Wednesday, 21 August 2013

Treasure Island: Camelopardalis the Giraffe

Camelopardalis the Giraffe is one of the (most) neglected constellations in the sky despite being 18th largest. Petrus Plancius (introduced Camelopardalis in 1612)[1] probably made a bit of a mistake adding a giraffe so close to the north celestial pole. I mean a giraffe! What ever happened to, say a moose? No wonder the poor giraffe's so alone, far far away from her home. And frightened: it is surrounded by two bears (Ursa Major & Minor), a lynx (Lynx), a dragon (Draco) and an angry charioteer (Auriga)! And when you're next to Perseus the hero, Cassiopeia the queen and Cepheus the king... no wonder you're feeling a bit unappreciated and it is quite understandable why you're facing away from those three.

Kidding aside, your typical observer probably knows NGC 1501 + NGC 1502 and NGC 2403 from the constellation. What one really shouldn't miss are the three fine and bright IC galaxies (IC 334, IC 342 and IC 356), fairly recently discovered open cluster Alessi 2 and a huge bunch of fine NGC galaxies worth browsing! Be sure to check out NGC 2366 - 3 bright HII regions (around 12th magnitude!) visible better than the parent galaxy itself. With larger apertures you can try to locate the elusive EGB 4, try to see the spiral structure in NGC 1530, NGC 1961 and NGC 2146 or zoom in on IC 361's tiny stars glittering with stardust. Without further ado, here are some of the treasures from Camelopardalis.

Alessi 2
Size: 30'
Type: IV 3 m
Notes: Br * 8.8
EGB 4 (Ellis-Grayson-Bond 4 / PK 144+24.1)
Magnitude: 12.5 (v)
Size: 1.7'
Type: ?
Notes: Central star 12.7 (v), very low surface brightness.
GSC 3719-1528 group
Size: 0.2'
Type: II 1 p (asterism)
Notes: Br * 13.4
IC 334
Magnitude: 11.3 (v)
Surface brightness: 12.9
Size: 2.5' x 2.1'
Type: I/P
Notes: Material bridge(?) racing towards south.
IC 342
Magnitude: 8.4 (v)
Surface brightness: 14.9
Size: 21.4' x 20.9'
Type: SBc
IC 356 (Arp 213)
Magnitude: 10.6 (v)
Surface brightness: 13.9
Size: 5.9' x 3.9'
Type: Sb/P
IC 361
Magnitude: 11.7 (v)
Size: 7.0'
Type: II 1 r
Notes: Br * 14.0
IC 3568 (UGC 7731)
Magnitude: 10.6 (v)
Size: 18" x 18"
Type: 2 (2a)
Notes: Central star 11.4 (v).
Mayer 2 + Sh2-207
Size: 3.0'
Type: III 1 p n
Notes: Surrounded by emission nebula Sh2-207.
NGC 1501
Magnitude: 11.5 (v)
Size: 52.0"
Type: 3
Notes: Central star 14.4 (v).
NGC 1502
Magnitude: 6.9 (v)
Size: 7.0'
Type: I 3 m
Notes: Br * 9.2
NGC 1530
Magnitude: 11.5 (v)
Surface brightness: 13.9
Size: 4.4' x 2.5'
Type: SBb
NGC 1560
Magnitude: 11.4 (v)
Surface brightness: 14.4
Size: 9.8' x 1.5'
Type: Scd
NGC 1569 (Arp 210)
Magnitude: 11.0 (v)
Surface brightness: 12.9
Size: 3.7' x 1.8'
Type: IBm
NGC 1961 (Arp 184)
Magnitude: 11.0 (v)
Surface brightness: 13.7
Size: 4.5' x 3.1'
Type: SBbc
NGC 2146
Magnitude: 10.6 (v)
Surface brightness: 13.7
Size: 5.4' x 2.9'
Type: SBab/P
NGC 2366
Magnitude: 11.1 (v)
Surface brightness: 14.5
Size: 8.1' x 3.0'
Type: IBm
Notes: NGC 2366 = three giant H II regions SW side of the galaxy, NGC 2363 = another H II region to the W.
NGC 2403
Magnitude: 8.9 (v)
Surface brightness: 14.4
Size: 23.4' x 11.8'
Type: SBc
NGC 2460
Magnitude: 11.8 (v)
Surface brightness: 13.3
Size: 2.5' x 1.9'
Type: Sab
Notes: Interacting pair with IC 2209 (lower right), LEDA 213434 (above NGC 2460) is a background galaxy.
NGC 2633 & NGC 2634 (Arp 80)
Magnitude: 12.2 (v) & 12.0 (v)
Surface brightness: 13.6 & 13.1
Size: 2.3' x 1.5' & 1.7' x 1.6'
Type: SBb/P & E1
Notes: NGC 2634A = 13.5 (v) magnitude.
NGC 2655 (Arp 225)
Magnitude: 10.1 (v)
Surface brightness: 13.2
Size: 4.9' x 4.1'
Type: SB0-a
Stock 23
Size: 28'
Type: II 3 p n
Notes: Br * 7.6
Tombaugh 5
Magnitude: 8.4 (v)
Size: 15'
Type: III 2 r
Notes: Br * 14.0


