[Dr Paul Leyland]

When I first saw your post I thought that 500mm was the aperture, not the focal length!

[Dr Paul Leyland]

I’m trying to orientate myself.  To make things easier, could you say (a) whether shorter wavelengths are to the left or the right of the image as shown here and (b) are the lighter colours bright emission lines (i.e. it’s a positive image) or dark absorption lines on a negative continuum?

I’m almost certain that its the first in case (b) but it would be good to have it from the horse’s mouth as it were.

[Dr Paul Leyland]

I can see a few images of Landolt fields being taken when I’m next back in La Palma.  Let’s see, I’ve RGB&Luminance filters, pretty pictures for the taking of (and which I’ve used precisely once, on M57, just to see whether they work); Johnson-V which is by far the most used for VS work; Sloan g, r and i (only ever used the second for production work, though i was once used as an experiment to see whether it improved contrast of Jovian surface features).  A “H-alpha + continuum” is in there too, but it’s never been used because I’m not interested in either visual work or in taking pretty pictures of H-II regions.  Two slots are empty — one will remain that way and I’m tempted to get a Star Analyser SA200 to play with.

Any suggestions as to what other photometric filters may be worth purchasing, possibly part-funded by selling off the ones I don’t use?

[Dr Paul Leyland]

That is also my belief.  Unfiltered magnitudes also correlate very well indeed with Gaia-G magnitudes.  This should come as no great surprise …

That’s why I generally quote Gaia-G magnitudes for objects on unfiltered images I’ve taken.  Please note, these are NOT images taken for photometric analysis, for which I almost always use V or Sloan r filters.

[Dr Paul Leyland]

Further to Jeremy’s comment: the use of dark and flat frames goes a long way to to cleaning your image of truly hot and cold pixels.  However, it cannot deal with either cosmic ray hits or satellite trails close to the VS or a comparison.  If you see any anomalously faint or bright estimate, take a close look at the corresponding image to see if there is an obvious reason to reject it.

In my case, I throw away perhaps two estimates per thousand.  It’s only when processing thousands of images does it become really noticeable.

[Dr Paul Leyland]

Thanks.  That’s where I just found it but I’m quite certain that it wasn’t there when I posted yesterday — it was the first place I looked, not least because that was the destination of the link in the email sent to me.

The forum page also now shows the Oct 2019 issue; it did not yeterday.

Oh well, it all worked out in the end.

[Dr Paul Leyland]

8<-------------------------------------------------------------------------------------------->8
On Tue, 2019-10-08 at 21:21 +0000, BAA electronic bulletins wrote:

The BAA’s latest newsletter
View this email in your browser

BAA October Journal now available on line

How quickly the longer chillier evenings have come around. It seems
…
course, after the July eclipse, which many BAA members viewed, Nick
James personal account makes good reading. He is still collecting
eclipse images and videos for the BAA Eclipse 2019 DVD. If you would
like your images to be included please send them directly to
solareclipse@britastro.org
8<-------------------------------------------------------------------------------------------->8

The first bit specifically states that the October Journal is available on line. The second quoted portion only makes sense if it refers to the 2019 issue.

I still can’t find the October 2019 issue anywhere 8-(

[Dr Paul Leyland]

Despite the mail announcing its availability I’ve been unable to download it.  I contact the Reply-To: address to ask for assistance.

Paul

[Dr Paul Leyland]

Nice!

[Dr Paul Leyland]

First off, I’ve verified my stacking code does the Right Thing by digging out some old images of (532) Herculina where it is by far the brightest object in the field and so there’s no chance of missing it.

To answer your question, the (slightly abridged) MPC ephemeris for Leda gives
Date UT R.A. (J2000) Decl.
2019 06 26 000000 17 02 01.7 -22 07 28
2019 06 26 001500 17 02 01.4 -22 07 27
2019 06 26 003000 17 02 01.1 -22 07 26
2019 06 26 004500 17 02 00.9 -22 07 25
2019 06 26 010000 17 02 00.6 -22 07 25
2019 06 26 011500 17 02 00.3 -22 07 24

and my subs were taken between 2019-06-26T00:20:10 and 2019-06-26T01:12:21 inclusive, with a mid-point of 00:46:15.
The brightest pixel in the indicated blob lies at 17:02:01.3 -22:07:26 according to the ds9 viewer.

