2015

planetary nebula IC 418: a blue gem in a red cocoon

here's my first light with a new ccd camera: starlight xpress trius 694
believe it or not i've never used a filter wheel before
just manually screwed one filter on, imaged for a few nights, then went on to the next
not a big deal for super long narrow band imaging, but inconvenient for quick bright planetaries
so the filter wheel that came with the camera is more of a novelty to me
than the larger, more sensitive chip
thus a quick shot of a bright planetary as first light.

after seeing IC 418 listed as one of winter's best planataries in feb S&T
i decided to revisit the red planetary with narrow band filters
as my prior rgb effort yielded nothing but a red disk with a brighter spot in the center

so here it is in NII/OIII/OIII:



it's difficult to make out the central structure at native image scale
so i upsampled x2
for a final resolution of (EDIT: 0.2"/px)  (makes a difference to my eye)
straight linear stretch with a bit of RL deconvolution

in OIII there is a disk with a subtle central brightening:


here's the NII which shows a central star with an outer shell:


blink


difficult to say whether the mottling is noise or a hint of the spirograph pattern detected in the hubble image

interestingly combining the NII and OIII in a color image
seems to create an unsharp mask like effect
making the central OIII brightening (gem) more evident


prior effort (RGB 2007):


i also shot HeII subs but found only a very faint ring around the central star
seemed matched continuum filter images with equivalent exposure (accounting for bandwidth)
meaning it's either broadband glow or artifact such as reflections, corrector plate dust etc.

of course after imaging it i came across this on Jim Kaler's web site
indicating there are no HeII emissions:

http://stars.astro.illinois.edu/sow/ic418.html
"The low excitation nebula, with its relatively cool central star, does not exhibit He II emission lines (those of ionized helium), just those of He I (neutral helium)"
i believe this is taken from a 50 year old reference:
From L.H. Aller and J.B. Kaler, Astrophysical Journal vol. 140, p. 936, 1964.
so i'm a bit behind the times...

i also shot a 20 minute sub binned x2 in NII and OIII
and found no evidence of any other outer shell (didn't check Ha)


8" LX200R, SX Trius 694  0.4"/px
astrodon 3nm NII, 3nm OIII filters
NII 22x30s, OIII 20x30s
ASA DDM60
no AO no guiding
1/2/15

Thursday, February 12, 2015

Comet Lovejoy C/2014 Q2

caught a bright comet with an impressive tail in January:

The image frame is approximately 2 degrees wide, making this the longest comet tail I've captured as it clearly departs the frame.  Some images from dark skies show a tail spanning 19 degrees.  
This was shot through heavy light pollution and passing clouds (explaining the gaps in the star trails).  Nevertheless, the bright, twin tail structure is still visible.  
The comet was easily visible in binoculars, brighter than the andromeda galaxy, though i could not detect the tail.  
Here's a video of the individual frames complete with clouds and airplanes:
Note the comet tail follows the direction of the solar wind rather than the comet motion in this instance.   
Though fading a bit from peak brightness
It should still be visible early evening  in Andromeda this weekend with the new moon approaching

FS60C@ f/42. with SX H9C color camera and chroma light pollution filter.  60x2 minute exposures with mount tracking on comet (ASA DDM 60).  

Sunday, January 4, 2015

speaking of gas giants...Uranus

Uranus, seventh planet from the Sun. It has the third-largest radius and fourth-largest mass in the Solar System. Uranus is similar in composition to Neptune.  Along with Neptune, sometimes called an "ice giant" (prior post).  It has the coldest planetary atmosphere in the Solar System, with a minimum temperature −224 °C.  It has a complex, layered cloud structure, with water thought to make up the lowest clouds, and methane the uppermost layer of clouds.  At 20 a.u. it has an 84 year orbit.  Like other gas giants it spins rapidly, making one revolution in 17 hours.
Uranus has an axial tilt of 98°, so its axis of rotation is approximately parallel with the plane of the Solar System. This gives it bizarre seasonal changes. Combine this extreme tilt with it's 84 year orbit and you get a 21 year "night" at the pole during winter, compared to a 17 hour day at the equator during equinox.  
Like Neptune, there's not much to see visually.  Unlike Neptune, it can be seen with the unaided eye in dark locations.  At high power it can be seen as a small disk rather than a dot.  A slightly more green than Neptune.  A monster telescope or camera might detect several moons (see below), and possibly faint cloud formations.



The Hubble or flyby space craft can detect faint rings.