References 
[1] http://en.wikipedia.org/wiki/Camelopardalis
Images courtecy of the Digitized Sky Survey (
STScI)
Magnitude data from "Revised NGC/IC Data 2013" by Dr. Wolfgang Steinicke

Thursday, 8 August 2013

Extragalactic objects - Beyond M31 and M33

As I'm preparing a little presentation of "EXTRAGALACTIC OBJECTS IN ANDROMEDA AND TRIANGULUM GALAXIES" to our annual Deep Sky Meeting, I thought to myself, why not dump some of that stuff in it here? As the goodies in Andromeda and Triangulum galaxies have already been discussed in the Blog, here are some of the  fancy objects included in the intro of the presentation.

Artist's impression of SagDEG
Image courtesy of NASA
If you consider SagDEG and Canis Major Dwarf as extragalactic and "not enough bound to the Milky Way", the hunt for the extragalactic objects becomes quite a lot easier. With SagDEG (size 7.5° x 3.6°), one can simply spot M54 (NGC 6715) with a pair of binoculars and say they've logged an object from another galaxy. With this in mind, it is interesting to point out that it was Charles Messier in 1778 who was the first person to have spotted an extragalactic object from another galaxy! Is it true? Of course not. 30 Doradus (NGC 2070) was seen by Nicolas Louis de Lacaille back in 1751 as well as the Aboriginals who must have spotted this object hundreds of years before Lacaille. How about the bulky 12°  x 12° Canis Major Dwarf? As with SagDEG, you can cheat a bit and consider the galaxy as extragalactic and simply spot one of these globular clusters: M79, NGC 1851, NGC 2298 or NGC 2808. The brightest star in the galaxy, that I managed to find out about, is EIS 7873 at magnitude 16.2. 

Large Magellanic Cloud
Credit & Copyright: Marco Lorenzi
No matter how you look at it, you don't have to cheat with the Large Magellanic Cloud (Nubecula Major / PGC 17223). This irregular galaxy was noted by al-Sufi (964) and Vespucci (1501) prior to Magalhães but I suppose "Large al-Sufi Cloud" or "Large Aboriginal Cloud" doesn't rhyme quite as well as “Large Magellanic Cloud”. Anyway, LMC harbors the brightest object in another galaxy (the brightest extragalactic object is of course LMC itself). It contains the gigantic (over 25 times larger than the Orion Nebula!) H II region 30 Doradus (Tarantula nebula / NGC 2070) which shines at an impressive magnitude of 4.0[1]. Considering it is an easy naked eye object, the typical apparent magnitude of 8.0 (v) can be considered far too faint. The brightest star in LMC and also the brightest extragalactic star in the sky is S Doradus at 9.5 (v) magnitude (8.6 to 11.5 var). SMC (Nubecula Minor / NGC 292) comes far behind but it contains the conspicious H II region NGC 346 with a magnitude of
6.0-6.5 (v)[2]. The brightest single star in SMC is HD 5980 at 11.3 (v) magnitude which is located inside NGC 346.

After these two (or four, you little cheater...) it becomes a bit trickier. In the Andromeda-piece the extragalactic globular clusters in Fornax Dwarf (Spheroidal) where mentioned. Of the bunch the brightest one is  NGC 1049 @ 12.6 (v) magnitude so it can be spotted even with small apertures. Despite the bright globular clusters, the brightest single stars in Fornax Dwarf are only around 19th magnitude! The hunt for individual stars becomes easier with NGC 6822 (Barnard's galaxy). The brightest stars shine around 15th magnitude so resolving the galaxy should be fairly easy but identifying a star that actually is part of NGC 6822 and seeing it (not just a bunch of resolved stars) is going to be annoying. Oh, and don't forget to bag the brightest H II region in NGC 6822: IC 1308 which shines at around 14th magnitude. Don't get freaked out by the larger aperture sightings of it by Jakiel, Gottlieb, Polakis[3]. IC 1308 is quite visible even with medium apertures.

