HCG082

HCG 82 consists of 4 galaxies in far western Hercules west of the Keystone. It consists of 3 NGC galaxies and one PGC galaxy, NGC 6161-6163 and PGC 58231. The three NGC galaxies were discovered by Édouard Stephan on June 30, 1870. Hickson had no distance data when compiling his 100 groups. He assumed most would be related due to their close proximity to each other. In this case, they may be related though their redshift shows a rather wide range of values from about 460 million to 530 million light-year distance, a 70 million light-years difference. This is probably due to their orbital velocities around a common center of gravity and not a real distance difference. An average would put them just under a half billion light-years distant. I measure the group as being about 530,000 light-years across assuming they are all at about the same distance. NGC 6162 is the big one at 185,000 light-years across. NGC 6163, thanks to its wide "wings" is 125,000 light-years in size. NGC 6161, thanks to its plumes is nearly as large as NGC 6162 at 180,000 light-years though I suspect its mass is much less. Also, this size argues strongly against it being an irregular galaxy though its core region with the dust lane is only 65,000 light-years in diameter. PGC 58231 is the baby also at 65,000 light-years. Still a respectable size for a spiral galaxy.

NGC 6161 is listed as an Irregular Magellanic galaxy by NED while Seligman and the NGC project say Sc though Seligman adds a question mark. I see it as a disrupted spiral. I suppose its distortion is due to interaction with one or more of the other galaxies in this group. Only NGC 6163 appears possibly distorted so I'll say it is the cause. But if NED is right it may be just naturally this way.

The annotated image shows a scattering of other galaxies that have a similar redshift to those of HCG 82. All appear to be dwarfs compared to the 4 HCG galaxies. There is the usual mix of distant galaxies and quasars in the field. Nothing caught my eye as interesting, however.

As with many of my spring images, sky conditions were poor when this was taken. At least seeing wasn't all that horrible but there was a thick haze in the sky. 7th magnitude HD 148616, the K0 star to the lower right cast a glare from the haze over the entire image. Removing it was a major pain. Also, the haze severely harmed the blue image to the point it was very noisy. I should have taken more blue frames but the clouds didn't allow it this night and after this, the moon was a major problem. I went with the poor color data though as I've mentioned several times before the color is rather suspect due to high noise in the blue data. Also, clouds were kind to the first green frame but totally eliminated the second green frame. Still, it's one frame had a much higher signal to noise ratio than the two blue frames.

14" LX200R @ f/10, L=4x10' RB=2x10' G=1x10', STL-11000XM, Paramount ME

Related Designations for HCG082

HCG084

HCG 84 is a group of 6 galaxies in Ursa Minor, The Little Dipper, a bit northeast of the bowl. 5 of the galaxies are about three quarters of a billion light-years distant while the 6th is twice as distant at 1.39 billion light-years by redshift. Hickson made the assumption that if a galaxy was similar to the others in the group it likely was the same distance. He knew there'd be exceptions. I measure the size of HCG 84A at just under 200,000 light-years so it is a huge E2 galaxy. Obviously, its gravity is anchoring the group. HCG 84E is the smallest galaxy of the group at only 36,000 light-years. Distant HCG 84F is twice as large at 67,000 light-years, its greater distance making it appear nearly as small.

Hickson apparently lettered the galaxies in a group with A being the brightest and on down the magnitude scale. In this case, 84B and 84C appear reversed with C being 0.04 magnitude brighter than B according to NED. I assume this difference is so small that the magnitudes Hickson had available may have easily been the reverse. Being small and the most distant 84F is the faintest at magnitude 18.42 while A is magnitude 15.77 thus barely visible to say a 20" telescope under dark skies.

Being very far north at 77.75 degrees the field is poorly studied. I found redshift values for only the Hickson group galaxies. NED lists only 19 other galaxies in the area, a couple are out of my field. None have even a magnitude estimate let alone distance data. This makes for a rather sparse annotated image but I felt it needed to identify the members of the group.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Related Designations for HCG084

HCG23

HCG 23 contains 5 galaxies and is located in northwestern Eridanus. Unfortunately, it is quite low in my sky. In the fall warm water and cold air above results in both poor seeing and a lot of rising water vapor. Both make imaging this low virtually impossible. This image is obscured by over 2 magnitudes because of these issues.

