Breath on a Mirror - Astronomy blog by Jaakko Saloranta

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.

Thursday, 21 February 2013

Clouds, polar bears and greetings

Few nights ago I happened to stumble upon the re-opened website of our beloved old geezer Stephen R. Waldee. Steve asked in this January blog entry "... but what's happened to the regular entries by such interesting writers as David Knisely, Steve Coe, Steve Gottlieb, Mark Wagner, my friend Jaakko and several of his colleagues in the frigid north above the arctic circle?"

Finland: Sibelius, Sauna, Sisu and polar bears... wait what?
Courtesy of San Jose Zoo.

I do not know about the rest of the guys, but the winter here in Finland (which is mostly well BELOW the arctic circle) has been the cloudiest in recorded history(?). For example the town of Jyväskylä, in Central Finland has seen only 18 hours of sunshine during the past 2.5 months! So no matter what you try, there's no beating the clouds. The temperatures, observing conditions in general and cloudy days are something most people living in Central/Southern Europe / US cannot even fathom. The thought of planning an observing session for tonight/tomorrow, is something we're not familiar with. With the weather patterns in here, clouds will always sneak up on you. Not to mention the general changes in weather even I've witnessed over the past few decades: more clouds, warmer temperatures and simply crappy winters in general. So if you want to start astronomy, do it somewhere else than in Finland!

NGC 55

Despite the cold spell on the homepage front, many things have been going on. I still have a huge pile of sketches to be scanned and processed from my trip to the US as well as Tenerife. Here's an example: NGC 55 sketched with a 4.7 inch scope @ 90x (45') from Boca Tauce, Tenerife, Spain (2034 meters / 6673 feet) on 23rd of November 2011. The description reads: "A gorgeous sight. Huge, WNW-ESE elongated galaxy with a mottled appearance. NW part of the galaxy contains a bright, elongated nucleus with somewhat mottled appearance. Two brightenings visible within the halo. Larger and brighter knot appears as slightly NW-SE elongated. The smaller and fainter knot appears as a nearly stellar, roundish spot in the E side of the galaxy's halo with a faint 14th magnitude star just W of it. A darker void seems to separate these two possible HII-regions from each other. Several 10-14th magnitude stars in vicinity / within the halo. Size 20' x 4'. With low power the galaxy is visible in the same field of view with pointy rock formations of Las Cañadas caldera."

Between this post and the latest entry from less than year ago a lot has been going on behind the scenes. I've managed to contribute several sketches to the Las Vegas Astronomy Society's (LVAS) "Observer's Challenge". Four of my "Deep Sky"-columns have been published:

Tähdet & Avaruus 8/2012

Hunting the invisible: Cygnus X-1 (Tähdet & Avaruus 4/2012)
The Prince of Darkness - E. E. Barnard (Tähdet & Avaruus 6/2012)
Colors, details... oh my - Going against the Hubble Space Telescope (Tähdet & Avaruus 8/2012)
Fifteen years of astronomy - The fondest memories (Tähdet & Avaruus 2/2013)

The "night sky" in Tapanila, Helsinki

So although it might seem bad on the outside, I'm still alive and breathing. This past year has brought many life changing things to my life. The one with the biggest impact was moving from the outskirts of Vantaa to rural Helsinki. The drop in SQM-L readings, limiting magnitude and huge increase in light pollution has had a really negative impact on my hobby. Not to mention living on the 3rd floor. Trust me, when the SQM-L readings drop below 18, that's when everything that's fun and worthy in observing - dies. When the snow melts away in a month or so, I'll probably try to do some observing before the summer break. One thing I've changed in my sketching is the speed. I've started to spend even more time on a single object than usual and it is starting to pay off. Simply put: more vague details than ever! And Steve, I'm sure you still have my email address. If you don't, you can see it if you're reading this. Use it buddy!