For globular cluster hunters, here's a list of brightest extragalactic globular clusters.
Host galaxy
Name
Mag (v)



Fornax Dwarf
NGC 1049
12.6
Andromeda galaxy
G1
13.7
NGC 205 (M 110)
G73
14.9
WLM
WLM 1
15.7
Triangulum galaxy
C39
15.9
NGC 147
Hodge 3
16.5
NGC 185
Hodge 5
16.6
NGC 2403
F46
17.5
Messier 81
[PR95] 50225
18.4


References
[1] Stephen O'Meara. Deep-Sky Companions: The Caldwell Objects: page 406.
[2] Visual magnitude estimate by Timo Karhula.
[3] http://www.astronomy-mall.com/Adventures.In.Deep.Space/barnard.htm
 


Saturday, 3 August 2013

Extragalactic objects in Andromeda galaxy (M31)

The Andromeda galaxy / Messier 31

Even though the H II regions in the Andromeda galaxy are not as prominent as the ones in the Triangulum galaxy, this bad boy beats M33 in globulars that's for sure. When compared to the Triangulum galaxy, ten of the brightest globular clusters are between 13.7 and 14.9 magnitude (15.9 - 17.6 in M33). In total over 300 globular clusters have been identified from the galaxy. That's not all: there's a whooping 60 brighter clusters than 16th magnitude. Should you choose to pursue some of these objects, a good photograph is required. The image to the left shows only a handful of globular clusters, is very simplified and presents just a small part of the entire Andromeda Galaxy. A good place to start is the 1981 Atlas of the Andromeda Galaxy by Paul W. Hodge. Observing Handbook and Catalogue of Deep-Sky Objects by Skiff and Luginbuhl has a basic map on page 17. Night Sky Observer's Guide Volume 1 has a fairly good photography map of M31 on page 16. There is an obvious error though: G78 is marked at the wrong position. If you're looking for a very complete list of objects in M31, the best one is Star Clusters by Hynes & Archinal containing literally hundreds of objects.

Even though only the brightest globular cluster is introduced, I encourage everyone to try to observe as many of them as possible. Several of the extragalactic globulars can be seen even with small apertures between 4 to 6 inches. So far I've been able to detect 7 of the brightest globular clusters using my 4.7" Sky-Watcher under typical truly dark skies of Finland. If you live south enough be sure to log NGC 1049 (Hodge 3) located in the Fornax dwarf galaxy. This globular cluster beats Andromeda's G1 in brightness (by over a magnitude) as do the three other globulars in the same galaxy.


OB association NGC 206

RA: 00 40 31 Dec: +40 44 16
NGC 206 is the most prominent object in the entire Andromeda Galaxy. What I can remember about this star cloud is that it should be "kidney-shaped" and it slightly is. Still, have we really gone so low that we're spotting kidneys at the eyepiece these days? Apparently so! In any case, NGC 206 is so bright and obvious under good conditions that I wouldn't be surprised if someone came forth and claimed it to be visible with a pair of binoculars. It is just so conspicuous and cuddly even using a simple 3 inch telescope. With little research it seems like the brightest star in the NGC 206 association and in the entire Andromeda galaxy is #12 by a paper by Odewahn (1987) at magnitude 16.0 (v). The star is marked in the image on the left.










OB association A 54


RA: 00 44 33 Dec: +41 52 30
This association is nearly as large as NGC 206 but a lot fainter. Generally listed as a magnitude 16 object it still is visible with medium apertures such as 8 to 10 inches of aperture. It appears as a NE-SW elongated, slightly mottled patch of light in the near the NE tip of the galaxy. It is even mentioned in the 1998 (2. edition) Observing Handbook and Catalogue of Deep-Sky Objects as being visible in a 10" telescope.















H II region C 410


RA: 00 44 25.1 Dec: +41 20 42
C 410 is the brightest H II region (+ and open cluster) in the Andromeda galaxy according to the book Atlas of Messier Objects. The object is located between the globular clusters G272 and G280. Not much else can be said about it as I have not seen this object myself.

















