coatesg

Well, part of it is governed by Poisson statistics and the inherent shot noise arising from the star's signal and the background, and thermal + read noise contributions. 

I think the plot above is considering the first two largely. The BAA spreadsheet also takes into account the error in reference star magnitudes as I understand it.

Error bars of the order of about 20 mmag are about the best I get too. To get better, expose for longer (avoiding saturation), go somewhere darker (though may not make a huge difference for bright objects) or stack images (which is not ideal for some time resolved work).

Looking good - the SXPhe and HADS type stars are all good targets on this type of timeframe - it's satisfying to get a useful result over such a short timeframe. Some are also a fair few mags brighter than +14.

Worth also checking out nova/dwarf nova and looking at accretion disc rotation periods (often of order ~0.1d). Often best at outburst.

I found this in our loft when getting the Xmas decorations down - I'd been stung twice by queens in November, and dispatched another 16 in the house - couldn't figure where they were coming from until this point and didn't know it was there in the summer at all. Poor santa..

A 3 foot wasp nest makes for a good show and tell for the kids at school though!

22 minutes ago, JamesF said:

 The smooth round-ish object about 50mm across in the last two photos looks like a wasp nest that was abandoned, possibly because the rest looks like a pretty big hornet's nest.

No wonder I've seen so many of them around last year and this...

 

Oof! I just have issues with wax moth around my frame storage - luckily not this! Been a good year for my bees so far, had 17lbs of early spring honey off one hive (which has set quickly as rape seed in there), they have 2 mostly full supers now as well, and have had to do anti-swarm procedures twice already... Also caught a swarm (not mine!) last weekend, so rapidly running out of boxes, frames, space etc...!

On 19/05/2019 at 22:26, Jkulin said:

My wife called to me last week as there was a massive bee/wasp in the lounge, indeed it was big, but I don't know if it was a hornet or a queen, any ideas?

That's definitely Vespa crabro, the European Hornet (our native one) - the head markings and yellow down the abdomen give it away. They are enormous, impressive beasts!

(The invasive Asian one is smaller, much darker on the abdomen, and has yellow lower legs).

On 20/05/2019 at 11:47, carastro said:

Very interesting James, thanks for that.   

I knew about the poison sac left behind and how it works.  I got stung camping once as unbeknowing we had pitched not far from a hive of wild bees/hornets!!!  Boy that was painful and I was yelling at hubby and our friend to get me some tweezers so I could get it out.  Friend presented me with a pair of pliers which I knew would simply squeeze the poison in,  In the end I managed to get it out using a hairgrip which fitted underneath the poison sac.  

Carole 

Credit card works really well - use it like a knife to quickly go across the skin surface to get the barb out without squeezing it all in!

Another HADS star from last night, V467 Dra - this one has a period of 4.74hrs, so I let the scope chug away. Guiding was working really well as well.

This is from 369 separate 30sec exposures over almost 5hrs, through 350mm f4.6 newt, V filter, ST2000XM. Transparency not so great and the y-axis is quite expanded compared to some other HADS plots as there's only 0.35 mags variation for this one.

8 hours ago, Lockie said:

The UK used to have a 28" Victorian refractor at Greenwich, but sadly it's no longer in use.  I wonder if there is a larger refractor then our clubs 10" / 258mm Tomline refractor in use anywhere in the UK? 

 

Yes. The Northumberland at Cambridge is very much in use (12" something like f20...) - the University AS and CAA use it.

When I studied there I used it a bit, but always preferred the rather good 8" f14 Cooke refractor (The Thorrowgood) next door...

(Had a feeling the 28" at Greenwich is still used though)

Well, the biggest might have been the INT, before that departed to La Palma. The 36" at Cambridge (https://www.ast.cam.ac.uk/about/36-inch.telescope) is optical, and still in use for research on double stars IIRC - Edinburgh looks also to have a 0.9m Cassegrain (36") but (according to the wikipedia page) is no longer in use. (?)

The 36" Yapp at Herstmonceaux also ties I think, but the 38" Congo at Herstmonceaux beats them all (though don't believe it is in use, and never had been, as the optics were rubbish...)

I would guess Lord Ross' Levaithan at Parsonstown is probably the largest in the British Isles (but not the UK as it's in the Republic of Ireland) - 72"/1.8m!

If I've been short of comparison stars, for a quick analysis I've looked at using the stars in the AAVSO APASS catalogue (you can access the data really easily by using Simbad). When I've requested an "official" sequence via the AAVSO process, they've used the same data.

Though, I did manage to request a set of comparison stars recently, where there was nothing usable above 14th magnitude in the FOV (I had a shade under 30' like Dave) - the errors in the brighter comparison stars were up to 20% of the range of the variable itself ? - exception made to use them as the data can be adjusted later if the comparison stars are improved by a subsequent survey. (It makes no difference for timing studies, but for getting absolute magnitudes it does somewhat!). 

Depends a little bit on how good your guiding is I think - do you have any details on the ability of the HEQ5 to guide successfully? I say this, as it gets increasingly hard to guide at longer focal length, though a catadioptric is probably easier than a longer tube scope like a newt (less moment of inertia).  

