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Hi Daryl,
Thanks for pointing that out. It was a mistake I made when updating the meetings/webinars for the first half of this year earlier today. I accidentally unticked a settings that promotes meetings from the events page onto the front page.
Best wishes,
Andy (with my Web Content Editor hat on)
Hi Andrew,
In that case it would be best to create a zip containing everything, or a choice of zip and another compression format.
It is easy to add one or two files, but each file requires its own download page, hence it makes sense to have a single file with everything. It will also be easier for people to download a single file.
Best wishes,
Andy
Hi Andrew,
I agree this sounds useful, thank you.
I may be the person who helps to get these onto the website, so my initial thoughts are about what the files are like. Are there one or many, and what file type are they?
The E&T pages sound like a useful place to put these, although the Drupal software on which the website is based can sometimes make things like this a little tricky. They might need to go in the Publications->Downloads->Sections->E&T area of the website. A backup plan would be to put them on the BAA Spectroscopy Database pages, though the main website would be better as long as it doesn’t get too messy.
Best wishes,
Andy
It is worth noting that while the G magnitudes are excellent, there are known small issues for bright blue stars and faint red stars. Details can be found in Riello et al 2020.
The bright blue stars are G<13 and BP-RP<0.1, appear to have an ‘anomaly’ of up to a few mmags.
The Gaia web pages provide Python to correct the systematic in fainter G magnitudes, G>13. This is not a major problem and in most cases will be very small except for redder stars. For example it can reach about the 1% level for about BP-RP>2, though at the extreme red end can reach 2.5%. I’m using a few million Gaia sources, and in my sample the official correction adjusted 1% of the stars by 1% in G. There is mention in the paper of a separate table in the Gaia archive for corrected G-band photometry, though I’ve not seen that yet and I wonder if it will appear in the coming days.
There also appears to be parallax zero point bias by magnitude, colour and position (Lindegren et al 2020). Again a Python script is provided to calculate this bias.
If anyone is interested in the Python corrections, then the source code can be found on the Gaia webpages here: https://www.cosmos.esa.int/web/gaia/edr3-code
This is not intended to take away anything from the Gaia results, which are amazing. It is usual for a major survey to have some small issues to be aware of, especially noting this is just an interim data release.
Andy
I am glad to see no one was hurt. As sad as it is to loose Arecibo there are huge new projects in radio astronomy. The one that springs to mind is the Square Kilometre Array. I am sure there is a trade off between building and operating new observatories, versus keeping old ones operational.
Andy
Hi Peter,
Many thanks for pointing this out. I did a quick search of recent images and found an idential image by Peter Goodhew FRAS. I have corrected the page as I am sure this was an innocent mistake, possibly even a browser autocomplete when this was promoted to picture of the week.
Our apologies to you and Peter Goodhew FRAS.
Andy
Thanks for sharing this Callum. I heard of this spectrograph a few years ago but didn’t know they were adding automation.
It is great that SX are entering this field though I didn’t see anything that tells me how well the spectrograph performs. The idea looks great, but they really need it in the hands of someone who knows how to produce good quality spectra to see how well it performs in the real world. It could be fantastic but they only showed the most simple of results, a bit like demonstrating a new telescope by taking single images of the Moon without proper processing.
I would want to know how stable is it on the back of a telescope in an imaging run. It appears the design should be very stable but theory and practice don’t always match. I also want to know what the resolution is as that defines what you could use it for, along with how that matches to CCD pixel size. Interesting that the camera can be shifted across the spectrum though I’d want to know how much of a spectrum you can fit in a single exposure, and how stable that movement is. It has to be absolutely rock solid, otherwise things like wavelength calibration and response correction needed to create good quality spectra would fail. If someone could obtain spectra of more challenging targets and do the full end to end process including response correction that would go a long way to demonstrating they have a high quality product.
I do not agree that they are coming in cheaper than their competitors. There are only a couple of modular spectrographs I can think of, most come as complete units. Of the modular spectrographs one is cheaper and the more expensive one is a top end spectrograph designed for large research telescopes. They appear to be coming it at about the same price or possibly more expensive than complete unit spectrographs. That is not to put their spectrograph down, just I did not agree with their comments on the price. This might not be a negative as they have automation, though they are not the only spectrograph with automation capability.
I don’t mean to be too negative as I think SX produce great CCDs and accessories, and I want this to be a great spectrograph. I am just hesitant as this is their first foray into spectroscopy and I’ve not seen any results that demonstrate the quality of the spectra it produces.
Cheers,
Andy
Hi Jack,
I hope you don’t mind but I thought I’d ask what problem it is you are trying to solve.
I remember you were having issues with wavelength shift in your spectrograph. If this is the problem then I don’t think mirror flop in the telescope is likely to be the cause.
Of course if you are having trouble with shifting position of the star when you cross the meridian then that would be fixed by solving mirror flop.
Cheers,
Andy
Hi Jack,
You don’t need high end equipment to do photometry so that should be fine.
What really matters is making sure you do flat fields, and that is the same whatever equipment you use.
Cheers,
Andy
We might be talking about the same thing, but in case not.
You would expect the graph to change once you are outside the linearly region and then into saturation. Once a star becomes saturated you are not detecting all the photons that land on the chip.
