Forum Replies Created
-
Posts
-
Hi Tony
Yep they are Relco 480 starters, though I believe Shelyak sort them, probably based on trigger voltage. Their power supply is also designed to prolong their life (constant current ?)
I have some notes on this that Francois Cochard published somewhere. I will dig them out
Cheers
Robin
Francois Teyssier on the ARAS forum is a good amateur contact for information on spectroscopy of symbiotics. He produces a regular Eruptive Stars Spectroscopy Newletter which includes regular comentaries by Prof Steve Shore and is now listed on ADS, unusual for an independent amateur publication
http://www.spectro-aras.com/forum/viewtopic.php?f=33&t=2254
Back issues are also available here
http://www.astrosurf.com/aras/novae/InformationLetter/InformationLetter.html
Cheers
Robin
Hi Kevin,
With the manual dispersion function in ISIS you double click either side of each line in the uncalibrated (combo) spectrum and ISIS calculates the exact pixel position of the centroid of the line and enters the value in the table. You have to tell it to look for either an emission or absorption line within the two clicked positions though (buttons at the top of the window) so you would need to click “absorption” before measuring the water line positions and “emission” before measuring a lamp line.
Yes, if you set the reference line to 0,0 it just uses the predefined dispersion equation but if your dispersion was measured on a reference star with the telescope pointing in a different direction to the target, this can be out by a constant shift due to flexure so adding a reference point using a lamp spectrum corresponding to the target will correct for this. (correcting the constant in the polynomial)
Robin
Hi Kevin,
It should work ok provided you don’t see any fixed offset between water and lamp lines. (You would see this for example at H alpha if you always need to make a consistent correction using the water lines.). Don’t forget to switch between absorption and emission for the specific line you are measuring in the dispersion calculation tab. I would suggest calculating the dispersion just on the reference star where the SNR in the water lines is likely to be higher and then using this calculated dispersion on the target with one of the neon lines as a reference point to correct for any flexure offsets.
Alternatively have you tried a long exposure with the Ne lamp to see if you can see any weak Ar lines to use instead of the Ne lines? (I could see some with my Ne lamp but they are more obvious now I have upgraded to the NeAr lamp)
Cheers
Robin
Note that the dedicated 1:1 duplicators designed for use with full frame SLR will crop slides when used with DSLR with smaller sensors so you might need to modify them eg with an extension tube. I think you can get versions with 0.6 reduction for DSLR though
If you have a digital camera with a macro lens you could rig up something like this.
https://www.scantips.com/g4/p1230510.jpg
from this page
https://www.scantips.com/es-1.html
I have used this sort of setup in the past using the sky as a light source and a cardboard tube to keep the light out but the results depend on the quality of the lens (Star fields tend to show up any deficiencies, like pincushion etc)
Cheers
Robin
I see today that S&T prefers Godzillas
https://www.skyandtelescope.com/astronomy-news/pluto-charon-missing-small-craters
Robin
Note that although an early spectrum of sn2019np was taken by the Li-Jiang telescope, the official confirming spectrum was actually taken several hours earlier using Faulkes Telescope North and uploaded to the Transient Name Server (As it happens 4 minutes before the Atel #12374 was issued, though since 2016 the TNS has been the official IAU system for recording supernova discoveries and confirmation)
https://wis-tns.weizmann.ac.il/object/2019np
There are also three amateur spectra of this SN in the BAA Spectroscopic database
and more spectra on the ARAS forum here covering the evolution up to currently 17th Feb
http://www.spectro-aras.com/forum/viewtopic.php?f=38&t=2205
Cheers
Robin
Another spectrum last night. It has cooled significantly (to ~15000K) and the Balmer absorption lines are more pronounced
Robin
Hi David,
I’m afraid I am not enough of an expert to interpret spectra of CVs, beyond being able to tell the difference between the spectrum of a classical nova and one of a dwarf nova. This is a typical spectrum of a dwarf nova in outburst. In this case a large amplitude outburst of a star with no previous history of outbursts so a likely WZ Sge (UGWZ) type (I am reliant on Patrick Schmeer for this classification)
The source of the additional flux is impressively hot. The continuum fits to a ~35000K Planck curve, like an O star
Robin
I’ve just seen there is now a revision to the path noted at the bottom of the page. (The original track was calculated based on the position of the centre of mass of the A-B system rather than Sirius A !
I hope you have not already made your travel plans !
Robin
Just spotted this on the S&T website
https://www.skyandtelescope.com/observing/will-sirius-disappear
“Monday night, February 18th. That evening around 10:30 p.m. MST (5:30 UT February 19th), there’s a good probability that the 17th-magnitude 4388 Jürgenstock will occult the sky’s brightest star for up to 1.8 seconds.”
The event is not visible from the UK but anyone on the narrow path though North America could get (very a brief) view of Sirius B free from the glare of its bright companion. (Sirius is predicted to be totally eclipsed for just 0.2sec !)
Robin
I’ve not done any scientific measurements but when I made mine I read that most dew shields are too made short and they should be 3x the aperture. This does look rather long though and gives problems with the mount in a breeze.
I first saw the newspaper trick on a small refractor at a sky party in Denmark. Most people who did not have heaters were struggling with dew but not this guy. (I think perhaps he changed it once during the night when it got too soggy)
Robin
As an aside, dew is less of a problem in breezy conditions as the airflow is constantly removing the cooling boundary layer of air over the surface where dew is forming. (Which is just as well as my dew shield acts as a sail !)
Dew forms on a surface when the temperature of that surface falls below the dew point. A surface exposed to the clear night sky cools by radiating heat out into space which is only a few degrees K (This is an over simplification of course as the atmosphere blocks the radiation at some wavelengths but you get the idea). A dew shield works by limiting the angle over which the heat can be radiated away. Cooling still takes place but more slowly. There may be other effects. For example some people swear by rolled up newspaper or other absorbing material which perhaps preferentially absorbs the moisture in the air close to the optics.
Cheers
Robin
Hi Eric,
If you were transmitting you might want to tune it more precisely to provide a better match to the transmitter but a 3 element yagi antenna tuned for 144-148MHz should work ok at 143MHz for receiving. (It would be difficult to retune in any case as you would need to increase the length of the elements slightly). For example there is an article on the BAA radio astronomy website showing a 7 element yagi centred on 143 MHz with a flat response over +-7MHz bandwidth, fig 2.9 on page 8 here
https://www.britastro.org/radio/projects/Antennas_for_meteor_radar.pdf
Robin
Hi Eric,
Is this specifically using the Graves transmitter on 143MHz ? If so a small 2m amateur band yagi could be a good choice. Like these perhaps
https://www.radioworld.co.uk/hygain-2m-3-el-beam-500w—vb-23fm
https://hamradiostore.co.uk/cushcraft-a148-3s.html
Cheers
Robin
Hi George,
The fits file is 2 column data table (wavelength and flux) not an image so Maxim does not understand it. You can view the data in a free general fits data viewer like NASA’s fv for example or alternatively download the dat file version and view it in notepad, excel etc. Better though is to view it in a free dedicated spectroscopy program like Visual Spec or ISIS etc. I have also loaded it into the BAA spectroscopy database so you can view it there too.
https://britastro.org/specdb/data_graph.php?obs_id=3607
Cheers
Robin