HCG (Hickson Compact Groups) are a visual group. They need not be related. Usually, most are but often one or more galaxies is just a line of sight member. This group consists of 5 galaxies, A through E. E is the odd man out with a redshift twice that of the other 4 showing it a distant interloper. The other 4 are about 200 to 210 million light-years from us. The fifth being 450 million light-years distant. Also, a compact group is just that -- compact. Other related galaxies are usually in the area, just too distant to meet the compact requirement. Hickson set several requirements for his groups. They must contain 4 or more galaxies that vary no more than 3 magnitudes in brightness. They must be compact enough that the average surface brightness is brighter than 26th magnitude per second of arc. Also, they must be isolated so not the core of a galaxy cluster. For more on this subject see: http://ned.ipac.caltech.edu/level5/Sept01/Hickson/Hickson_contents.html .

There are many other members of the same group that four of the 5 members belong to. This larger not compact group is centered about NGC 1208 on the far right of my image.

Galaxies in compact groups are often interacting, hence the desire to located such groups. Two of the 5 galaxies in this group certainly look like they've interacted. NGC 1215 is a peculiar spiral with an inner ring around the nearly invisible bar that spawns two wide arms that form an outer ring. MCG -02-08-050 has an off center core surrounded by a blue ring. The other two true members, NGC 1214 and NGC 1216 appear rather normal.

I measure NGC 1214 at 90,000 light-years, NGC 1215 at 110,000 light-years, NGC 1216 at 70,000 light-years and MCG -02-08-050 at 34,000 light-years in size. The interloper, MCG -02-08-54 is 70,000 light-years across. But the big galaxy in the image is NGC 1208 at 140,000 light-years, a giant spiral indeed. But the real giant is IC 1880 at over 260,000 light-years in diameter.

NGC 1208 was discovered by William Herschel on January 10, 1785 but isn't in either H400 program.
NGC 1214 and 1215 were discovered by Ormond Stone sometime before October 12, 1886 and by Lewis Swift on October 21, 1886.
NGC 1216 was discovered by Ormond Stone sometime in 1886.

Normally I'd have moved the field east but I wanted to pick up the obvious flat galaxy in the upper left corner. There's no distance info available at NED for it, however.

Conditions for this image were lousy so it is a candidate to be retaken. I doubt that will happen, however.

14" LX200R @ f/10, L=4x10 RGB=2x10, STL-11000XM, Paramount ME

Related Designations for HCG23

HCG71

This field made my to-do list for two reasons. First is the galaxy NGC 5008 which has some fascinating plumes and houses an AGN at its core. Both indicate it has recently interacted with or devoured another galaxy. Also, it is the major galaxy in the Hickson Compact Group 71. I'm slowly working on those that interest me as well. The field is located in Bootes.

NGC 5008 is classified as Scd: by NED; SBc by the NGC Project; and SBc? by Seligman. So does it have a bar or not? Maybe. I can see arguments both ways. Its arm structure is weird for either barred or not barred spirals. While there's a hint of arms starting from a very faint bar they die out quickly and spiral counterclockwise. Other arms start from nothing and go for much further and are often brighter yet spiral clockwise. They are also bluer than those coming off the possible bar. An inner counter-clockwise and outer clockwise spiral pattern with plumes would indicate some sort of merger. I find it odd no one tacked on the peculiar label. By redshift it is some 430 million light-years distant though non-redshift measurements put it slightly further.

It was discovered by Heinrich d'Arrest on May 18, 1862. But unfortunately he recorded its hour angle one hour off and noted the nearby 10th magnitude star as being north when it is south. I've greatly dimmed it in my image so it appears much dimmer but still the brightest of the three to the south as otherwise its glare was very distracting from the galaxy itself. It was then recorded as NGC 5008 at the wrong position. So when Stephane Javelle later found it on June 15, 1895 and recorded its position correctly it became IC 4381. It was only later that d'Arrest's error was discovered and the two realized to be the same galaxy. Then Hickson in recording his compact galaxy groups included it along with IC 4382 and two others (see the annotated image) as his group #71. We now know that while three of these galaxies are likely related and have similar cosmological redshifts HCG 71D has a redshift putting it twice as distant as the other three. I notice NED, while listing all four as part of the group gives the count for the group at 3, not 4. Is it excluding this more distant member?

The other four are IC 4382, HCG 71B, which also houses an AGN and is listed as an Sb edge-on spiral, PGC 50640 which is HCG 71C is listed as an Sbc spiral and the outcast PGC 50641/HCG 71D listed as an S0 galaxy at 910 million light-years. It is also the furthest from the center of the group. There appear to be other galaxies in the area that are members of the group as they too have redshifts very similar to that of NGC 5008. LEDA 214226 to the north may appear to be double in my image but the northern object is a very blue star and ultraviolet source. Then to the northeast is LEDA 1741935 which has a very off-center core making it look like a comet. It too shares about the same redshift. More ordinary looking is LEDA 4405543 to the east-northeast. It is the smallest of the group. To the north-northeast is the very low surface brightness apparently spiral LEDA 4556417. Another dwarf member of the group is LEDA 4404962 far to the north. But even further north is NGC 5498 a large S0-: galaxy that too shares the same redshift and looks possibly the most massive of the group. Others are found outside my field.