Cheers,
Andy
Hi Simon,
The important point is once a pixel is saturated it won’t count any more photons. It is possible that if a tiny number pixels are just above saturation or in the non-linear region then that non-linearity won’t be obvious. There will be lots of pixels contributing. However, it is a risk and you would not be able to justify your result if you were trying to extract a reliable magnitude.
Looking at your graphs, they show a slightly different behaviour in the linear region. It appears to be a steeper slop, followed by a little bit of a wiggle.
If saturation is a problem as you want longer exposures then you can slightly defocus the star. This will spread the photons over more pixels while keeping them within the linear region.
Cheers,
Andy
I can’t offer a perfect way to do this, but you may be helped by looking at this another way.
The photometry aperture containing the light of the supernova will itself contain background light from the host galaxy. That disc containing the light of the supernova will be huge in terms of the galaxy, covering many millions if not billions of stars. Hence the trick is not to subtract a sky background without the galaxy, but to have an annulus that is representative of the background light you are collecting with the supernova photons.
Andy
Hi Mike,
The best way to keep appraised of upcoming webinars is to look at the bottom left of the BAA homepage, where the next 4 meetings/webinars are listed. There is also a full list of meetings and webinars on the BAA meetings/events page.
https://britastro.org/meetings
While the postponed meetings get in the way a bit, the webinars for the next 2 weeks are showing in the bottom left of the homepage.
The next few meetings/webinars are also usually listed in the monthly BAA newsletter. Though with the rapid changes of the past few weeks it has not been possible to know about all of the events sufficiently in advance to get them on to the newsletter, which is why we said to check the events page in the last newsletter.
Sending out bulk emails is a tricky topic. If we send too many we get complaints, and if we send too few we get different complaints, and we have to be careful to keep within data protection regulations.
Best wishes,
Andy
Hi James,
Can you let us know what part of the VSS pages are not working for you, so we can try to replicated the problem? It would also be useful to know which browser and operating system you are using as these behave differently.
I found I had to clear the cache to get the VSS pages working in Chrome, but they worked first time in Firefox and MS Edge.
Thanks,
Andy
The BAA web server was upgraded over the weekend. As Jeremy indicated, I suspect it was some kind of cached data in browsers that needed to be refreshed.
Andy
Thanks for pointing this out Jack.
On a similar topic, the BAA is fortunate to have been given permission to broadcast a webinar for A Special Image for the 30th Anniversary of the launch of the Hubble Space Telescope this Friday 24th April at midday. More details here:
https://britastro.org/node/21425
Andy
Hi Kevin,
Good to hear you are finding worthwhile pursuits during the lockdown. Those are interesting results.
If I am reading those plots correctly, you are seeing a 10%-15% difference at the red end of your instrument response when using either Castor or Regulus. That is quite a substantial difference. Assuming the instrument response from the 2 stars were calculated on the same night and under similar observing conditions, were the altitude of the stars similar? If not then the differing effect of atmospheric extinction with altitude might be the cause, though even then I am surprised by the size.
Another possibility is somehow the slit isn’t being uniformly illuminated by blue to red light. This might happen due to atmospheric dispersion. The atmosphere can start to split the light of a star just like a very weak spectrograph, so you capture more blue or red light depending on where the slit is placed on the stellar source. You could get a similar result with telescopes that contain lenses if they don’t bring red and blue to the same focus.
A way to test for this would be to compare results between a wide and a narrow slit. A very wide slit should capture all of the starlight even if it has been chromatically dispersed by the atmosphere or lenses. While a narrow slit might record more blue or red light as you move from target to target, or across a single target.
Just thoughts, and I’ll be interested to hear what others think.
Assuming there is no reliable way to correct for this, then I agree cropping the spectrum is a good approach.
Keep safe and well,
Andy
According to SIMBAD it is of A2Vn C spectral type. I also found reference to a debris disk in Wikipedia linking to a paper by Wyatt et al 2007 https://arxiv.org/pdf/astro-ph/0703608.pdf.
So it is a main sequence A-type star and the paper quotes an age of 300 Myr, though I think that comes from another paper (I’ve not read the paper in detail, just skimmed a few bits). I am surprised a main sequence star could have a debris disk as I thought this was associated with young stars. If I’ve understood the paper there are collisions in the debris disk generating dust and an IR excess. Perhaps the variation in luminosity is due to variable obscuration by the dust?
Interesting how such a well known and prominent star can throw up surprises to us, well spotted Alan!
Hi Nick,
I remember I had problems parking my Astro-Physics mount with the SkyX, so I wonder if you problems might be related to parking. As the mount doesn’t actually need to be parked I simply slew to a safe position and then turn it off. Of course your pointing problem might be something different but I thought I’d mention it.
Other possibilities to check are whether your location is set to come from the hand controller or the computer.
I’ve never pointed at Polaris as it is not a good star to use for syncing the telescope position. You have good latitude information but the longitude precision is about as bad as it could be as a tiny movement gives a massive shift in longitude.
Good luck, I’m sure you will get there.
Andy
It should be remembered the BAA has not been silent on this matter. Article from last year.
https://britastro.org/node/18560
Andy