Saturday, January 3, 2015

Neptune overview

Neptune--eighth and farthest planet from the Sun (after Pluto’s demotion).  Along with Jupiter, Saturn and Uranus, a gas giant.  Smaller, but slightly more massive than its near-twin Uranus.  Uranus and Neptune are sometimes referred to as "ice giants" as they contain a higher proportion of "ices" such as water, ammonia, and methane.   Traces of methane in the outer atmosphere account for the planet's blue appearance.  At 30 au its orbit around the sun takes 165 years, so it’s not moving much in the sky from year to year. 
Discovered in 1846, Neptune was the first planet found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus suggested gravitational perturbation by another planet. There’s been controversy over credit for the discovery:
Interestingly, Galileo made the first recorded observation of Neptune, but apparently did not recognize it as a planet, though some have suggested that he was aware that it had moved relative to fixed stars. 

For visual astronomers, there’s not much to see except for the fact that at high power it can be seen as a small bluish disk rather than a dot.  It generally cannot be seen with the unaided eye.  Due to its distance, its apparent size is the smallest of the planets.  With dark skies or a camera you may be able to pick up a few moons.

Here’s an image of Neptune, the white spot to the right is its large moon triton:




With the Hubble or flyby space craft, surface storms and very faint rings have been detected.  

Monday, December 22, 2014

wiffed on einstein's cross: happy solstice

Gravitational lensing is a phenomenon predicted by einstein's general theory of relativity wherein the warp in space due to the gravitational field of a large galaxy or group of galaxies causes a magnification or lensing effect upon light from a galaxy that is more distant.  
einstein's cross a/k/a cgcg378-15 is a galaxy who's lensing effect splits the image of a distant background quasar into four separate images.  

i've been trying to image this elusive structure for years.  failing time and time again to even find it.  last year, i thought i'd caught it, but entered the incorrect catalog number, imaging the wrong galaxy (cgcg 378-14 instead of cgcg 378-15):



this year i'm sure i actually caught the right galaxy:



though the core doesn't look quite round, i certainly can't claim to have resolved the cross.  There do appear to be interesting reddish Ha emissions in the spiral arms.  
this one stays on the list for next year.

PS what i should see is 4 dots in the center instead of one. the dots represent the single distant quasar viewed through the distorted lens of the galaxy's gravitational field.
Here's a shot from a professional observatory with a an aperture measured in meters:

here's the Hubble super close up of the core only

with a little imagination, a close look at the core suggests it's not quite round, but not convincing enough to say i'm seeing the lensing effect.


happy solstice xmas and hanukka

details:
8" LX200R, SX AO, SX H9/H9C, .6"/px
IDAS LPR filter
lum 113x5 min, RGB 13x20 min
9/2014
Newport Beach, CA

Thursday, November 27, 2014

North America and Pelican Nebulae

North America and Pelican Nebulae

The North America Nebula is a huge emission nebula in Cygnus close to the bright star Deneb.
It took me years to see it through a telescope, even from dark skies.  At 4 times the size of the full moon, i was staring right at the middle of it with my long focal length telescope.  Finally i used a filter in the small low power finder scope on top and caught it.
This image is a two frame mosaic with my shortest focal length telescope, showing the North American nebula to the left, and the pelican nebula to the right of a central patch of dust.
This image uses the "hubble pallet" with high energy oxygen as blue, low energy sulfur as red, and hydrogen as green.



not entirely happy with the framing as i've clipped the west coast in order to include the pelican :(
might try again next year

Here it is with an alternative pallet using only high energy oxygen as blue and low energy sulfur as red (hydrogen was used in part as luminance):



Here's an older close up of the "cygnus wall" aka "gulf of mexico"



and the Pelican



Takahashi FS60c @255mm CS 8.6nm Ha, AD 3nm OIII, AD 3nm SII, SX H9
2 frame mosaic total time Ha 49x5 min, OIII 74x10 min, SII 92x10 min
Newport Beach, CA 10/2014

Sunday, November 16, 2014

Photographic Light Pollution Filter Comparison: Hutech IDAS LPS-P2 vs Chroma Loglow

Having recently moved I've noticed some improvement in my skies from bortle white to bortle "off white".  At zenith on a good night, my sky quality meter reads 18.12 mag/arcsec^2.  There is a red glow to the north up to an altitude of 40 degrees and a grey glow above that to 70 degrees.  The sky is darker above and to the south.   The milky way is impossible naked eye.
I do all my imaging from these skies with an LPS filter, narrow band filter, a combination of both.  Emission nebulae are great, galaxies are difficult, but can be very rewarding (especially if there are HII regions),  reflection nebulae are very difficult and dust is impossible.
As a testament to the fact that I purchase too many filters, I was given a Chroma Loglow filter to test.  So I've compared it the the Hutech IDAS LPS-P2 filter which many (including me) consider the gold standard light pollution filter.  A quick visual inspection showed more light passing through the Chroma than the IDAS.  I initially thought the Chroma had more of a reddish cast, but realized this was on a fluorescent bulb.  Searching around for an incandescent bulb yielded similar, more neutral color balance for each with perhaps a slight blue cast to the IDAS.

