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Thanks Andy,
I was thinking it might be interesting to use the personal page like a blog, text images and graphics covering particular topics. (Similar to the BAA articles but in the personal pages.) A combination of the quick post and the image submission functions which don’t quite fill this need individually. Opening up the quick post function to include graphics would do this I think. Is this something that might be considered for the future?
Cheers
Robin
I notice there is no direct access to member pages from the website when not logged in but they are accessible if the link is known eg
https://britastro.org/profile?id=146
https://britastro.org/node/20453
Is this intentional or just the way it works ?
Robin
Finally a clear night last night so was able to take a low noise spectrum at R~500 using the ALPY 600. Using SNID gives an exquisitely good detailed match to several Ia supernovae still a few days from maximum (black is my spectrum red is best match from SNID
Cheers
Robin
A low resolution spectrum from last night. Mainly scattered sunlight but once divided by a nearby G2v solar analogue star spectrum the emission features can be identified. CN at 390nm in the UV is particularly strong.
The raw spectrum image can be seen here
https://britastro.org/node/20453
Cheers
Robin
Currently mag 12.8 as measured by Itagaki compared with his 14.9 discovery magnitude
Yep that was my starting point of course but they are outside the spectrograph guider field.
Cheers
Robin
I don’t do anything currently. I visually examine each exposure and cannot recall seeing anything that I could put down to a satellite. The satellite will not spend long in the slit though so the contribution could be too small to be obvious, just contributing to the uncertainty. They would be more likely to appear in the wider sky background subtraction zones so hopefully the median averaging across the zone deals with them there.
The potential effect on spectroscopy is an interesting one as unlike photometry where trails will be obvious in the image, the cumulative contamination from the trails briefly crossing the slit during say a 20 min exposure, either within the binned or background subtracted regions may not be so obvious.
I did some years ago with a simple setup
http://www.threehillsobservatory.co.uk/astro/spectra_20.htm
but these days in the BAA at least Bill Ward would be the guy to talk to eg
It does indeed seem the fading of Betelgeuse has indeed been greatly exaggerated
I see there is now a recent H,J point in the AAVSO database (The first for over a year)
It shows that Betelgeuse is not fading in the IR where most of the flux is so it does suggest there has not been any significant drop in bolometric luminosity, just a small drop in temperature which has produced an exaggerated effect at V mag, a region sensitive to changes in the depth of the molecular absorption bands.
Cheers
Robin
The latest Atel from the team who originally announced the dimming has some figures on photosphere temperature changes based on IR Wing band filters. They seem to tally reasonably with our estimates from the spectrum change
Hi Andy,
Good point. The V (and R) band does seem to sit in a region which is particularly sensitive to the degree of molecular band absorption which in turn is sensitive to temperature. That additional absorbed flux has to end up elsewhere in the spectrum, most likely in the IR so changes in V mag probably do overestimate the change in total flux as you say.
Here for example is a comparison of standard spectra for M2iii (blue Teff 3600K) compared with M6iii (pink Teff 3100K)
No the individual lines cannot be resolved (Even if the spectrometer had enough resolution they would be broadened in the stellar spectrum to the point where they merged). The depth of the merged bands however gives a measure of the spectral class and therefore Teff even in low resolution spectra. The referenced Atel for example just used photometry in a particular targeted 705nm waveband to estimate the temperature change.
“Measures of Wing TiO-band (705 nm) and near-IR colors indicate that currently Betelgeuse has relatively strong TiO-bands and has a corresponding lower photospheric temperature of T~3580 K (relative to T~ 3660 K near maximum brightness”
Wein’s law is not too much help here as we are seeing just the tail of the black body distribution and stars like these are not really black bodies in any case due to the contribution of the deep absorption lines which varies with temperature
Looking at the Pickles standard spectra (see attached) The change in Betelgeuse looks to correspond to a change in spectral class of around 1-1.5 points eg M2 to M3.5 That is equivalent to a drop in Teff of around 200-300K
The implication is that the contraction in this case could be the result of a reduction in energy production rather than the normal radial pulsation cycle. I am not convinced yet that we are in that situation though rather than the coincidence of the combined effect of the normal pulsations with different periods. If it keeps dropping though….
The short answer is I don’t know. Perhaps the star’s photosphere has reduced in radius by ~30% (and hence halved in surface area) at approximately constant effective temperature ? The original Atel
http://www.astronomerstelegram.org/?read=13341
notes a small drop in Teff, indicated by an increase in the TiO band depths, which I am also seeing but the temperature drop quoted there does not seem to be sufficient on its own to explain the drop in luminosity. Since luminosity goes as T^4, the temperature would need to drop by ~%16 to halve the luminosity.
Interestingly the changes in the spectrum are rather subtle considering the luminosity has roughly halved. Here is a current low resolution spectrum compared with one from the MILES library taken 2000/2001 when the V mag brightness was typically ~0.5
Apparently there’s a lot of money to be made from reducing latency
A point source that bright would be a problem for an amateur setup too but perhaps not if you defocus
http://www.threehillsobservatory.co.uk/astro/SA200_SEPSA_Vega.png