NGC 5498 was discovered by Edouard Stephan on May 9, 1882. NED lists it as S0 while the NGC Project says E-S0. It is a very large galaxy some 160,000 light-years in diameter. NGC 5008 is much larger, 280,000 light-years, if you include the plumes but the spiral itself is only 90,000 light-years in diameter. IC 4382 is actually larger at nearly 110,000 light-years but seen edge on appears much smaller. I find it odd it has no dust lane visible. It too was found by Stephane Javelle at the same time as he saw NGC 5008/IC 4381. While he made a one minute error in the position of both their relative positions match perfectly.

HCG 71C, an Sbc spiral is only about 65,000 light-years across. About the size of an average spiral. HCG 71D is about 100,000 light-years across. Only is greater distance makes it appear smaller than the other three. Of the other galaxies related to NGC 5008 and NGC 5498, LEDA 4405543 is the smallest of the group in my frame at about 23 million light-years.

While HCG 71D isn't a true member of the group it does appear to be part of a different group of galaxies seen scattered over the image. However, I found no cataloged group for either of these two other than part of the closer being part of HCG 71. Considering how many strange galaxies are in the closer group I'm surprised it hasn't received any significant attention.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Related Designations for HCG71

HERC CLUSTER

The Hercules Cluster, Abell 2151, is a rather unusual galaxy cluster a bit under a half billion light-years distant. It is unusual for its high content of spiral galaxies. Most clusters are mostly elliptical or S0 class galaxies due to most being the result of many galaxy mergers over billions of years. Somehow this cluster has avoided this though even a quick examination of my image shows many spirals in the act of merging or at least colliding. In fact, four of them made Arp's Atlas of Peculiar Galaxies, Arps 71, 122, 172 and 272. of the four only Arp 172 doesn't involve spiral galaxies. Many other galaxy interactions are also seen in my image. I prepared an annotated image but it is so cluttered with labels maybe I shouldn't have labeled as many as I did.

This is one of earliest images and suffers from my inexperience. The data was taken back in 2007. Though reprocessed 9 years later from scratch my calibration frames were crude so loses a lot. I keep saying I'm going to retake it but it never happens. Mostly because seeing is poor when it's best positioned and when seeing is good there are so many things still on my to-do list that have never been taken that it hasn't yet happened.

14" LX 200R @ f/10, L=6x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Related Designations for HERC CLUSTER

HH389

This interesting field in Cygnus just under 6 degrees due north of the North American Nebula. I've centered on the variable star V1331 Cyg. It harbors HH389 and lights up the reflection nebula around it GN 20.59.5.01 forming an arc around the variable star. SIMBAD notes that while some consider the star an FU Orionis class star they say this is unlikely though it is a young stellar object so likely a star just coming onto the main sequence. It has a G5 spectrum so a bit redder than our sun. The reflection nebula is the dust left from the creation of the star that's lit by the star it created. As such it takes on pretty much the color of the illuminating star. Radiation pressure from the star likely created the arc as it pushed away the dusty cocoon of its birth. The star seems out of center indicating this dust may be piling up at a shock front as it moves through the very dusty interstellar medium in this part of the galaxy. I found no papers on this so am just speculating here.

The dark nebula complex running southwest (down and right) from the star is LDN 981. It appears something like a trident with an overly long central prong. The dark nebula in the lower left corner is LDN 984. Most of it is out of my frame. A bright star is out of the frame to the left center. It cast a very nasty set of bright streaks onto the image. I thought it far enough away not to be a problem. My crude attempts to process out the streaks may have done more damage than leaving the streaks in.

One paper puts the entire complex of the star, emission and dark nebula at a distance of 0.8kpc which is 2,600 light-years. http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1994ApJS...95..419D&db_key=AST&nosetcookie=1

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Related Designations for HH389

HindsVarNb NGC1555

NGC 1555 is one I imaged before but in a short exposure. It's known as Hind's Variable Nebula. It is lit by T Tauri, a variable star surrounded by dust clouds. Some of the variability is due to these obscuring the star though most are due to the star itself. But these clouds also can shadow NGC 1555 causing part or all of it to dim and brighten.