Iris Nebula, a reflection nebula surrounded by dust shot through heavy light pollution:
Reflection nebulae are usually blue because the scattering is more efficient for blue light than red (this is the same scattering process that gives us blue skies and red sunsets) (Wikipedia).
The black void above, below, right, and left of the nebula is caused by intervening dust.  darker skies allow the glowing dust to be imaged.

Dumbbell Nebula, an emission (planetary) nebula, at maximum elevation with minimal gradients due to light pollution:


Here are the details of the filter test:
It should be noted that the filters were used on different nights, though the conditions were similar.  My first target was M24, low in the south, but in the direction with least light pollution, using an FS 60C at F 4.2 and a Starlight Xpress H9C camera.  The star and background signal was much higher with the Loglow, though I did not note any difference in depth or gradients in this dense star field (comparison images not shown).  The seeing was slightly better when the IDAS was used.  The combined image can be seen here in a prior post.

Dumbbell Nebula
Next up was M27, an excellent target, as it has strong OIII and Ha emissions transiting at zenith in an area where gradients and light pollution are minimized.  Using an FS 102 at F 6, I compared a Baader IR/UV filter to the IDAS and the Loglow.  There were no appreciable light pollution gradients.  The nebular emission signal was enhanced relative to the stars with both the IDAS and the Loglow.  I could not appreciate any significant difference between the IDAS and the Loglow.  I've attempted to minimize processing to color balance and matching digital development:
IR/UV

IDAS

Loglow

blink:

stack of 9x120 sec exposures, color balanced by eye followed by digital development in maxim.

Iris Nebula

Last was the Iris nebula, a reflection nebula surrounded by dust in the dreaded northern muck, again with the FS 102 at F6.  As there appeared to be a significant color difference in the reflection component, the images were color balanced with x-calibrator.  The reflection component appeared significantly more blue with the IDAS and Loglow compared to the IR/UV filter.  I am not certain whether this is the result of grey light pollution contaminating the IR/UV images or enhanced color by the IDAS and Loglow due to rejection of signal in the middle of the color spectrum.  In any event, I found the effect aesthetically pleasing.

IR/UV

IDAS:


Loglow:


stack of 19x5 minutes color balanced with x-calibrator, ddp in maxim.

An aggressive histogram stretch in maxim showed the worst gradient with the IR/UV and best with Loglow, though the IDAS was close.

IR/UV

IDAS

Loglow

I did shoot some luminance with the two filters, but the background signal was so high with 2 minute subs, that it reached the non-linear region of my camera, making flats ineffective.  Between hot spots and dust specks it was difficult to make any comparisons.

Signal:
I compared the stellar, nebular, and background signal for a representative section of the M27 stacks and found the following:
For all of the quantities, the Lowglow had higher signal than the IDAS; the IR/UV the highest signal of all. 
However, for the ratio of stellar signal to background and nebular signal to background, the IDAS had the highest ratio, followed by the Loglow, and then the IR/UV filter.


idasloglowir/uv
M27 background1,2802,2302,890
star27,77727,92830,110
fwhm2.031.741.75
nebula (color balanced)177927333388
nebula (unbalanced)167227453400
star/background21.7012.5210.42
nebula/background1.391.231.17
nebula(unbalanced)/background1.311.231.18




iris background3,5005,3767,257
iris star19,000 21,000 28,000
fwhm1.681.981.76
excalibrator green0.930.991.03
excalibrator blue0.760.811.16
star/background5.433.913.86

Takahashi Fs 102 @619 mm Hutech IDAS LPS-P2/Choroma LoGlow, Starlight Xpress H9C/H9
M 27 34x2 minutes RGB, IRIS ~100 x 2 min luminance, 84x5 min RGB
9/15-9/24/14 Neport Beach, CA

Bottom Line

The two filters were comparable in terms of reducing light pollution gradients and enhancing nebular emissions.

The LoGlow seemed to be slightly better than the IDAS-P2 in terms of light pollution gradient reduction.

The LoGlow also passed more signal while the IDAS-P2 had a higher signal to background ratio. 


clear skies