robin_astro

The problem is stars are not black bodies, the effective temperature Teff is not the temperature of the star and the relationship between B-V and Teff is an empirical not theoretical one Robin

Imaging the crab nebula and pulsar through a synchronised shutter was good fun though http://www.threehillsobservatory.co.uk/astro/astro_image_33.htm

For Hipparchus read Hipparcos everywhere 😉

You have misunderstood where the ability of Gaia to measure a larger number of parallaxes measurable by Gaia comes from. While it is true that Gaia can measure fainter objects, the main advantage of Gaia over Hipparchus is due to its ability to measure parallax to greater precision hence also extending the rage to smaller parallaxes (greater distances). This is mostly due to technological advances, not the increase in aperture (For example Gaia uses wide field CCD cameras allowing direct measurements of angles between objects whereas Hipparchus had to measure each object independently) Cheers Robin

Not really. You just need a statistically valid sample and knowledge of stellar populations. Robin

Isn't Gaia distance measurement limited by the precision to which the parallax can be be measured rather than brightness? (There are plenty of objects brighter than mag 20 which are well beyond the limits of Gaia parallax measurement . ) Without increasing the parallax precision by for example increasing the baseline A "large aperture Gaia" would not add much new distance information, just some intermediate points from less luminous objects. Robin

This was another good thread

The astronomer from across the pond they had on the BBC radio programme ( "inside science" or "science in action", I forget which) likened it to the energy in a pitched baseball so 0.15kg at say 100km/hr (a rather slow pitch ? I'm no expert on that particular sport) which would work out at ~ 0.15*28^2 / 2 = ~ 60 Joules. That's a lot of energy of you happened to be in its way though. How much energy would it dissipate passing through your body I wonder ? Cheers Robin

I guess plants turning our once CO2 rich atmosphere into solid material presumably added a bit in coal seams, though by reversing the process we must be currently causing some net shrinkage. The process is perhaps detectable locally around my observatory where after a decade or so there is no longer a gap between the bottom of the doors and the lawn. Long term everything once on the surface ends up underground due to plate tectonics. Robin

Hi Andy The major disadvantage of this method for wavelength calibration is that the calibration may (and often does with many spectrographs) shift significantly due to thermal and mechanical distortion so it is important to be able to calibrate with the telescope under the actual observing conditions. With the LHIRES for example to reach the kind of precision needed to make these kinds of measurements where 1/5 of a pixel shift is significant https://britastro.org/observations/observation.php?id=20220907_220530_9acdefe378f91ae9 I took calibration lamp spectra before and after every observation ie every 10 minutes. (One of the tests I do on any new spectrograph is to check its stability by taking repeated lamp spectra while the spectrograph cools and then with the telescope pointing in different directions) Cheers Robin

Definitely easier than Andrew's 🙂

While periodically searching my name in NASA ADS looking for any new references to observations I have made (The geek equivalent of Googling oneself!) I came across this curious paper (which cites a paper I was made a co-author of having contributed a single spectrum) https://ui.adsabs.harvard.edu/abs/2022arXiv221100013S/abstract It proposes that the production of a particular class of supernova (Calcium rich type 1a) which are otherwise difficult to explain as the white dwarf producing them appears to be well below the critical mass, might be explained by interaction with (theoretical and as yet unobserved) asteroid mass primordial dark matter black holes. Cheers Robin

also ARASBeAM which links to BeSS and updates with what stars need observing http://arasbeam.free.fr/spip.php?page=beam_belist2&lang=en Valerie Desnoux also publishes a regular report on the spectroscopy forums on Be star activity eg https://groups.io/g/spectro-l/topic/bess_monthly_report_september/101976358 and professional Jon Labadie Bartz has had program with amateur involvement running for several years now comparing spectroscopy and TESS brightness variability https://groups.io/g/spectro-l/topic/classical_be_targets/101618659 Cheers Robin

The Be star candidate search page is still there on the ARAS website http://www.astrosurf.com/aras/be_candidate/auto-be-candidate.html The ARAS forum has been down for some time after a hacking incident trashed it. They have a backup and should eventually be up and running again but it is taking a lot of effort to sort out the associated images I believe Cheers Robin

🙂

Ah ok I was just going on what was in the paper Cheers Robin

I don't think they are challenging the basic concept that planetary nebulae form from the outer layers ejected from red giants leaving a white dwarf, (A process which would still occur even in the absence of a binary companion) Just that the particular morphology and fine detailed structure (in this case and perhaps others) can be understood by considering the presence of binary companions.

Yes that is what I understood but was then surprised to find that physics does not preclude the formation of supermassive dark matter stars, in the early universe at least https://www.scientificamerican.com/article/jwst-might-have-spotted-the-first-dark-matter-stars/

The details need some scientific knowledge but I would say the key observations underpinning the basic "big bang" idea that the universe was once small and hot can (and should) be explainable to non scientists otherwise the layman has a right to be sceptical. Objects in the universe that are further away are measurably moving away from us faster so the universe is expanding and therefore was more compact in the past. https://www.astro.ucla.edu/~wright/cosmo_01.htm Stuff cools as it expands (try setting off a CO2 fire extinguisher) . Except for a few hot spots (stars), the universe is now measurably still a few degrees above zero and so was hotter in the past https://www.astro.ucla.edu/~wright/CMB.html Most of the stuff we see in the universe is made up of only the lightest simplest elements (mostly Hydrogen and a bit of Helium) This because the early universe expanded and cooled rapidly such that the soup of stuff that made up those atoms quickly got too cool and spread out before the larger atoms of the heavier elements could form. The rest of the elements formed in the hot spots (stars) https://www.astro.ucla.edu/~wright/BBNS.html

https://www.astro.ucla.edu/~wright/cosmology_faq.html

An unusual object. Discovered in NGC4388 2023-04-17 and slowly brightened to mag 18 It has now suddenly brightened to mag 13.3 and has been classified as an unusual type 1b-pec based on a spectrum, though the spectrum has not been published on TNS. https://www.wis-tns.org/object/2023fyq Koichi Itagaki image showing the brightened state http://www.k-itagaki.jp/images/AT2023fyq.jpg (Low in the early evening for uk observers) Robin

NED has spectra for galaxies but generally just taken at specific locations. https://ned.ipac.caltech.edu/ For velocity curves, I suspect you will need to dig deeper into the literature though. I think most of these are done at radio wavelengths where the Hydrogen line can be detected out to larger distances Cheers Robin

Not long ago, a large professional team posted the discovery of a bright transient on TNS which when I checked matched the coordinates of Neptune 😉 https://britastro.org/forums/topic/an-independent-discovery-of-neptune Cheers Robin

It exists in the image posted with the discovery (see the fits file from TNS). I don't know why it was withdrawn but there are several possibilities eg not seen in a follow up image, identified as asteroid, hot pixel etc etc

It was withdrawn on TNS on Saturday within a few hours of its "discovery". It is labelled as "unconfirmed" in David Bishop's "rochester" page meaning that someone has looked there and not found anything