If the mount is up to it, then a Newtonian would be possibly the cheapest way forward I think in terms of price vs aperture - you will need to learn to collimate though (it's not too hard once you've done it a few times - it takes me longer to take out the camera, and reconnect it afterwards than the actual collimation these days). Having a perm setup also helps enormously. 

(Odd it came out as a double line though - suspect possibly a debayering artifact?)

Assuming the image was captured sometime over 2300hrs on 2018-01-01, there's only two possibles that an MPC search (https://minorplanetcenter.net/cgi-bin/checkmp.cgi) around 6 arcmin comes up with - 2013 YD60 (426964), or Luisa (599). The former is mag 21.something, the latter mag 12.something so with that, and manually looking at the ephemeris and moving a mouse around to see where the RA/Dec is, my guess is that it is Luisa. 

A single sub with date/location would pin it down exactly.

Lovely image - it's very natural and has a real 3D effect to it. LBN785/Ced31 (to the left) looks like an interesting target for a close-up too. 

Thanks for the kind words all

I really do like imaging with this combo. 

I grabbed 3h40m of the Sadr region stretching from the crescent up to NGC6914 (not visible as it's a reflection neb!), in HA light - may add to this in HA, but also would be nice to bring LRGB into it at a later date. 

QHY163M, Canon 200mm 2.8L II (working at f3.85), Losmandy GM8 - taken 17th Sept 2018, West Oxfordshire. All in 5min subs, guided with a ASI120MM on a 50mm guider. Baader 7nm filter. Processed in PI.

Thanks for looking.

(ergh - jpg compression artifacts aren't great in this 

Looks good - Just wonder if there is more there to be pulled out - perhaps leaving the background lighter would help to show the fainter reaches? Also, maybe masking the core while processing would stop the details near to the centre blowing out a bit.

Always errors - even Messier had a couple of errors...

Catalogues will also always vary in values (eg comparing Sh2 to NGC/IC will always give slightly different values for the same object) - the VizieR catalogues are (should be!) straight copies of catalogues from papers and they have the publication reference in the search results. You'll also find that a lot of deep amateur images show a lot more than professional catalogues indicate.

Remember as well, if the paper is reasonably old, the original coords will be in J1950, so that's why you need the J2000 coords to account for precession.

(Also note, diameter isn't a required field - it produces a cross on the annotation if null)

7 minutes ago, swag72 said:

How did you get the diameters on the LDN catalogue as I can't see it in Vizier ?

Ha! I think I converted the square area in degrees to a diameter  (Not that accurate, but probably close enough).

As I said, old catalogues are quite inconsistent!! ?

1 hour ago, swag72 said:

@coatesg - Mmmm... I've come up with some interesting quirks!!! But I hope I can work around them somehow

Let us know if you hit a block and we'll see if we can work round it! The catalogues aren't always consistent, and that can cause a hiccup or two.

Hints/Notes:

There are instances where the catalogue isn't present in VizieR -  mainly older obscure catalogues - I offer the Bernes catalogue (Bernes, 1977) as an example here. Bernes 100 (written in Aladin/CDS speak as: "[B77] 100") is a small bright neb just to the north of M78. In these instances, you might be able to find it in a separate catalogue, or if not (as in Bernes 100!) just be better off making the data file by hand! This is equally the case if there's only a couple of items you want to add onto the image. You can look up the items by loading a Simbad layer in Aladin - this allows you to click on known items and get the details you need. In Aladin desktop, this is available under the tree on the left under Collections > Database. 

Note that catalogues get added into VizieR on a regular basis as long as the catalogue is in a standard format. Details are in the news items on the VizieR homepage: http://vizier.u-strasbg.fr/vizier/index.gml

=====

If the image fails to solve (or you have a non-linear version that won't solve for example - I had this problem with a processed version of the Coathanger; the non-linear nature appears to upset the star matching algorithms in use). In this instance, check your parameters first - the closer the params, the easier the solve is.

If this still fails, you could try doing a solve on a linear version of the image, and then transfer the coordinates using the DynamicAlignment process, followed by the ManualImageSolver script in Pixinsight. The PI documentation is quite good for this: https://pixinsight.com/doc/scripts/ManualImageSolver/ManualImageSolver.html . The first stage is to solve the linear image. Then start DynamicAlignment - choose the solved image as source, with the other image as target. Then, if the geometry is the same/similar, clicking on source stars all over the source image should produce matching stars in the target. Choose tens of stars all over the image, and then drag the DynamicAlignment window onto the desktop to make a process icon for the alignment. After this, fire up the Manual Solver script and, choosing the linear image as the source, and the icon you created as the Control Points Icon, you can get PI to apply a solution across from one image to another. This should then allow Annotate to run. 

Hope this has all helped!

So by this stage, we should have a tab separated file with the catalogue we want to include in the annotate script. 

To add this catalogue into the Annotate script, we use the "+" button on the Annotate script window, and then choose "Custom Catalogue" towards the bottom of the list in the Add Layer dialog.

Once the "Custom Catalog" option is selected and added, you have to then choose the Catalog Path (where you saved the tab separated txt file), set the colours, and then hit OK again to re-run the annotation using the new catalog.