Globular cluster G1 / Mayall II / NGC-224-G1 / SKHB 1


RA: 00 32 46 Dec: +39 34 40
As even the image above shows this is a big boy - especially when you keep in mind the distance of at least 2.5 million light years. As an example the remote globular cluster NGC 2419 is roughly 300 000 light years away. It is still uncertain if this object is actually a dwarf galaxy or simply a giant globular cluster. Compared to the biggest globular cluster in our Milky Way, Omega Centauri, G1 is twice as massive.[1]

G 1 forms a tight triangle with a pair of nearly 15th magnitude stars. With small apertures and small magnification this group forms a single, stellar point of light. Many observers say that in order to claim G1 as seen, one should resolve it from the two nearby stars. This can be done with small apertures such as 4 to 6 inches but requires high magnification and so good seeing as well. However, claiming G1 as seen does not require you to separate these two faint stars from the cluster. The non-stellar appearance is quite easily achieved even under suburban skies using 6 to 8 inches of aperture.

Finding G1 might require a bit of patience if you're unfamiliar with the field or star hopping in general (for some reason). Tom Trusock wrote in his 2006 Small Wonders column that: "While it's not a toughie to see - if you have sufficient aperture - it can be a real pistol to find."[2] I assume this means that G1 difficult to find but it makes me wonder why. Maybe it is aperture related? To me the globular is basically just two star hops away. I will not go into specifics but I will explain you which one I use and the one I think is the easiest. First locate the 5th magnitude star 32 Andromedae which should be visible at least with your finder. From this star simply move to the north-west until you locate the 7th magnitude star HD 2993. This star has two fainter stars to the south the last one in line is 9th magnitude PPM 65429. From here, move less than 15' to the west and here is G 1. The key is just to get the finder and/or stars orientated the right way. Once you get it, rest is easy.



Star AF Andromedae

RA: 00 43 33.1 Dec: 41 12 10

The hypergiant AF And is one of the most luminous stars known with an absolute magnitude of -10.6 (our Sun is +4.5). This irregularly variable LBV is generally fainter than 17th magnitude but has had two brief eruptions in 1970-1974 and 1987-1992 when it was somewhere in the 16th magnitude. When measured between September 1992 and January 1993 (by Szeifert, T. et al.) it showed some variability from 16.91 to 17.14 magnitude.[3]













Star AE Andromedae


RA: 00 43 02.5  Dec: +41 49 12
This too is a bit on the heavy side although not as massive as AF And. With an absolute magnitude of -9.4 it still ranks high (top 20) in the most luminous list. As with AF Andromeda, this is a LBV star which has irregular eruptions. The last eruption was back in 1928 when the star flared up (and was also discovered for the first time) to an impressive object brighter than 15th magnitude. Between September 1992 and January 1993 CCD photometry was taken from the the star and it showed only a little variability: 17.56 - 17.59.[3]














Star A1 Andromedae

RA: 00 44 50.57 Dec: +41 30 38

This star is located in a H II region A41. Out of the three most well known LBV stars in Andromeda galaxy, A1 And is the brightest. Once again photometry obtained between September 1992 and January 1993 showed this giant star at 16.18 - 16.59 magnitude.[3]
















References:

Atlas of Messier Objects. Ronald Stoyan et al. 2008.
[1] MAYALL II = G1 IN M31: GIANT GLOBULAR CLUSTER OR CORE OF A DWARF
ELLIPTICAL GALAXY? G. Meylan et al. 2001. http://arxiv.org/abs/astro-ph/0105013
[2] Tom Trusock. Small Wonders: Deep Andromeda Satellite Galaxies, Star Clouds and Globular Clusters of M31
[3] HST and groundbased observations of the `Hubble-Sandage' variables in M 31 and M 33. Szeifert, T. et al.
Images copyrighted by The Digitized Sky Survey.

Extragalactic objects in Triangulum galaxy (M33)

The Triangulum galaxy / Messier 33

The Triangulum galaxy is the best galaxy in the northern hemisphere when it comes to extragalactic objects. The easiest targets in M33 are the numerous H II regions and stellar associations. Globular clusters are numerous, but a lot fainter than the ones in Andromeda Galaxy, with ten brightest ranging between magnitudes 15.9 and 17.6.

There is a little problem when it comes to the H II regions. Finding an appropriate designation for an object can be quite a mess. This is mostly thanks to Guillaume Bigourdan whose original coordinates are inaccurate. Feel free to blame all the modern authors as well. They can't seem to be able to make up their minds which object is which. If you look at two modern sources and try to match the designations together, you are quite often in for a treat! The identities of NGC 588, 592, 595 and 604 are pretty certain. With the IC objects it isn't quite so. Several sources seem to agree on IC 135, IC 136, IC 132 and IC 133 as well. NGC/IC-project has a pretty good base but since you can't ask directly from Bigourdan himself, their fixed are guesses and estimates at best no matter how good, convincing and true they might be. There are numerous differences and errors out there in different books, software and internet sites. Here are some just to name two:

IC 143 is labeled twice on NSOG Vol1 (page 392) obviously the region to the nucleus is IC 142.