In my first shot I picked up some faint nebulosity all through the field but it was so down in the noise as to be nearly invisible. My goal was to bring this faint cloud out. NGC 1555 just was in the way. It is a reflection nebula lit by a rather well studied very young star known as T Tauri. They are so young their nuclear furnace hasn't yet started fusing hydrogen to Helium. Some Lithium fusion may be going on but their main source of energy is gravitational collapse. They are still shrinking down to size. When they reach the right size the temperature and pressure in their core will cause the nuclear furnace to start to fuse hydrogen. So this is a star just being born. It likely came out of the huge cloud behind it. Infrared shots show this cloud full of forming stars. But so far none are hot enough to light it up like more famous emission nebula like the Orion Nebula so they are mostly dark. But if you expose long enough they do shine by the light of the rest of the stars in our galaxy reflecting off of me. That's what I'm mainly trying to photograph here. Right beside T Tauri is NGC 1555 which is a denser bit of dust and gas likely blown off as T Tauri formed. Its light is now pushing this small molecular cloud away. In the link below note that photo shows stars not seen in my shot. It's an infrared image so shows stars in the cloud invisible in visible light. But the two HH objects it mentions are unseen in the IR shot but show well in mine as the two objects "dangling" from T Tauri. They emit only in visible light so weren't seen in the IR image. Nor is the molecular cloud itself for the same reason.

You can read more about such stars at http://en.wikipedia.org/wiki/T_Tauri

Now for the 9 asteroids. The one at the bottom left is unknown to the Minor Planet Center which is the clearinghouse for asteroids. Meaning I again missed finding a new asteroid thanks to clouds. Though in this case, I didn't even look at the shots until just a few days ago so even if it had been clear I'd likely have not seen it until too late to try and pick it up again. I've got to learn to check my shots immediately for such things. With 383,912 asteroids now known and thousands being found each month by patrol cameras I didn't realize how many unknown ones are still out there! I need to start looking hard at photos taken near the ecliptic like this one was, being only about 3 degrees south of it. Prime asteroid territory.
The remaining asteroids and their predicted magnitudes that night are:
49066 1999 RN53 18.9
165913 2001 TF8 17.9
30907 1993 FD47 19.7
2005 GW218 19.9
2007 VY238 20.1
168504 1999 TL15 19.8
2003 QU94 19.2
97705 2000 GM77 19.8

The naming system is interesting. The year is obvious. The first letter tells you when it was found in the year. A means Jan 1 to Jan 15. B the rest of January, C the first 15 days of February etc. "I" is not used however to avoid confusion with 1. The first asteroid found in January 2008 would have the name 2008 AA The second 2008 AB. After 25 are found we are out of letters so the process starts again with 2008 AA1 which would be the 26th asteroid found that half month. 2008AB1 would be #27, after 50 then the subscript is 2. So the process is to multiply 25 by the number after the letters and add the position of the second letter not counting I. So we know 2007 VY238 was found the first half of November 2007 and was the 5974th asteroid discovered in that 15 day period. (238*25+24) That's a lot! But the discovery rate is even faster now with more automated surveys online. Since I wrote this the number of known asteroids has more than doubled to 762080 according to the Minor Planet Center (July 16, 2017).

Edit: Since I wrote this my unknown asteroid has been found. In fact, it was discovered a month before the image was taken but hadn't been confirmed so wasn't in the Minor Planet database. It is (361716) 2007 VM321 at magnitude 19.3. While discovered only a few days after 2007 VY238 mentioned above it wasn't listed when I did my research. I suspect there was a problem defining its orbit. Note that while only a few days passed the number of asteroids found that period was another 2000 were found.

For reasons lost to history, I took this image at a resolution of only 1.5" per pixel. Again, likely due to my inexperience back in 2007.

14" LX200R @ f/10, L=7x10'x3 RGB=2x10'x3, STL-11000XM, Paramount ME

Related Designations for HindsVarNb NGC1555

HOAGS OBJ

Hoag's Object is the name this galaxy got when first discovered by Art Hoag in 1950. It is about 600 million light years distant and about the size of a typical large spiral galaxy like our own Milky Way. Hubble imaged it in its high resolution though the image uses false colors so the core is an odd yellow color. Oddly, there's a much more distant ring galaxy seen through the gap between the core and the ring. It shows as only a discoloration in my image.

The Hubble image is at:
http://apod.nasa.gov/apod/ap040815.html

You can read more about these oddball galaxies at:
http://heritage.stsci.edu/2002/21/lucas_files/lucas.html
See the link below for a photo taken at Kitt Peak of this galaxy and read their take on it.
https://www.noao.edu/kpvc/Prog/galaxy1.php

Two satellites went through the field while I was taking this image, one is faint to the right of Hoag's object the other obvious. Back in 2007 when my image was taken I didn't have the ability to easily remove satellites. I've not reprocessed it the data to remove it.