With the final result (note the two LBN objects):

And that's the basics of obtaining a custom catalogue from VizieR and using it - here's a few catalogues I've already made:

Lynd's Bright Nebulae : lbn.txt
Lynd's Dark Nebulae: ldn.txt
Bologna Catalogue of M31 Globular clusters: revised_bologna.txt

Quite often, you'd like to use the Annotate script to use custom catalogues to annotate your images. If you can't find the catalogue to download online, then you can make your own for use in the script. The script uses tab separated files with the following headers:

RA
DEC
NAME
DIAMETER

RA and DEC are set in the file as decimal values - RA going from 0 to 360, DEC from 90 to -90. NAME is freetext (and what is used in the annotation), and the DIAMETER is in arcmin.

If you only have a couple of objects you want to add onto an image, you can create the file by hand - here is an example of a file as viewed in Notepad++ (with the tabs visible in the file to make it clear how the file is constructed):

You might feel that copying this out for large catalogues is beyond your patience in data entry (!) - at this point, we need a way of downloading and manipulating the data on a computer. Here, I'm going to use the web site "VizieR" (http://vizier.u-strasbg.fr/viz-bin/VizieR) to grab a catalogue in computer format to allow me to get it into PI. 

VizieR has what appears to be a rather complicated interface, but you simply need to search for the catalogue you are after - most of the time, the prefix is fairly easy to sort out - here I'm searching for the LBN (Lynd's Bright Nebula) catalogue. The search feature will also search for Author as a keyword:

Hitting "Find..." results in the following result:

From this screen we can choose what information we'd like to return from the search. We don't need to return all the columns to be sufficient to feed Annotate. VixieR will calculate RA/Dec coordinates in J2000 epoch from the data in the catalogue (here the catalogue is in J1950 epoch, so this is very handy...) - the checkbox for this is in Preferences on the left and set by default. From the main section, we need to deselect everything and then select "Seq" (Running number) and "Diam1" (Largest dimension - already in arcmin). Make sure you change the Dropdowns in preferences to "ascii text plain" (to force text output rather than a web page), and set "max:" to "Unlimited" once you're happy you have the correct parameters [NB: I have a feeling there is a hard limit on the size of result set that can be returned - there's something in the VizieR FAQ about this - I've not hit it yet myself....]. Also ensure the position is calculated in decimal using the option at the bottom of the Preferences box. 

[NB: it may not always be this easy - sometimes the diameter is missing (this is OK for the annotations  as it produces a cross) or you have something else like diameter so you'll have to convert.)]

Result is as follows:

From here, we need just the data in the table after the headers - copying this out into a text file is sufficient to allow its import into Excel using the option to import delimited data (with a space as the delimiter). At this point, we need to add the headers into the file as per the file example above, and add the catalogue prefix onto the data in the Seq (ie the NAME) column.  Here's an example of the file in excel after the fiddling around with the name column (HINT: the CONCATENATE() function is useful here). 

The final step here is to save the file in the right format - Excel does it fo you by choosing "Text (Tab delimited)" as the format option in the save as dialog:

Next up is how to use the custom catalogues.

At @swag72's request, I'm putting together a quick guide as to how to use the Pixinsight annotate script, including how to produce and use custom catalogues.  [Mods - please feel free to move as needed if this isn't the right place to put this!]

I'll use an image to demonstrate this - this is the (unprocessed!) L channel from an image of the region containing and to the north of the Coathanger. First step is to solve the image - most of the time, this is simple to do using the Image Solver script. 

The Image Solver needs some initial coordinates to setup the search. You can search for the image coordinates using the Search function if they aren't already set - if they are being dragged through from the image (eg from SGP) they will already be populated (or at least be close). The coordinates don't need to be accurate, but the closer the better - at the least, make sure the image contains the seed coordinates. Here, I've searched for "Collinder 399" and it returns the coordinates of the Coathanger (at the bottom of the image). Set the focal length, pixel size, and hit OK - you shouldn't need to change params unless it fails to solve (beyond the scope of this guide!). 

If it all goes OK, then you'll get a set of coordinates, image size displayed in the Process Console. (HINT: It's sometimes easier to solve a linear image if a non-linear refuses to solve).

At this point, the image has a solution, and it will be retained as long as you don't crop, rotate, scale, resize, etc the image. (it'll warn you if the action you are performing will affect the solution). 

At this point, we can move onto the annotation. 

The default settings for the Annotate script (Script > Render) are shown - this is a very simple set of parameters (though, the NamedStars and Tycho catalogues will result in a very busy annotated image!!). 

The options available for each of the catalogues allows the user to set options such as the colour of the marker/text, the size of the text and the relative position of the text with regards to the centre of the object. 

The user can also choose to include other catalogues in the routine - there are quite a few catalogues available to the user by default - these can be found by using the "+" button below the "Layers" list of catalogues:

At this point, hitting "OK" is usually good enough to get an annotated image produced - the result of using the script with the VdB and Sharpless catalogues added, and with the Tycho/Named stars catalogues off. 

Next up is how to create new catalogues for more obscure targets....