Saturday, 28 April 2012

Cosmic Challenge by Philip S. Harrington - A review

Cosmic Challenge - The Ultimate Observing List for Amateurs by Philip S. Harrington
Cambridge University Press (November 30, 2010)
ISBN: 9780521899369
466 (true) pages

Rating: 8/10 - Recommended

The ultimate observing list for amateurs. With such a name for a book you're entitled to some serious challenges from the night sky. I have to admit, I wasn't sure about getting this book. The main reason was, that I don't like digital sketches and I knew Philip's are digitally made. For me, such sketches easily spoil any book, article or anything they're associated with. Using, say Adobe Photoshop might let you do all the work with a computer but even a simple diffuse, nebulous glow is something that a computer cannot do properly without making it look otherworldly. And digital sketches hardly represent the true eyepiece view - this is the main reason why I dislike them.

So how are the sketches in the book? Well, surprisingly good. There are some bad apples to my eye in the bunch such as: M57 and NGC 7331 to name a few. The biggest problem by far in the book is that the most of the sketches are so low contrast that you actually have to us averted vision to spot them! I understand this is to represent the difficulty of the objects and how they even can look at the eyepiece but contrast up man! This issue was already discussed in CloudyNights.com but I was surprised at how obvious it was. Also, the accuracy of star placement in some of sketches is staggering to a point I wonder if they've been actually done to a printed starfields? I'm not saying such accuracy is impossible to achieve - it would just literally take hours. Most of the drawings have very, very high accuracy but some have some misplacement here and there but this is rare. So I suppose the original sketches are handmade.

What of the actual challenges? You can, of course, have many thoughts about them. I love the fact that there are so many of them and more importantly for all apertures! What a great idea to have some naked eye challenges for a start! I would have liked to see sketches of them too which sadly are missing.

I personally would have changed several objects to different telescope categories but this isn't MY book is it. I'm glad there are some real challenges (although a bit too obvious ones) for monster telescopes (15 inch aperture and larger) such as Einstein's Cross, Hickson 50, Seyfert's Sextet and so on. From my point of view, some of the monster telescope challenges should be in large telescope challenges instead (10- to 14 inch telescope). Such objects are Leo I, IC 1613, (brightest of) M31 globulars, Terzan 7, WLM, Simeis 147 are most certainly small telescope challenges (although being difficult with larger ones as well). For example the author speaks of how difficult it is to observe the entire Simeis 147 at once in the narrow fields of view of large aperture telescopes. Could there be a better place for a high quality, wide field refractor than this? No! Especially considering that there are many observations of the object seen only with apertures around 4 inches! Some other that did hit the eye were galaxies beyond M44 (if you remember, Steve Waldee has seen all of these listed in the book with his 10 inch telescope!), Copeland's Septet, PK 164+31.1 (both visible with 8 inch aperture) and several other galaxies and groups should at least be downgraded to the "large telescope challenges" for sure. But most of the "bad" things in the book can be discarded as matter of opinion and personal taste. Other little things I noted (desperately grasped on) include:

If you see M13 (non stellar, 5.7 magnitude object) with the naked eye - your naked-eye limiting magnitude can't be 5.5 but is more likely 5.9 at least.
Seeing M33 with the naked eye doesn't really need "absolutely, perfectly pristine skies". It is actually quite easy to see even from Finland which isn't even remotely absolutely, perfectly pristine anything.
Chart 5.19 IC 10 (page 264) says "Sculptor". It probably should read "Cassiopeia".

If you want something simple and short, here it is: the book is simple (in a good way), easy to navigate and the charts are most excellent. It is well written and while some might argue the text portions are a bit on the short side, I don't find this a problem but actually a bit of a relief (after reading O'Meara). Despite my - at first - biased view of it, the book is far from bad. It is quite excellent and I would recommend it to... well every amateur astronomer out there. And good to see my friends and colleges Timo and Steve mentioned in the book as well. I'm looking forward to volume 2.

8/10 for every living soul - Recommended

Friday, 13 April 2012

5 curious and nearly unknown nebulae for photographers

Have you already taken a photo of every Messier object in the sky - twice?
Nothing in MegaStar that you haven't already photographed?
Looking for something different? Here's your chance!