14" LX200R @ f/10, L=4x10' RGB=1x10', STL-11000XM, Paramount ME

Related Designations for HOAGS OBJ

HOCR1

On the nights of February 2, 4 and 11, 2006 Australian amateur astronomer Michael Howell took a narrow band image of the Jellyfish supernova remnant and SH2-249 as many amateurs before he had. But a small object in his wide field caught his eye. Was it real? Amateur Richard Crisp was called in to see if he saw it. He did. But it wasn't in any catalog. It turns out it is a rather bright and large planetary nebula no one noticed despite it being imaged a zillion times by professionals and amateurs. Or if they did notice it they just ignored it. Fortunately, Mr. Howell investigated and now the planetary is known as HoCr1. So how many amateurs had a chance to have this rather obvious planetary nebula named for them and lost out as they only paid attention to the object they were imaging, IC 433? An APOD image from May 15, 2010 https://apod.nasa.gov/apod/image/1005/ic443_franke.jpg , of the area, shows it but never mentions it is in the image. This was 7 months after its discovery was announced.

I was surprised to find it still isn't listed in Simbad. You can read Mr. Howells story and see his discovery images as well as professional ones at http://www.horizontalheavens.com/planetarynebulaproject.htm . That link leads to the paper about it and many other newly confirmed planetary nebulae.

It seems all images of it I find are narrow band or if RGB are so low scale not much can be seen in it. None show its central star. What looks like a central star in the narrow band images is the bright star that happens to lie at its core. But my LRGB image shows it as somewhat red so not the true central star. Look just below it and peeking out from its glare is a very blue star. I assume it is the true central star.

Faint H alpha emission from Sharpless 249 lies across my image but with my short exposure time in broadband it isn't very obvious but for a brighter patch with a dark hole along the bottom left of my image.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

Related Designations for HOCR1

HOLMBERG I

Holmberg I is the first of 9 dwarf galaxies in Holmberg's list of dwarf galaxies, most of which lie somewhat in the area of M 81. Holmberg 1 lies about 2.5 degrees northwest (330°) of M81 and is considered part of the M81 group. It is a very blue, low surface brightness dwarf with little HII emission according to papers I read. That surprised me as the HST image shows some nice nebula in it. Then I noticed the filters used by the HST, Green (centered on the same frequency as most green lasers, 555nm) was assigned to blue with near infrared, 814nm, was assigned to red. Thus the blue nebulae were seen in green light rather than H alpha red. They show as blue fuzzy "stars" in my image and are quite weak in red light. I need to revisit this one in H alpha sometime.

The redshift distance is 10 million light-years but this is highly unreliable so close in. Still, the non-redshift values show it only slightly further. They range from 12.5 to 19.2 million light-years. Three values were derived from the HST images, some of which I used for my rendering. Those are in quite close agreement with the latest having the value of 13.0 million light-years which I show on the annotated image. An older paper puts it at 12 million light-years. New data supports the 13 million light-year distance. Otherwise, the paper is interesting but rather deep. http://iopscience.iop.org/1538-3881/122/6/3070/pdf/1538-3881_122_6_3070.pdf

I got quite a shock when I had NED list the objects of all types in the field with redshift data. It returned only Holmberg I. So I asked for all galaxies or galaxy clusters and quasars or quasar candidates. That returned only three others! One is barely visible on the FITS stack but almost invisible on the processed TIFF file. After JPG compressing it is gone unless you hype the brightness greatly. It is listed as being possibly a dwarf spherical galaxy. Its position is somewhere in a 5 arc second circle but that does include the faint fuzz patch I've marked. The other galaxy right near Holmberg I is bright but near star-like until you look at its PSF. One star is listed as a strong ultraviolet source by the Galex satellite and is considered a candidate quasar though with no redshift and little else I could find on which to make this claim.

When I asked for all objects it did return 3 HII regions. Two agree with tiny blue "stars" in the galaxy in my image.

Of the 9 Holmberg galaxies, I'm yet to catch VI. It is at -21.3° so too low unless I have a one in a thousand night. Holmberg II is filed under Arp 268 and Holmberg IX is in my image of M81 if you are looking for those two. The rest are under their Holmberg designation.

You can read more about Holmberg I at this PDF link. It gets a bit deep and precedes the later distance estimates I used. http://iopscience.iop.org/1538-3881/122/6/3070/pdf/1538-3881_122_6_3070.pdf It indicates the galaxy is undergoing ram pressure stripping.

14" LX200R @ f/10, L=4x10' RGB=2x10' STL-11000XM, Paramount ME

Related Designations for HOLMBERG I