Good agreement, in other words, especially as the plate scale is 1.42 arcsec/pixel..

You are much more experienced at this sort of thing than I — it’s my first attempt — so how much credence would you place on the identification?

It’s pretty clear that when I next attempt to image Leda I should aim for a much longer total exposure time.

[Dr Paul Leyland]

Here’s the stack I made.  The red arrow might, just might, indicate Leda but I’m far from convinced.  It’s in about the right place and it’s not trailed like the other stars.  Unfortunately, it also looks like it may be noise.

[Dr Paul Leyland]

How do I delete a duplicate post made in error?

[Dr Paul Leyland]

I’ve long had them all installed.  The problems lies in the version mis-matches.  The latest tarball still tries to link against versions which are not on my system, they being either newer or older.

I’m quite willing to keep the sources secret if you wish, even though my own code is almost always released under a BSD-like license.

[Dr Paul Leyland]

Minor problem. Your tarball contains dynamically linked binaries which link against versions of libraries not installed on this Ubuntu system. For instance:

pcl@thoth:~/Nick$ ./fcombine
./fcombine: error while loading shared libraries: libnetpbm.so.11: cannot open shared object file: No such file or directory
pcl@thoth:~/Nick$ locate libnetpbm
/usr/lib/libnetpbm.so.10
/usr/lib/libnetpbm.so.10.0
/usr/share/doc/libnetpbm10
/usr/share/doc/libnetpbm10/changelog.Debian.gz
/usr/share/doc/libnetpbm10/copyright
/var/lib/dpkg/info/libnetpbm10.list
/var/lib/dpkg/info/libnetpbm10.md5sums
/var/lib/dpkg/info/libnetpbm10.shlibs
/var/lib/dpkg/info/libnetpbm10.triggers

Likewise, my libwcs is in /usr/lib/x86_64-linux-gnu/libwcs.so.6 whereas the binary calls for libwcs.so.5

Would it be possible to have either source code (preferable) or statically linked binaries please?

Thanks.

[Dr Paul Leyland]

Thanks Nick, this sounds very much like what I’m looking for.  As for using the CLI, that’s what I generally do anyway.

This morning I kludged up a Perl script to modify the CRVAL[12] cards in the FITS headers in attempt to persuade SWarp to  stack the images with an offset.  Not very successful though.  Ether I screwed up the code or the total exposure just wasn’t long enough because I can’t see anything circular on the stacked image — just lots of trailed stars.

[Dr Paul Leyland]

Good point.  I knew I was missing something.

[Dr Paul Leyland]

1/32K difference in flux corresponds to a roughly 1/32 millimag dip in brightness.  Either I’m missing something important, which I do quite often, or I’d change “tough” into “a chance somewhere between nil and negligible”.  That said, I’m a great fan of understatement.

In the ARPS meeting today we were advised, correctly in my opinion, to concentrate on objects with a transit depth of at least 10 millimags.  Three hundred times deeper, in other words.

My experience is that good observations of a transit depth of, say, 5 millimags is achievable but not entirely trivial.  I couldn’t manage one millimag.

[Dr Paul Leyland]

The optical variability is measurable by amateurs.  I was paying attention to your “visual or CCD” request, honest!

See http://www.threehillsobservatory.co.uk/astro/astro_image_33.htm for instance, where Robin Leadbetter presents his images and http://www.threehillsobservatory.co.uk/astro/pulsar_detection_1.htm where the technique is described.

[Dr Paul Leyland]

CM Tauri, at 33.5 milliseconds, is an obvious contender.

[Dr Paul Leyland]

I’d expect more to come from the hemisphere around the solar apex but we’re going to be in the small number statistics regime for a long time yet.  Even if interstellar objects are found annually it will be a few decades before the statistics are good enough to make a definitive statement.

I see very little chance of determining their original star.  Unless they were ejected very recently from a very close neighbour the perturbations from other stars will make the trajectory very curvy.  It takes a long time to travel anywhere at only 30km/s (chosen because it make the arithmetic easier — it is 0.0001c).  At that speed it takes over 3 million years to travel 100 parsecs — close by in galactic terms.

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