IC 137 problem. "Atlas of the Messier Objects" show IC 137 at 01 33 11 +30 29 53. Megastar V5 shows the same object as IC 136 and a map with in article by Steve Gottlieb[2] plots the same region just as A 127 and show IC 137 far away at 01 34 14 +30 34 31. Where is IC 137?

So what to do? In my opinion the best bet is to name the few NGC and IC objects correctly, then use the association designations as listed in the 1991 paper "The stellar populations of M 33" by Sidney Van Den Bergh[1] since they're correctly listed in nearly all publications. At least for me this saves a lot of time and frustration but enough history, time to go forward with the actual objects.

H II region NGC 604


No introduction is needed when it comes down to NGC 604. The H II region is the bomb: it is nearly 1500 light years in size, estimated to come only second to the Tarantula nebula in the entire Local Group of galaxies. The Orion nebula truly pales in front of this nebula. With these characteristics, it is no wonder NGC 604 can be observed with pretty much any telescope and larger binoculars. With a modest size telescope it looks like a slightly elliptical glow with a brighter center. In my opinion, this is the easiest extragalactic object in the northern hemisphere. NGC 206 comes close but its appearance is more diffuse and surface brightness lower. The brightest individual stars in the central region of NGC 604 are roughly 16th magnitude.

Globular cluster C 39 (Mayall "C")


It might not look like much but it is something alright. Also known by its GSC number (2293:1339), C 39 has a visual magnitude of 15.9 so it is right at the edge of a good 8" telescope under pristine conditions. This will be a great challenge.

Globular cluster C 27


This second brightest globular cluster in M33 is considerably fainter than the previous one, being close to 17th magnitude visually although the commonly given v magnitude is 16.5. This will require larger aperture. Coordinates for this one are 01 34 43.7 +30 47 38.

Globular cluster U 49


These two globulars appear very faint in photographs but are usually listed as brighter than C 27. U 49 is located at 01 33 44.3 +30 47 32.9 and listed at 16.2 magnitude. The B magnitude for the object is 16.3.

Globular cluster U 62


U 62 (listed as U 43 in the book Atlas of the Messier Objects, page 155) is slightly fainter and located at 01 34 10.5 +30 45 48.7. This stellar point seems to be a double object, so the combined magnitude of these two are 14.8 (v). The globular is the fainter object of this two, listed as 16.5 magnitude.

Star B 342


This is it: the brightest individual star in M33 - if you exclude the LBV stars. Star known as B 324 is an A-type supergiant and lies just 6' from the center of M33 in the star association 67 (A 67) or IC 142. The v magnitude of this star is 15.2 but is this really in M33 or just another Milky Way star? Lundmark (1921) listed the brightest star in the galaxy to be 15.7 (B) magnitude. Humphreys, Massey & Freedman proved in 1990 that B 342 is indeed part of M33 and also the brightest in single star in the entire galaxy. Considering the magnitude, this should be a fairly easy catch with telescopes 8" and larger. Coordinates: 01 33 55.9 +30 45 30.4.

Star GR 290 (Romano's star)


This object is a LBV (Luminous Blue Variable) star. "It shows eruptions with amplitude of more than 1 mag and timescale of about 20 years and smaller oscillations with amplitude 0.5 mag and a period of about 320 days"[3]. The star varies between magnitude 16.5 and 17.8 so it isn't exactly for medium apertures. This star lies close to A 89. Coordinates: 01 35 09.7 +30 41 57.4.

Don't forget to check out the LBV stars Var B, Var C and Var 83 (absolute magnitude of -11.1!) in the galaxy. As with Romano's star, these are truly massive stars varying between magnitudes 15 down to 16.5 and from time to time display eruptions making them even brighter. For example Var C in M33 is listed as varying between magnitudes 15.2 - 16.5 making it in range to moderate size telescopes[4]. Good luck!


References:

Atlas of Messier Objects. Ronald Stoyan et al. 2008.
[1] The stellar populations of M 33. Sidney Van Den Bergh. 1991. http://adsabs.harvard.edu/full/1991PASP..103..609V
[2] http://astronomy-mall.com/Adventures.In.Deep.Space/M33.HII-Star.Clouds.html
[3] ROMANO’S STAR IN M33 - LBV CANDIDATE OR LBV? R. Kurtev et al. 2000.
[4] HST and groundbased observations of the `Hubble-Sandage' variables in M 31 and M 33. Szeifert, T. et al.
Images copyrighted by The Digitized Sky Survey.